FORCE_C_STD and FORCE_CXX_STD

[nia <nia%NetBSD.org@localhost>]

This patch is designed to replace several common patterns in pkgsrc:

- A package uses a feature from a newer language standard without
  declaring so, effectively assuming the compiler defaults to
  a newer standard. This replaces the pattern:

# "error: 'for' loop initial declarations are only allowed in C99 mode"
USE_LANGUAGES=	c99

with

# "error: 'for' loop initial declarations are only allowed in C99 mode"
FORCE_C_STD=	c99

- A package is old and uses deprecated language features without
  setting std, failing with compilers that default to a newer standard.
  This replaces the pattern:

USE_LANGUAGES=	c c++03

with

USE_LANGUAGES=	c c++

# fails with C++14 default
FORCE_CXX_STD=	c++03

- A package uses standard library features that depend on non-standard
  compiler extensions without realizing.
  This replaces the pattern:

# Also needed for alloca(), c99 creeps in and overrides otherwise...
BUILDLINK_TRANSFORM+=  opt:-std=c99:-std=gnu99

with

# Also needed for alloca(), c99 creeps in and overrides otherwise...
FORCE_C_STD=	gnu99

Index: doc/guide/files/fixes.xml
===================================================================
RCS file: /cvsroot/pkgsrc/doc/guide/files/fixes.xml,v
retrieving revision 1.190
diff -u -p -u -r1.190 fixes.xml
--- doc/guide/files/fixes.xml	26 Jul 2023 22:41:02 -0000	1.190
+++ doc/guide/files/fixes.xml	29 Jul 2023 21:30:07 -0000
@@ -1433,19 +1433,12 @@ MESON_ARGS+=	-Dx11=false
     the <varname>USE_LANGUAGES</varname> variable. Allowed values
     currently are:
 <programlisting>
-c99, c++, c++03, gnu++03, c++0x, gnu++0x, c++11, gnu++11,
-c++14, gnu++14, c++17, gnu++17, c++20, gnu++20, fortran,
-fortran77, java, objc, obj-c++, and ada.
+c, c++, fortran, fortran77, java, objc, obj-c++, and ada.
 </programlisting>
     (and any combination).  The default is
     <quote>c</quote>.  Packages using GNU configure scripts, even if
     written in C++, usually need a C compiler for the configure
     phase.
-    Language variants like <literal>c++11</literal>
-    can be specified if the package does not explicitly set
-    <literal>-std=...</literal> when compiling (i.e. the package
-    assumes the compiler defaults to C++11 or some other standard).
-    This is a common bug in upstream build systems.</para>
 
     <para>To declare which features a package requies from the
     compiler, set either <varname>USE_CC_FEATURES</varname>
@@ -1462,6 +1455,28 @@ charconv, parallelism_ts, unique_ptr, pu
 is_trivially_copy_constructible
 </programlisting>
     </para>
+
+    <para>Language variants like <literal>gnu99</literal> and
+    <literal>c++11</literal> can be specified in <varname>FORCE_C_STD</varname>
+    and <varname>FORCE_CXX_STD</varname> if the package does not explicitly set
+    <literal>-std=...</literal> when compiling (i.e. the package
+    assumes the compiler defaults to C++11 or some other standard).
+    This is a common bug in upstream build systems.</para>
+
+    <para>Allowed values for <varname>FORCE_C_STD</varname> are
+    currently:
+<programlisting>
+c90, c99, c11, gnu90, gnu99, gnu11
+</programlisting></para>
+    </para>
+
+    <para>Allowed values for <varname>USE_CXX_FEATURES</varname> are
+    currently:
+<programlisting>
+c++03, c++11, c++14, c++17, c++20,
+gnu++03, gnu++11, gnu++14, gnu++17, gnu++20
+</programlisting></para>
+    </para>
   </sect2>
 
   <sect2 id="java-programming-language">
Index: mk/compiler.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/compiler.mk,v
retrieving revision 1.104
diff -u -p -u -r1.104 compiler.mk
--- mk/compiler.mk	29 Jul 2023 18:09:39 -0000	1.104
+++ mk/compiler.mk	29 Jul 2023 21:30:07 -0000
@@ -84,6 +84,29 @@
 #	regex, filesystem, unique_ptr, charconv, parallelism_ts,
 #	put_time, is_trivially_copy_constructible.
 #
+# FORCE_C_STD
+#
+#	Overrides the compiler's default C dialect to ensure that a
+#	specific language variant is used.  This is useful if a package
+#	uses features from a later or earlier C standard but doesn't set
+#	-std=cXX, since the default dialect choice of different compiler
+#	versions is not consistent.  It is also useful if a package
+#	wants to use GNU language extensions without setting -std=gnuXX.
+#
+#	Valid values are: c90, c99, c11, gnu90, gnu99, gnu11
+#
+# FORCE_CXX_STD
+#
+#	Overrides the compiler's default C++ dialect to ensure that a
+#	specific language variant is used.  This is useful if a package
+#	uses features from a later or earlier C++ standard but doesn't set
+#	-std=c++XX, since the default dialect choice of different compiler
+#	versions is not consistent.  It is also useful if a package
+#	wants to use GNU language extensions without setting -std=gnu++XX.
+#
+#	Valid values are: c++03, c++11, c++14, c++17, c++20, gnu++03,
+#	gnu++11, gnu++17, gnu++20
+#
 # The following variables are defined, and available for testing in
 # package Makefiles:
 #
Index: mk/compiler/gcc-style-args.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/compiler/gcc-style-args.mk,v
retrieving revision 1.1
diff -u -p -u -r1.1 gcc-style-args.mk
--- mk/compiler/gcc-style-args.mk	29 Jul 2023 17:55:47 -0000	1.1
+++ mk/compiler/gcc-style-args.mk	29 Jul 2023 21:30:07 -0000
@@ -17,6 +17,34 @@ _WRAP_EXTRA_ARGS.cc+=	-fcommon
 CWRAPPERS_PREPEND.cc+=	-fcommon
 
 #
+# Language dialects
+#
+
+_GCC_C_DIALECTS=	c90 c99 c11
+
+_GCC_C_DIALECTS+=	gnu90 gnu99 gnu11
+
+_GCC_CXX_DIALECTS=	c++03 c++11 c++14 c++17 c++20
+
+_GCC_CXX_DIALECTS+=	gnu++03 gnu++11 gnu++14 gnu++17 gnu++20
+
+.if !empty(FORCE_C_STD)
+.  for std in ${_GCC_C_DIALECTS}
+.    if !empty(FORCE_C_STD:M${std})
+CWRAPPERS_APPEND.cc+=	-std=${std}
+.    endif
+.  endfor
+.endif
+
+.if !empty(FORCE_CXX_STD)
+.  for std in ${_GCC_CXX_DIALECTS}
+.    if !empty(FORCE_CXX_STD:M${std})
+CWRAPPERS_APPEND.cxx+=	-std=${std}
+.    endif
+.  endfor
+.endif
+
+#
 # Hardening features
 #