GNU Flymake

This manual is for GNU Flymake (version 0.3, April 2004), which is a universal on-the-fly syntax checker for GNU Emacs.

Copyright © 2004–2018 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License”.

(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

Using Flymake
Extending Flymake
The legacy Proc backend
GNU Free Documentation License
Index

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1 Using Flymake

Flymake is a universal on-the-fly buffer checker implemented as an Emacs minor mode. To use Flymake, you must first activate flymake-mode by using the command flymake-mode.

When enabled, Flymake collects information about problems in the buffer, called diagnostics, from one or more different sources, or backends, and then visually annotates the buffer by highlighting problematic buffer regions with a special face.

It also displays an overall buffer status in the mode line containing totals for different types of diagnostics.

Syntax check is done “on-the-fly”. It is started whenever

Syntax check can also be started manually by typing the M-x flymake-start <RET> command.

flymake-goto-next-error and flymake-goto-prev-error are commands that allow easy navigation to the next/previous erroneous line, respectively. If might be a good idea to map them to M-n and M-p in flymake-mode, by adding to your init file:

     (define-key flymake-mode-map (kbd "M-n") 'flymake-goto-next-error)
     (define-key flymake-mode-map (kbd "M-p") 'flymake-goto-prev-error)

Flymake is a universal syntax checker in the sense that it's easily extended to support new backends (see Extending Flymake).

Historically, Flymake used to accept diagnostics from a single backend, albeit a reasonably flexible one.

This backend isn't (yet) obsolete, and so is still available as a fallback and active by default (see The legacy Proc backend). It works by selecting a syntax check tool from a preconfigured list (compiler for C++ files, perl for Perl files, etc.), and executing it in the background, passing it a temporary file which is a copy of the current buffer, and parsing the output for known error/warning message patterns.

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1.1 Syntax check statuses

When enabled, Flymake displays its status in the mode line, which provides a visual summary of diagnostic collection. It may also hint at certain exceptional situations encountered when communicating with backends.

The following statuses are defined:

[nerrors nwarnings ...] Normal operation. nerrors and nwarnings are, respectively, the total number of errors and warnings found during the last buffer check, for all backends. They may be followed by other totals for other types of diagnostics (see Flymake error types).


Wait Some Flymake backends haven't reported since the last time they where questioned. It is reasonable to assume that this is a temporary delay and Flymake will resume normal operation soon.


! All the configured Flymake backends have disabled themselves: Flymake cannot annotate the buffer and action from the user is needed to investigate and remedy the situation (see Backend exceptions).


? There are no applicable Flymake backends for this buffer, thus Flymake cannot annotate it. To fix this, a user may look to extending Flymake and add a new backend (see Extending Flymake).

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1.2 Backend exceptions

Some backends may take longer than others to respond or complete, and some may decide to disable themselves if they are not suitable for the current buffer or encounter some unavoidable problem. A disabled backend is not tried again for future checks of the current buffer.

The commands flymake-reporting-backends, flymake-running-backends and flymake-disabled-backends show the backends currently used and those which are disabled.

Toggling flymake-mode off and on again, or invoking flymake-start with a prefix argument is one way to reset the disabled backend list, so that they will be tried again in the next check.

Flymake also uses a simple logging facility for indicating important points in the control flow. The logging facility sends logging messages to the *Flymake log* buffer. The information logged can be used for resolving various problems related to Flymake. For convenience, a shortcut to this buffer can be found in Flymake's menu, accessible from the top menu bar or just left of the status indicator.

Logging output is controlled by the Emacs warning-minimum-log-level and warning-minimum-level variables.

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1.3 Customizable variables

This section summarizes customization variables used for the configuration of the Flymake user interface.

flymake-no-changes-timeout
If any changes are made to the buffer, syntax check is automatically started after this many seconds, unless the user makes another change, which resets the timer.
flymake-start-syntax-check-on-newline
A boolean flag indicating whether to start syntax check immediately after a newline character is inserted into the buffer.
flymake-start-on-flymake-mode
A boolean flag indicating whether to start syntax check immediately after enabling flymake-mode.
flymake-error
A custom face for highlighting regions for which an error has been reported.
flymake-warning
A custom face for highlighting regions for which a warning has been reported.
flymake-note
A custom face for highlighting regions for which a note has been reported.
flymake-error-bitmap
A bitmap used in the fringe to mark lines for which an error has been reported.
flymake-warning-bitmap
A bitmap used in the fringe to mark lines for which a warning has been reported.
flymake-fringe-indicator-position
Which fringe (if any) should show the warning/error bitmaps.
flymake-wrap-around
If non-nil, moving to errors with flymake-goto-next-error and flymake-goto-prev-error wraps around buffer boundaries.

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2 Extending Flymake

Flymake can primarily be extended in one of two ways:

  1. By changing the look and feel of the annotations produced by the different backends.
  2. By adding a new buffer-checking backend.

The following sections discuss each approach in detail.

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2.1 Customizing Flymake error types

The variable flymake-diagnostic-types-alist is looked up by Flymake every time an annotation for a diagnostic is created in the buffer. Specifically, this variable holds a table of correspondence between symbols designating diagnostic types and an additional sub-table of properties pertaining to each diagnostic type.

Both tables are laid out in association list (see Association Lists) format, and thus can be conveniently accessed with the functions of the assoc family.

You can use any symbol-value association in the properties sub-table, but some symbols have special meaning as to where and how Flymake presents the diagnostic:

Three default diagnostic types, :error, :warning and :note are predefined in flymake-diagnostic-types-alist. By default each lists a single flymake-category property whose value is, respectively, the symbols flymake-error, flymake-warning and flymake-note.

These category symbols' plists is where the values of customizable variables and faces such as flymake-error-bitmap are found. Thus, if you change their plists, Flymake may stop honoring these user customizations.

The flymake-category special property is also especially useful for backends which create diagnostics objects with non-default types that differ from an existing type by only a few properties (see Flymake utility functions).

As an example, consider configuring a new diagnostic type :low-priority-note that behaves much like the :note priority but without an overlay face.

     (add-to-list
      'flymake-diagnostic-types-alist
      `(:low-priority-note . ((face . nil)
                              (flymake-category . flymake-note))))

As you might have guessed, Flymake's annotations are implemented as overlays (see Overlays). Along with the properties that you specify for the specific type of diagnostic, Flymake adds the property flymake-diagnostic to these overlays, and sets it to the object that the backend created with flymake-make-diagnostic.

Since overlays also support arbitrary keymaps, you can use this along with the functions flymake-diagnostics and flymake-diagnostic-text (see Flymake utility functions) to create interactive annotations, such as in the following example of binding a mouse-3 event (middle mouse button click) to an Internet search for the text of a :warning or :error.

     (defun my-search-for-message (event)
       (interactive "e")
       (let* ((diags (flymake-diagnostics (posn-point (event-start event))))
              (topmost-diag (car diags)))
         (eww-browse-url
            (concat
             "https://duckduckgo.com/?q="
             (replace-regexp-in-string " "
                                       "+"
                                       (flymake-diagnostic-text topmost-diag)))
            t)))
     
     (dolist (type '(:warning :error))
       (let ((a (assoc type flymake-diagnostic-types-alist)))
         (setf (cdr a)
               (append `((mouse-face . highlight)
                         (keymap . ,(let ((map (make-sparse-keymap)))
                                      (define-key map [mouse-2]
                                        'my-search-for-message)
                                      map)))
                       (cdr a)))))

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2.2 Backend functions

Flymake backends are Lisp functions placed in the special hook flymake-diagnostic-functions.

A backend's responsibility is to diagnose the contents of a buffer for problems, registering the problem's positions, type, and summary description. This information is collected in the form of diagnostic objects created by the function flymake-make-diagnostic (see Flymake utility functions), and then handed over to Flymake, which proceeds to annotate the buffer.

A request for a buffer check, and the subsequent delivery of diagnostics, are two key events of the interaction between Flymake and backend. Each such event corresponds to a well-defined function calling convention: one for calls made by Flymake into the backend via the backend function, the other in the reverse direction via a callback. To be usable, backends must adhere to both.

Backend functions must accept an arbitrary number of arguments:

Whenever Flymake or the user decide to re-check the buffer, backend functions are called as detailed above, and are expected to initiate this check, but aren't in any way required to complete it before exiting: if the computation involved is expensive, as is often the case with large buffers, that slower task should be scheduled for the future using asynchronous sub-processes (see Asynchronous Processes) or other asynchronous mechanisms.

In any case, backend functions are expected to return quickly or signal an error, in which case the backend is disabled (see Backend exceptions).

If the function returns, Flymake considers the backend to be running. If it has not done so already, the backend is expected to call the function report-fn passed to it, at which point Flymake considers the backend to be reporting. Backends call report-fn by passing it a single argument report-action followed by an optional list of keyword-value pairs of the form (:report-key value :report-key2 value2...).

Currently accepted values for report-action are:

Currently accepted report-key arguments are:

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2.2.1 Flymake utility functions

Before delivering them to Flymake, backends create diagnostic objects by calling the function flymake-make-diagnostic.

— Function: flymake-make-diagnostic buffer beg end type text

Make a Flymake diagnostic for buffer's region from beg to end. type is a key to flymake-diagnostic-types-alist and text is a description of the problem detected in this region.

These objects' properties can be accessed with the functions flymake-diagnostic-backend, flymake-diagnostic-buffer, flymake-diagnostic-text, flymake-diagnostic-beg, flymake-diagnostic-end and flymake-diagnostic-type.

Additionally, the function flymake-diagnostics will collect such objects in the region you specify.

— Function: flymake-diagnostics beg end

Get a list of Flymake diagnostics in the region determined by beg and end. If neither beg or end is supplied, use the whole buffer, otherwise if beg is non-nil and end is nil, consider only diagnostics at beg.

It is often the case with external syntax tools that a diagnostic's position is reported in terms of a line number, and sometimes a column number. To convert this information into a buffer position, backends can use the following function:

— Function: flymake-diag-region buffer line &optional col

Compute buffer's region (beg . end) corresponding to line and col. If col is nil, return a region just for line. Return nil if the region is invalid.

For troubleshooting purposes, backends may record arbitrary exceptional or erroneous situations into the Flymake log buffer (see Backend exceptions):

— Macro: flymake-log level msg &optional args

Log, at level level, the message msg formatted with args. level is passed to display-warning (see Warning Basics), which is used to display the warning in Flymake's log buffer.

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2.2.2 An annotated example backend

This section presents an annotated example of a complete working Flymake backend. The example illustrates the process of writing a backend as outlined above.

The backend in question is used for checking Ruby source files. It uses asynchronous sub-processes (see Asynchronous Processes), a common technique for performing parallel processing in Emacs.

The following code needs lexical binding (see Using Lexical Binding) to be active.

     ;;; ruby-flymake.el --- A ruby Flymake backend  -*- lexical-binding: t; -*-
     (defvar-local ruby--flymake-proc nil)
     
     (defun ruby-flymake (report-fn &rest _args)
       ;; Not having a ruby interpreter is a serious problem which should cause
       ;; the backend to disable itself, so an error is signaled.
       ;;
       (unless (executable-find
                "ruby") (error "Cannot find a suitable ruby"))
       ;; If a live process launched in an earlier check was found, that
       ;; process is killed.  When that process's sentinel eventually runs,
       ;; it will notice its obsoletion, since it have since reset
       ;; `ruby-flymake-proc' to a different value
       ;;
       (when (process-live-p ruby--flymake-proc)
         (kill-process ruby--flymake-proc))
     
       ;; Save the current buffer, the narrowing restriction, remove any
       ;; narrowing restriction.
       ;;
       (let ((source (current-buffer)))
         (save-restriction
           (widen)
           ;; Reset the `ruby--flymake-proc' process to a new process
           ;; calling the ruby tool.
           ;;
           (setq
            ruby--flymake-proc
            (make-process
             :name "ruby-flymake" :noquery t :connection-type 'pipe
             ;; Make output go to a temporary buffer.
             ;;
             :buffer (generate-new-buffer " *ruby-flymake*")
             :command '("ruby" "-w" "-c")
             :sentinel
             (lambda (proc _event)
               ;; Check that the process has indeed exited, as it might
               ;; be simply suspended.
               ;;
               (when (eq 'exit (process-status proc))
                 (unwind-protect
                     ;; Only proceed if `proc' is the same as
                     ;; `ruby--flymake-proc', which indicates that
                     ;; `proc' is not an obsolete process.
                     ;;
                     (if (with-current-buffer source (eq proc ruby--flymake-proc))
                         (with-current-buffer (process-buffer proc)
                           (goto-char (point-min))
                           ;; Parse the output buffer for diagnostic's
                           ;; messages and locations, collect them in a list
                           ;; of objects, and call `report-fn'.
                           ;;
                           (cl-loop
                            while (search-forward-regexp
                                   "^\\(?:.*.rb\\|-\\):\\([0-9]+\\): \\(.*\\)$"
                                   nil t)
                            for msg = (match-string 2)
                            for (beg . end) = (flymake-diag-region
                                               source
                                               (string-to-number (match-string 1)))
                            for type = (if (string-match "^warning" msg)
                                           :warning
                                         :error)
                            collect (flymake-make-diagnostic source
                                                             beg
                                                             end
                                                             type
                                                             msg)
                            into diags
                            finally (funcall report-fn diags)))
                       (flymake-log :warning "Canceling obsolete check %s"
                                    proc))
                   ;; Cleanup the temporary buffer used to hold the
                   ;; check's output.
                   ;;
                   (kill-buffer (process-buffer proc)))))))
           ;; Send the buffer contents to the process's stdin, followed by
           ;; an EOF.
           ;;
           (process-send-region ruby--flymake-proc (point-min) (point-max))
           (process-send-eof ruby--flymake-proc))))
     
     (defun ruby-setup-flymake-backend ()
       (add-hook 'flymake-diagnostic-functions 'ruby-flymake nil t))
     
     (add-hook 'ruby-mode-hook 'ruby-setup-flymake-backend)

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3 The legacy “Proc” backend

The backend flymake-proc-legacy-backend was originally designed to be extended for supporting new syntax check tools and error message patterns. It is also controlled by its own set of customization variables

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3.1 Customization variables for the Proc backend

flymake-proc-allowed-file-name-masks
A list of (filename-regexp, init-function, cleanup-function getfname-function) for configuring syntax check tools. See Adding support for a new syntax check tool.
flymake-proc-master-file-dirs
A list of directories for searching a master file. See Locating a master file.
flymake-proc-get-project-include-dirs-function
A function used for obtaining a list of project include dirs (C/C++ specific). See Getting the include directories.
flymake-proc-master-file-count-limit
flymake-proc-check-file-limit
Used when looking for a master file. See Locating a master file.
flymake-proc-err-line-patterns
Patterns for error/warning messages in the form (regexp file-idx line-idx col-idx err-text-idx). See Parsing the output.
flymake-proc-diagnostic-type-pred
A function to classify a diagnostic text as particular type of error. Should be a function taking an error text and returning one of the symbols indexing flymake-diagnostic-types-alist. If non-nil is returned but there is no such symbol in that table, a warning is assumed. If nil is returned, an error is assumed. Can also be a regular expression that should match only warnings. This variable replaces the old flymake-warning-re and flymake-warning-predicate.
flymake-proc-compilation-prevents-syntax-check
A flag indicating whether compilation and syntax check of the same file cannot be run simultaneously. See Interaction with other modes.

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3.2 Adding support for a new syntax check tool

Syntax check tools are configured using the flymake-proc-allowed-file-name-masks list. Each item of this list has the following format:

     (filename-regexp, init-function, cleanup-function, getfname-function)
filename-regexp
This field is used as a key for locating init/cleanup/getfname functions for the buffer. Items in flymake-proc-allowed-file-name-masks are searched sequentially. The first item with filename-regexp matching buffer filename is selected. If no match is found, flymake-mode is switched off.
init-function
init-function is required to initialize the syntax check, usually by creating a temporary copy of the buffer contents. The function must return (list cmd-name arg-list). If init-function returns null, syntax check is aborted, but flymake-mode is not switched off.
cleanup-function
cleanup-function is called after the syntax check process is complete and should take care of proper deinitialization, which is usually deleting a temporary copy created by the init-function.
getfname-function
This function is used for translating filenames reported by the syntax check tool into “real” filenames. Filenames reported by the tool will be different from the real ones, as actually the tool works with the temporary copy. In most cases, the default implementation provided by Flymake, flymake-proc-get-real-file-name, can be used as getfname-function.

To add support for a new syntax check tool, write the corresponding init-function and, optionally, cleanup-function and getfname-function. If the format of error messages reported by the new tool is not yet supported by Flymake, add a new entry to the flymake-proc-err-line-patterns list.

The following sections contain some examples of configuring Flymake support for various syntax check tools.

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3.2.1 Example—Configuring a tool called directly

In this example, we will add support for perl as a syntax check tool. perl supports the -c option which does syntax checking.

First, we write the init-function:

     (defun flymake-proc-perl-init ()
       (let* ((temp-file (flymake-proc-init-create-temp-buffer-copy
                          'flymake-proc-create-temp-inplace))
              (local-file (file-relative-name
                           temp-file
                           (file-name-directory buffer-file-name))))
         (list "perl" (list "-wc " local-file))))

flymake-proc-perl-init creates a temporary copy of the buffer contents with the help of flymake-proc-init-create-temp-buffer-copy, and builds an appropriate command line.

Next, we add a new entry to the flymake-proc-allowed-file-name-masks:

     (setq flymake-proc-allowed-file-name-masks
           (cons '(".+\\.pl$"
                   flymake-proc-perl-init
                   flymake-proc-simple-cleanup
                   flymake-proc-get-real-file-name)
                 flymake-proc-allowed-file-name-masks))

Note that we use standard cleanup-function and getfname-function.

Finally, we add an entry to flymake-proc-err-line-patterns:

     (setq flymake-proc-err-line-patterns
           (cons '("\\(.*\\) at \\([^ \n]+\\) line \\([0-9]+\\)[,.\n]"
                   2 3 nil 1)
                 flymake-proc-err-line-patterns))

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3.2.2 Example—Configuring a tool called via make

In this example we will add support for C files syntax checked by gcc called via make.

We're not required to write any new functions, as Flymake already has functions for make. We just add a new entry to the flymake-proc-allowed-file-name-masks:

     (setq flymake-proc-allowed-file-name-masks
           (cons '(".+\\.c$"
                   flymake-proc-simple-make-init
                   flymake-proc-simple-cleanup
                   flymake-proc-get-real-file-name)
                 flymake-proc-allowed-file-name-masks))

flymake-proc-simple-make-init builds the following make command line:

     (list "make"
           (list "-s" "-C"
                 base-dir
                 (concat "CHK_SOURCES=" source)
                 "SYNTAX_CHECK_MODE=1"
                 "check-syntax"))

base-dir is a directory containing the Makefile, see Locating the buildfile.

Thus, Makefile must contain the check-syntax target. In our case this target might look like this:

check-syntax:
	gcc -o /dev/null -S ${CHK_SOURCES} || true

The format of error messages reported by gcc is already supported by Flymake, so we don't have to add a new entry to flymake-err-line-patterns. Note that if you are using Automake, you may want to replace gcc with the standard Automake variable COMPILE:

check-syntax:
	$(COMPILE) -o /dev/null -S ${CHK_SOURCES} || true

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3.3 Implementation overview

flymake-proc-legacy-backend saves a copy of the buffer in a temporary file in the buffer's directory (or in the system temporary directory, for Java files), creates a syntax check command and launches a process with this command. The output is parsed using a list of error message patterns, and error information (file name, line number, type and text) is saved. After the process has finished, Flymake highlights erroneous lines in the buffer using the accumulated error information.

Syntax check is considered possible if there's an entry in flymake-proc-allowed-file-name-masks matching buffer's filename and its init-function returns non-nil value.

Two syntax check modes are distinguished:

  1. Buffer can be syntax checked in a standalone fashion, that is, the file (its temporary copy, in fact) can be passed over to the compiler to do the syntax check. Examples are C/C++ sources (.c, .cpp) and Java (.java).
  2. Buffer can be syntax checked, but additional file, called master file, is required to perform this operation. A master file is a file that includes the current file, so that running a syntax check tool on it will also check syntax in the current file. Examples are C/C++ headers (.h, .hpp).

These modes are handled inside init/cleanup/getfname functions, see Adding support for a new syntax check tool.

The Proc backend contains implementations of all functionality required to support different syntax check modes described above (making temporary copies, finding master files, etc.), as well as some tool-specific (routines for Make, Ant, etc.) code.

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3.4 Making a temporary copy

After the possibility of the syntax check has been determined, a temporary copy of the current buffer is made so that the most recent unsaved changes could be seen by the syntax check tool. Making a copy is quite straightforward in a standalone case (mode 1), as it's just saving buffer contents to a temporary file.

Things get trickier, however, when master file is involved, as it requires to

Locating a master file is discussed in the following section.

Patching just changes all appropriate lines of the master file so that they use the new (temporary) name of the current file. For example, suppose current file name is file.h, the master file is file.cpp, and it includes current file via #include "file.h". Current file's copy is saved to file file_flymake.h, so the include line must be changed to #include "file_flymake.h". Finally, patched master file is saved to file_flymake_master.cpp, and the last one is passed to the syntax check tool.

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3.5 Locating a master file

Master file is located in two steps.

First, a list of possible master files is built. A simple name matching is used to find the files. For a C++ header file.h, the Proc backend searches for all .cpp files in the directories whose relative paths are stored in a customizable variable flymake-proc-master-file-dirs, which usually contains something like ("." "./src"). No more than flymake-proc-master-file-count-limit entries is added to the master file list. The list is then sorted to move files with names file.cpp to the top.

Next, each master file in a list is checked to contain the appropriate include directives. No more than flymake-proc-check-file-limit of each file are parsed.

For file.h, the include directives to look for are #include "file.h", #include "../file.h", etc. Each include is checked against a list of include directories (see Getting the include directories) to be sure it points to the correct file.h.

First matching master file found stops the search. The master file is then patched and saved to disk. In case no master file is found, syntax check is aborted, and corresponding status (‘!’) is reported in the mode line. See Syntax check statuses.

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3.6 Getting the include directories

Two sets of include directories are distinguished: system include directories and project include directories. The former is just the contents of the INCLUDE environment variable. The latter is not so easy to obtain, and the way it can be obtained can vary greatly for different projects. Therefore, a customizable variable flymake-proc-get-project-include-dirs-function is used to provide the way to implement the desired behavior.

The default implementation, flymake-proc-get-project-include-dirs-imp, uses a make call. This requires a correct base directory, that is, a directory containing a correct Makefile, to be determined.

As obtaining the project include directories might be a costly operation, its return value is cached in the hash table. The cache is cleared in the beginning of every syntax check attempt.

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3.7 Locating the buildfile

The Proc backend can be configured to use different tools for performing syntax checks. For example, it can use direct compiler call to syntax check a perl script or a call to make for a more complicated case of a C/C++ source. The general idea is that simple files, like Perl scripts and HTML pages, can be checked by directly invoking a corresponding tool. Files that are usually more complex and generally used as part of larger projects, might require non-trivial options to be passed to the syntax check tool, like include directories for C++. The latter files are syntax checked using some build tool, like Make or Ant.

All Make configuration data is usually stored in a file called Makefile. To allow for future extensions, Flymake uses a notion of buildfile to reference the project configuration file.

Special function, flymake-proc-find-buildfile is provided for locating buildfiles. Searching for a buildfile is done in a manner similar to that of searching for possible master files. In case there's no build file, the syntax check is aborted.

Buildfile values are also cached.

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3.8 Starting the syntax check process

The command line (command name and the list of arguments) for launching a process is returned by the initialization function. The Proc backend then just starts an asynchronous process and configures a process filter and sentinel, which are used for processing the output of the syntax check tool. When exiting Emacs, running processes will be killed without prompting the user.

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3.9 Parsing the output

The output generated by the syntax check tool is parsed in the process filter/sentinel using the error message patterns stored in the flymake-proc-err-line-patterns variable. This variable contains a list of items of the form (regexp file-idx line-idx err-text-idx), used to determine whether a particular line is an error message and extract file name, line number and error text, respectively. Error type (error/warning) is also guessed by matching error text with the ‘^[wW]arning’ pattern. Anything that was not classified as a warning is considered an error. Type is then used to sort error menu items, which shows error messages first.

The Proc backend is also able to interpret error message patterns missing err-text-idx information. This is done by merely taking the rest of the matched line ((substring line (match-end 0))) as error text. This trick allows making use of a huge collection of error message line patterns from compile.el. All these error patterns are appended to the end of flymake-proc-err-line-patterns.

The error information obtained is saved in a buffer local variable. The buffer for which the process output belongs is determined from the process-id->buffer mapping updated after every process launch/exit.

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3.10 Interaction with other modes

The only mode the Proc backend currently knows about is compile.

The Proc backend can be configured to not start syntax check if it thinks the compilation is in progress, by testing the compilation-in-progress variable. The reason why this might be useful is saving CPU time in case both syntax check and compilation are very CPU intensive. The original reason for adding this feature, though, was working around a locking problem with MS Visual C++ compiler. The variable in question is flymake-proc-compilation-prevents-syntax-check.

The Proc backend also provides an alternative command for starting compilation, flymake-proc-compile. It just kills all the active syntax check processes before calling compile.

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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     https://fsf.org/
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

    The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

    A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

    Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

    The “publisher” means any person or entity that distributes copies of the Document to the public.

    A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

    The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

  5. MODIFICATIONS

    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
    13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. Preserve any Warranty Disclaimers.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

  6. COMBINING DOCUMENTS

    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

  7. COLLECTIONS OF DOCUMENTS

    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

  8. AGGREGATION WITH INDEPENDENT WORKS

    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

  9. TRANSLATION

    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/licenses/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

  12. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being list their titles, with
         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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Index