backends: apply per-subproject language args to targets

Compile and link args were collected via CoreData.get_external_args()
and get_external_link_args(), which build an OptionKey without a
subproject. Per-subproject values such as -Dsub:c_args=-DFOO or c_args
in the default_options of a subproject() call were stored as augments
in the option store but never consulted, so they silently never reached
the compile or link command.

Resolve the value per target with the existing augment- and
override-aware CoreData.get_option_for_target() at the three
target-context call sites. As a side effect, <lang>_args and
<lang>_link_args entries in a target's override_options now take
effect as well.

Fixes #13260.

docs/markdown/snippets/subproject_lang_args.md

@@ -0,0 +1,15 @@
+## Per-subproject language arguments are now applied
+
+Compiler and linker arguments set for a specific subproject, for example
+`-Dsub:c_args=-DFOO` on the command line or `c_args` in the
+`default_options` of a `subproject()` call, are now added to the compile
+and link commands of that subproject's targets. Previously such values
+were accepted and stored but silently ignored.
+
+Similarly, `<lang>_args` and `<lang>_link_args` entries in a target's
+`override_options` now take effect.
+
+In all cases the per-subproject or per-target value replaces the global
+value (including flags coming from environment variables such as
+`CFLAGS`), it is not appended to it. This matches what
+`get_option('c_args')` already returned inside a subproject.

mesonbuild/backend/backends.py

@@ -1027,8 +1027,11 @@ class Backend:
         commands += self.build.get_global_args(compiler, target)
         # Compile args added from the env: CFLAGS/CXXFLAGS, etc, or the cross
         # file. We want these to override all the defaults, but not the
-        # per-target compile args.
-        commands += self.environment.coredata.get_external_args(target.for_machine, compiler.get_language())
+        # per-target compile args. Resolved per target so that per-subproject
+        # values (-Dsub:c_args=...) are honoured.
+        ext_args = self.environment.coredata.get_option_for_target(target, f'{compiler.get_language()}_args')
+        assert isinstance(ext_args, list), 'for mypy'
+        commands += ext_args
         # Using both /Z7 or /ZI and /Zi at the same times produces a compiler warning.
         # We do not add /Z7 or /ZI by default. If it is being used it is because the user has explicitly enabled it.
         # /Zi needs to be removed in that case to avoid cl's warning to that effect (D9025 : overriding '/Zi' with '/ZI')

mesonbuild/build.py

@@ -1939,7 +1939,9 @@ class BuildTarget(Target):
         args: T.List[str] = []
         for lang in LANGUAGES_USING_LDFLAGS:
             try:
-                args += self.environment.coredata.get_external_link_args(self.for_machine, lang)
+                largs = self.environment.coredata.get_option_for_target(self, f'{lang}_link_args')
+                assert isinstance(largs, list), 'for mypy'
+                args += largs
             except KeyError:
                 pass
         return self.get_rpath_dirs_from_link_args(args)

mesonbuild/compilers/compilers.py

@@ -1195,9 +1195,13 @@ class Compiler(HoldableObject, metaclass=SimpleABC):
         # Link args added using add_global_link_arguments() override
         # per-project link arguments.  Link args added from the env (LDFLAGS)
         # override all the defaults but not the per-target link args.
+        # Resolved per target so that per-subproject values
+        # (-Dsub:c_link_args=...) are honoured.
+        ext_link_args = self.environment.coredata.get_option_for_target(target, f'{self.get_language()}_link_args')
+        assert isinstance(ext_link_args, list), 'for mypy'
         return build.get_project_link_args(self, target) \
             + build.get_global_link_args(self, target) \
-            + self.environment.coredata.get_external_link_args(self.for_machine, self.get_language())
+            + ext_link_args
 
     def get_target_link_args(self, target: 'BuildTarget') -> T.List[str]:
         return target.link_args

test cases/common/98 subproject subdir/subprojects/subsubsub-1.0/.meson-subproject-wrap-hash.txt

@@ -0,0 +1 @@
+0fd8007dd44a1a5eb5c01af4c138f0993c6cb44da194b36db04484212eff591b

test cases/common/98 subproject subdir/subprojects/subsubsub-1.0/meson.build

@@ -0,0 +1,3 @@
+project('subsubsub')
+
+meson.override_dependency('subsubsub', declare_dependency())

test cases/common/98 subproject subdir/subprojects/subsubsub.wrap

@@ -0,0 +1,2 @@
+[wrap-redirect]
+filename = sub_implicit/subprojects/subsub/subprojects/subsubsub.wrap

test cases/unit/139 subproject lang args/meson.build

@@ -0,0 +1,6 @@
+project('top', 'c')
+
+subproject('sub')
+
+static_library('top', 'top.c')
+static_library('over', 'over.c', override_options: ['c_args=-DOVERRIDE_FLAG'])

test cases/unit/139 subproject lang args/over.c

@@ -0,0 +1,7 @@
+#ifndef OVERRIDE_FLAG
+#error "OVERRIDE_FLAG not set"
+#endif
+
+int over(void) {
+    return 0;
+}

test cases/unit/139 subproject lang args/subprojects/sub/meson.build

@@ -0,0 +1,3 @@
+project('sub', 'c')
+
+static_library('sub', 'sub.c')

test cases/unit/139 subproject lang args/subprojects/sub/sub.c

@@ -0,0 +1,7 @@
+#ifndef SUB_FLAG
+#error "SUB_FLAG not set"
+#endif
+
+int sub(void) {
+    return 0;
+}

test cases/unit/139 subproject lang args/top.c

@@ -0,0 +1,7 @@
+#ifndef TOP_FLAG
+#error "TOP_FLAG not set"
+#endif
+
+int top(void) {
+    return 0;
+}

unittests/allplatformstests.py

@@ -3462,6 +3462,23 @@ class AllPlatformTests(BasePlatformTests):
         self.build()
         self.run_tests()
 
+    def test_subproject_lang_args(self):
+        testdir = os.path.join(self.unit_test_dir, '139 subproject lang args')
+        self.init(testdir, extra_args=['-Dc_args=-DTOP_FLAG', '-Dsub:c_args=-DSUB_FLAG'])
+        # The source files #error out if their expected flag is missing.
+        self.build()
+        # A per-subproject or per-target value replaces the global one.
+        for cmd in self.get_compdb():
+            if cmd['file'].endswith('top.c'):
+                self.assertIn('-DTOP_FLAG', cmd['command'])
+                self.assertNotIn('-DSUB_FLAG', cmd['command'])
+            elif cmd['file'].endswith('sub.c'):
+                self.assertIn('-DSUB_FLAG', cmd['command'])
+                self.assertNotIn('-DTOP_FLAG', cmd['command'])
+            elif cmd['file'].endswith('over.c'):
+                self.assertIn('-DOVERRIDE_FLAG', cmd['command'])
+                self.assertNotIn('-DTOP_FLAG', cmd['command'])
+
     def test_wipe_from_builddir(self):
         testdir = os.path.join(self.common_test_dir, '157 custom target subdir depend files')
         self.init(testdir)