Ensure that $lang_args and $lang_link_args are properly parsed

Currently we don't handle things correctly if we get a string we should
split, and the linker and needs compiler arguments. It would result in
two unsplit strings in a list, instead of the split arguments in a list

Fixes: #8348

mesonbuild/compilers/compilers.py

@@ -1227,22 +1227,18 @@ def get_global_options(lang: str,
     argkey = OptionKey('args', lang=lang, machine=for_machine)
     largkey = argkey.evolve('link_args')
 
-    # We shouldn't need listify here, but until we have a separate
-    # linker-driver representation and can have that do the combine we have to
-    # do it this way.
-    compile_args = mesonlib.listify(env.options.get(argkey, []))
-    link_args = mesonlib.listify(env.options.get(largkey, []))
+    cargs = coredata.UserArrayOption(
+        description + ' compiler',
+        env.options.get(argkey, []), split_args=True, user_input=True, allow_dups=True)
+    largs = coredata.UserArrayOption(
+        description + ' linker',
+        env.options.get(largkey, []), split_args=True, user_input=True, allow_dups=True)
 
+    # This needs to be done here, so that if we have string values in the env
+    # options that we can safely combine them *after* they've been split
     if comp.INVOKES_LINKER:
-        link_args = compile_args + link_args
+        largs.set_value(largs.value + cargs.value)
 
-    opts: 'KeyedOptionDictType' = {
-        argkey: coredata.UserArrayOption(
-            description + ' compiler',
-            compile_args, split_args=True, user_input=True, allow_dups=True),
-        largkey: coredata.UserArrayOption(
-            description + ' linker',
-            link_args, split_args=True, user_input=True, allow_dups=True),
-    }
+    opts: 'KeyedOptionDictType' = {argkey: cargs, largkey: largs}
 
     return opts

test cases/common/237 proper args splitting/main.c

@@ -0,0 +1,11 @@
+#ifndef FOO
+# error "FOO is not defined"
+#endif
+
+#ifndef BAR
+# error "BAR is not defined"
+#endif
+
+int main(void) {
+    return 0;
+}

test cases/common/237 proper args splitting/meson.build

@@ -0,0 +1,9 @@
+project('proper args splitting', 'c')
+
+test(
+  'main',
+  executable(
+    'main',
+    'main.c',
+  )
+)

test cases/common/237 proper args splitting/test.json

@@ -0,0 +1,9 @@
+{
+  "matrix": {
+    "options": {
+      "c_args": [
+        { "val": "-DFOO -DBAR" }
+      ]
+    }
+  }
+}