Split environment variable and command line cflags

They are supposed to have different behavior. The environment variables
apply to both the compiler and linker when the compiler acts as a
linker, but the command line ones do not.

Fixes #8345

1 files changed, 22 insertions, 1 deletions

diff --git a/mesonbuild/environment.py b/mesonbuild/environment.py
index f59eb87..373c063 100644
--- a/mesonbuild/environment.py
+++ b/mesonbuild/environment.py
@@ -798,7 +798,11 @@ class Environment:
 
         env_opts: T.DefaultDict[OptionKey, T.List[str]] = collections.defaultdict(list)
 
-        for (evar, keyname), for_machine in itertools.product(opts, MachineChoice):
+        if self.is_cross_build():
+            for_machine = MachineChoice.BUILD
+        else:
+            for_machine = MachineChoice.HOST
+        for evar, keyname in opts:
             p_env = _get_env_var(for_machine, self.is_cross_build(), evar)
             if p_env is not None:
                 # these may contain duplicates, which must be removed, else
@@ -834,6 +838,23 @@ class Environment:
                             env_opts[key].extend(p_list)
                     else:
                         key = OptionKey.from_string(keyname).evolve(machine=for_machine)
+                        if evar in compilers.compilers.CFLAGS_MAPPING.values():
+                            # If this is an environment variable, we have to
+                            # store it separately until the compiler is
+                            # instantiated, as we don't know whether the
+                            # compiler will want to use these arguments at link
+                            # time and compile time (instead of just at compile
+                            # time) until we're instantiating that `Compiler`
+                            # object. This is required so that passing
+                            # `-Dc_args=` on the command line and `$CFLAGS`
+                            # have subtely differen behavior. `$CFLAGS` will be
+                            # added to the linker command line if the compiler
+                            # acts as a linker driver, `-Dc_args` will not.
+                            #
+                            # We stil use the original key as the base here, as
+                            # we want to inhert the machine and the compiler
+                            # language
+                            key = key.evolve('env_args')
                         env_opts[key].extend(p_list)
 
         # Only store options that are not already in self.options,