Flymake is a universal on-the-fly syntax checker implemented as an
Emacs minor mode. Flymake runs the pre-configured syntax check tool
(compiler for C++ files, perl for perl files, etc.) in the
background, passing it a temporary copy of the current buffer, and
parses the output for known error/warning message patterns. Flymake
then highlights erroneous lines (i.e. lines for which at least one
error or warning has been reported by the syntax check tool), and
displays an overall buffer status in the mode line. Status information
displayed by Flymake contains total number of errors and warnings
reported for the buffer during the last syntax check.
flymake-goto-next-error and flymake-goto-prev-error
functions allow for easy navigation to the next/previous erroneous
line, respectively.
Calling flymake-display-err-menu-for-current-line will popup a
menu containing error messages reported by the syntax check tool for
the current line. Errors/warnings belonging to another file, such as a
.h header file included by a .c file, are shown in the
current buffer as belonging to the first line. Menu items for such
messages also contain a filename and a line number. Selecting such a
menu item will automatically open the file and jump to the line with
error.
Syntax check is done 'on-the-fly'. It is started whenever
0.5 seconds ago (the
delay is configurable).
Flymake is a universal syntax checker in the sense that it's easily extended to support new syntax check tools and error message patterns. See Configuring Flymake.
Flymake is packaged in a single file, flymake.el.
To install/update Flymake, place flymake.el to a directory
somewhere on Emacs load path. You might also want to byte-compile
flymake.el to improve performance.
Also, place the following line in the .emacs file.
(require 'flymake)
You might also map the most frequently used Flymake functions, such as
flymake-goto-next-error, to some keyboard shortcuts:
(global-set-key [f3] 'flymake-display-err-menu-for-current-line)
(global-set-key [f4] 'flymake-goto-next-error)
Flymake is an Emacs minor mode. To use Flymake, you
must first activate flymake-mode by using the
flymake-mode function.
Instead of manually activating flymake-mode, you can configure
Flymake to automatically enable flymake-mode upon opening any
file for which syntax check is possible. To do so, place the following
line in .emacs:
(add-hook 'find-file-hook 'flymake-find-file-hook)
When flymake-mode is active, syntax check is started
automatically on any of the three conditions mentioned above. Syntax
check can also be started manually by using the
flymake-start-syntax-check-for-current-buffer function. This
can be used, for example, when changes were made to some other buffer
affecting the current buffer.
After syntax check is completed, lines for which at least one error or warning has been reported are highlighted, and total number of errors and warning is shown in the mode line. Use the following functions to navigate the highlighted lines.
flymake-goto-next-error
| Moves point to the next erroneous line, if any.
|
flymake-goto-prev-error
| Moves point to the previous erroneous line.
|
These functions treat erroneous lines as a linked list. Therefore,
flymake-goto-next-error will go to the first erroneous line
when invoked in the end of the buffer.
To view error messages belonging to the current line, use the
flymake-display-err-menu-for-current-line function. If there's
at least one error or warning reported for the current line, this
function will display a popup menu with error/warning texts.
Selecting the menu item whose error belongs to another file brings
forward that file with the help of the
flymake-goto-file-and-line function.
After syntax check is finished, its status is displayed in the mode line. The following statuses are defined.
| Flymake* or Flymake:E/W* | Flymake is currently running. For the second case, E/W contains the
error and warning count for the previous run.
|
| Flymake | Syntax check is not running. Usually this means syntax check was
successfully passed (no errors, no warnings). Other possibilities are:
syntax check was killed as a result of executing
flymake-compile, or syntax check cannot start as compilation
is currently in progress.
|
| Flymake:E/W | Number of errors/warnings found by the syntax check process.
|
| Flymake:! | Flymake was unable to find master file for the current buffer.
|
The following errors cause a warning message and switch flymake mode OFF for the buffer.
| CFGERR | Syntax check process returned nonzero exit code, but no
errors/warnings were reported. This indicates a possible configuration
error (for example, no suitable error message patterns for the
syntax check tool).
|
| NOMASTER | Flymake was unable to find master file for the current buffer.
|
| NOMK | Flymake was unable to find a suitable buildfile for the current buffer.
|
| PROCERR | Flymake was unable to launch a syntax check process.
|
Flymake uses a simple logging facility for indicating important points
in the control flow. The logging facility sends logging messages to
the *Messages* buffer. The information logged can be used for
resolving various problems related to Flymake.
Logging output is controlled by the flymake-log-level
variable. 3 is the most verbose level, and -1 switches
logging off.
Flymake was designed to be easily extended for supporting new syntax check tools and error message patterns.
This section summarizes variables used for Flymake configuration.
flymake-log-levelflymake-allowed-file-name-masks(filename-regexp, init-function, cleanup-function
getfname-function) for configuring syntax check tools. See Adding support for a new syntax check tool.
flymake-buildfile-dirsflymake-master-file-dirsflymake-get-project-include-dirs-functionflymake-master-file-count-limitflymake-check-file-limitflymake-err-line-patterns(regexp file-idx
line-idx err-text-idx). See Parsing the output.
flymake-compilation-prevents-syntax-checkflymake-no-changes-timeoutflymake-no-changes-timeout seconds.
flymake-gui-warnings-enabledflymake-gui-warnings-enabled is
nil, these errors will only be logged to the *Messages*
buffer.
flymake-start-syntax-check-on-newlineflymake-errline-faceflymake-warnline-faceSyntax check tools are configured using the
flymake-allowed-file-name-masks list. Each item of this list
has the following format:
(filename-regexp, init-function, cleanup-function, getfname-function)
filename-regexpflymake-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-functioninit-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, by
flymake-mode is not switched off.
cleanup-functioncleanup-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-functionflymake-get-real-file-name, can be used as
getfname-function.
To add support for a new syntax check tool, write 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-err-line-patterns list.
The following sections contain some examples of configuring Flymake support for various syntax check tools.
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-perl-init (buffer)
(let* ((temp-file (flymake-init-create-temp-buffer-copy
buffer 'flymake-create-temp-inplace))
(local-file (concat (flymake-build-relative-filename
(file-name-directory
(buffer-file-name
(current-buffer)))
(file-name-directory temp-file))
(file-name-nondirectory temp-file))))
(list "perl" (list "-wc " local-file))))
flymake-perl-init creates a temporary copy of the buffer
contents with the help of
flymake-init-create-temp-buffer-copy, and builds an appropriate
command line.
Next, we add a new entry to the
flymake-allowed-file-name-masks:
(setq flymake-allowed-file-name-masks
(cons '(".+\\.pl$"
flymake-perl-init
flymake-simple-cleanup
flymake-get-real-file-name)
flymake-allowed-file-name-masks))
Note that we use standard cleanup-function and
getfname-function.
Finally, we add an entry to flymake-err-line-patterns:
(setq flymake-err-line-patterns
(cons '("\\(.*\\) at \\([^ \n]+\\) line \\([0-9]+\\)[,.\n]"
2 3 nil 1)
flymake-err-line-patterns))
In this example we will add support for C files syntax checked by
gcc called via make.
We're not required to write any new functions, as Flymake already has
functions for make. We just add a new entry to the
flymake-allowed-file-name-masks:
(setq flymake-allowed-file-name-masks
(cons '(".+\\.c$"
flymake-simple-make-init
flymake-simple-cleanup
flymake-get-real-file-name)
flymake-allowed-file-name-masks))
flymake-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 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 nul -S ${CHK_SOURCES}
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.
Syntax check is started by calling flymake-start-syntax-check-for-current-buffer.
Flymake first determines whether it is able to do syntax
check. It then saves a copy of the buffer in a temporary file in the
buffer's directory (or in the system temp 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-allowed-file-name-masks matching buffer's filename and
its init-function returns non-nil value.
Two syntax check modes are distinguished:
These modes are handled inside init/cleanup/getfname functions, see Adding support for a new syntax check tool.
Flymake 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.
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.
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,
Flymake searches for all .cpp files in the directories whose relative paths are
stored in a customizable variable flymake-master-file-dirs, which
usually contains something like ("." "./src"). No more than
flymake-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-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.
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-get-project-include-dirs-function is used to provide the
way to implement the desired behavior.
The default implementation, flymake-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.
Flymake 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-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. A customizable variable
flymake-buildfile-dirs holds a list of relative paths to the
buildfile. They are checked sequentially until a buildfile is found. In case
there's no build file, syntax check is aborted.
Buildfile values are also cached.
The command line (command name and the list of arguments) for launching a process is returned by the
initialization function. Flymake then just calls start-process
to start an asynchronous process and configures process filter and
sentinel which is used for processing the output of the syntax check
tool.
The output generated by the syntax check tool is parsed in the process
filter/sentinel using the error message patterns stored in the
flymake-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.
Flymake 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
to make use of a huge collection of error message line patterns from
compile.el. All these error patterns are appended to
the end of flymake-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.
Highlighting is implemented with overlays and happens in the process
sentinel, after calling the cleanup function. Two customizable faces
are used: flymake-errline-face and
flymake-warnline-face. Errors belonging outside the current
buffer are considered to belong to line 1 of the current buffer.
The only mode flymake currently knows about is compile.
Flymake can be configured to not start syntax check if it thinks the
compilation is in progress. The check is made by the
flymake-compilation-is-running, which tests 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.
Flymake also provides an alternative command for starting compilation,
flymake-compile:
(defun flymake-compile ()
"Kill all flymake syntax checks then start compilation."
(interactive)
(flymake-stop-all-syntax-checks)
(call-interactively 'compile))
It just kills all the active syntax check processes before calling
compile.
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