compilers: Fix output ext while compile-only on MSVC

When doing a compile-only self.compile() check, cl.exe expects an output
file of type *.obj, and passing it `output.exe` makes it write the
compiled object to `output.exe.obj`. Detect when we're doing
a compily-only check and change the suffix ourselves.

This is fine most of the time, but fails when you need to inspect the
compiled file manually.

Also store stdout/stderr on the returned object.

mesonbuild/compilers.py

@@ -441,7 +441,7 @@ class Compiler():
         return extra_flags
 
     @contextlib.contextmanager
-    def compile(self, code, extra_args=None):
+    def compile(self, code, extra_args=None, compile_only=False):
         if extra_args is None:
             extra_args = []
 
@@ -457,20 +457,25 @@ class Compiler():
 
                 # Extension only matters if running results; '.exe' is
                 # guaranteed to be executable on every platform.
-                output = os.path.join(tmpdirname, 'output.exe')
+                if compile_only:
+                    suffix = 'obj'
+                else:
+                    suffix = 'exe'
+                output = os.path.join(tmpdirname, 'output.' + suffix)
 
                 commands = self.get_exelist()
                 commands.append(srcname)
                 commands += extra_args
                 commands += self.get_output_args(output)
+                if compile_only:
+                    commands += self.get_compile_only_args()
                 mlog.debug('Running compile:')
                 mlog.debug('Working directory: ', tmpdirname)
                 mlog.debug('Command line: ', ' '.join(commands), '\n')
                 mlog.debug('Code:\n', code)
-                p, stdo, stde = Popen_safe(commands, cwd=tmpdirname)
-                mlog.debug('Compiler stdout:\n', stdo)
-                mlog.debug('Compiler stderr:\n', stde)
-
+                p, p.stdo, p.stde = Popen_safe(commands, cwd=tmpdirname)
+                mlog.debug('Compiler stdout:\n', p.stdo)
+                mlog.debug('Compiler stderr:\n', p.stde)
                 p.input_name = srcname
                 p.output_name = output
                 yield p
@@ -748,14 +753,13 @@ int main () {{
         # Add CFLAGS/CXXFLAGS/OBJCFLAGS/OBJCXXFLAGS from the env
         # We assume that the user has ensured these are compiler-specific
         args += env.coredata.external_args[self.language]
-        # We only want to compile; not link
-        args += self.get_compile_only_args()
         # Append extra_args to the compiler check args such that it overrides
         extra_args = self._override_args(self.get_compiler_check_args(), extra_args)
         extra_args = self.unix_link_flags_to_native(extra_args)
         # Append both to the compiler args such that they override them
         args = self._override_args(args, extra_args)
-        with self.compile(code, args) as p:
+        # We only want to compile; not link
+        with self.compile(code, args, compile_only=True) as p:
             return p.returncode == 0
 
     def _links_wrapper(self, code, env, extra_args, dependencies):
@@ -1408,14 +1412,16 @@ class ValaCompiler(Compiler):
     def get_output_args(self, target):
         return ['-o', target]
 
+    def get_compile_only_args(self):
+        return ['-C']
+
     def get_werror_args(self):
         return ['--fatal-warnings']
 
     def sanity_check(self, work_dir, environment):
         code = 'class MesonSanityCheck : Object { }'
         args = self.get_cross_extra_flags(environment, compile=True, link=False)
-        args += ['-C']
-        with self.compile(code, args) as p:
+        with self.compile(code, args, compile_only=True) as p:
             if p.returncode != 0:
                 msg = 'Vala compiler {!r} can not compile programs' \
                       ''.format(self.name_string())
@@ -1435,8 +1441,8 @@ class ValaCompiler(Compiler):
             code = 'class MesonFindLibrary : Object { }'
             vapi_args = ['--pkg', libname]
             args = self.get_cross_extra_flags(env, compile=True, link=False)
-            args += ['-C'] + vapi_args
-            with self.compile(code, args) as p:
+            args += vapi_args
+            with self.compile(code, args, compile_only=True) as p:
                 if p.returncode == 0:
                     return vapi_args
         # Not found? Try to find the vapi file itself.