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9.3 Reporting Messages

When macros statically diagnose abnormal situations, benign or fatal, they should report them using these macros. For dynamic issues, i.e., when configure is run, see Printing Messages.

— Macro: AC_DIAGNOSE (category, message)

Report message as a warning (or as an error if requested by the user) if warnings of the category are turned on. You are encouraged to use standard categories, which currently include:

messages that don't fall into one of the following categories. Use of an empty category is equivalent.
related to cross compilation issues.
use of an obsolete construct.
dubious syntactic constructs, incorrectly ordered macro calls.

— Macro: AC_WARNING (message)

Equivalent to ‘AC_DIAGNOSE([syntax], message)’, but you are strongly encouraged to use a finer grained category.

— Macro: AC_FATAL (message)

Report a severe error message, and have autoconf die.

When the user runs ‘autoconf -W error’, warnings from AC_DIAGNOSE and AC_WARNING are reported as error, see autoconf Invocation.