[llvm-branch-commits] [libcxx] [libc++][modules] Adds module testing. (PR #76246)

[Will Hawkins via llvm-branch-commits]

================
@@ -131,13 +138,62 @@ def parseScript(test, preamble):
     script += preamble
     script += scriptInTest
 
+    has_std_module = False
+    has_std_compat_module = False
+    for module in modules:
+        if module == "std":
+            has_std_module = True
+        elif module == "std.compat":
+            has_std_compat_module = True
+        else:
+             script.insert(0, f"echo \"The module '{module}' is not valid, use 'std' or 'std.compat'\"")
+             script.insert(1, "false");
+             return script
+
+    if modules:
+        # This flag is needed for both modules.
+        moduleCompileFlags.append("-fprebuilt-module-path=%T")
+
+        # Building the modules needs to happen before the other script commands
+        # are executed. Therefore the commands are added to the front of the
+        # list.
+        if has_std_compat_module:
+            script.insert(
+                0,
+                "%dbg(MODULE std.compat) %{cxx} %{flags} %{compile_flags} "
+                "-Wno-reserved-module-identifier -Wno-reserved-user-defined-literal "
+                "--precompile -o %T/std.compat.pcm -c %{module}/std.compat.cppm",
+            )
+            moduleCompileFlags.append("%T/std.compat.pcm")
+
+        # Make sure the std module is added before std.compat.
+        # Libc++'s std.compat module will depend on its std module.
+        # It is not known whether the compiler expects the modules in the order
+        # of their dependencies. However it's trivial to provide them in that
+        # order.
+        if has_std_module:
+            script.insert(
+                0,
+                "%dbg(MODULE std) %{cxx} %{flags} %{compile_flags} "
+                "-Wno-reserved-module-identifier -Wno-reserved-user-defined-literal "
+                "--precompile -o %T/std.pcm -c %{module}/std.cppm",
+            )
+            moduleCompileFlags.append("%T/std.pcm")
+
     # Add compile flags specified with ADDITIONAL_COMPILE_FLAGS.
     substitutions = [
         (s, x + " " + " ".join(additionalCompileFlags))
         if s == "%{compile_flags}"
         else (s, x)
         for (s, x) in substitutions
     ]
+    # In order to use modules additional compilation flags are required.
----------------
hawkinsw wrote:

```suggestion
    # In order to use modules, additional compilation flags are required.
```

https://github.com/llvm/llvm-project/pull/76246