Introduce a --warn command line option

Replace the singleton --warn-undefined-variables with infrastructure
to manage multiple warnings: the --warn option can take an action
"ignore", "warn", or "error" (which will apply to all warnings), or
a specific warning type and an action for that type.  Multiple
options can be provided and are consolidated.

* NEWS: Announce the new option.
* doc/make.1: Document in the man page.
* doc/make.texi (Warnings): Document in the user's manual.
* Makefile.am: Add new header warning.h.
* src/warning.h: Define enum for actions and warning types, and
macros to test whether they are set.  Keep the default settings
separate so that we can correctly reconstruct MAKEFLAGS.
* src/makeint.h: Remove deprecated warn_undefined_variables_flag.
* src/main.c: Create global variables to hold warning settings.
(switches): Add a new switch for --warn.
(initialize_warnings): Set the default warning actions.
(main): Call initialize_warnings().
(encode_warning_state, decode_warning_state): Convert warning states
between strings and enums.
(encode_warning_name, decode_warning_name): Convert warning names
between strings and enums.
(decode_warn_flags): Convert a --warn option into enum values.  If
deprecated warn_undefined_variables_flag is set convert it to --warn.
(decode_switches): Don't remove duplicates of --warn since order
matters.  Call decode_warn_flags() to handle --warn.
(define_makeflags): Special-case handling of --warn options written
to MAKEFLAGS: write out the current settings.
* src/read.c (tilde_expand): Use new warning control macros.
* src/variable.c (warn_undefined): Ditto.
* src/job.c (construct_command_argv): Ditto.
* tests/scripts/options/warn: Rename from warn-undefined-variables
and add tests for --warn.
* tests/scripts/variables/MAKEFLAGS: Expect the new behavior.

1 files changed, 29 insertions, 1 deletions

diff --git a/doc/make.1 b/doc/make.1
index f02afbee..933a8273 100644
--- a/doc/make.1
+++ b/doc/make.1
@@ -364,8 +364,36 @@ command on the given file before running
 except that the modification time is changed only in the imagination of
 .BR make .
 .TP 0.5i
+\fB\-\-warn\fR[=\fIARG[\fR,\fIARG\fR]]
+Control warning reporting for makefiles.  This option can appear multiple times.
+In case of conflicts, later settings override earlier settings.
+.I ARG
+can be an action; one of
+.IR ignore ,
+.IR warn ,
+or
+.I error
+to set the default action for all warnings, or it can be a specific warning:
+.I undefined-var
+(referencing an undefined variable).  The behavior of each warning can be set
+by adding
+.BI : action
+after the warning name.  If an action is not specified the default is
+.IR warn .
+If no
+.I ARG
+is provided the action for all warnings is
+.IR warn .
+If no
+.B \-\-warn
+option is provided the default action for
+.I undefined-var
+is
+.IR ignore .
+.TP 0.5i
 .B \-\-warn\-undefined\-variables
-Warn when an undefined variable is referenced.
+A deprecated alternative for
+.BR \-\-warn=undefined-var .
 .SH "EXIT STATUS"
 GNU Make exits with a status of zero if all makefiles were successfully parsed
 and no targets that were built failed.  A status of one will be returned