[libc++][modules] Adds module testing.

This adds a new module test infrastructure. This requires tagging tests
using modules. The test runner uses this information to determine the
compiler flags needed to build and use the module.

Currently modules are build per test, which allows testing them for
tests with ADDITIONAL_COMPILE_FLAGS. At the moment only 4 tests use
modules. Therefore the performance penalty is not measurable. If in the
future more tests use modules it would be good to measure the overhead
and determine whether it's acceptable.

Author: mordante

libcxx/docs/TestingLibcxx.rst

@@ -394,7 +394,7 @@ Custom Directives
 ~~~~~~~~~~~~~~~~~
 
 Lit has many directives built in (e.g., ``DEFINE``, ``UNSUPPORTED``). In addition to those directives, libc++ adds two additional libc++-specific directives that makes
-writing tests easier. See `libc++-specific Lit Directives`_ for more information about the ``FILE_DEPENDENCIES`` and ``ADDITIONAL_COMPILE_FLAGS`` libc++-specific directives.
+writing tests easier. See `libc++-specific Lit Directives`_ for more information about the ``FILE_DEPENDENCIES``, ``ADDITIONAL_COMPILE_FLAGS``, and ``MODULE_DEPENDENCIES`` libc++-specific directives.
 
 .. _libc++-specific Lit Directives:
 .. list-table:: libc++-specific Lit Directives
@@ -417,6 +417,13 @@ writing tests easier. See `libc++-specific Lit Directives`_ for more information
      - The additional compiler flags specified by a space-separated list to the ``ADDITIONAL_COMPILE_FLAGS`` libc++-specific Lit directive will be added to the end of the ``%{compile_flags}``
        substitution for the test that contains it. This libc++-specific Lit directive makes it possible to add special compilation flags without having to resort to writing a ``.sh.cpp`` test (see
        `Lit Meaning of libc++ Test Filenames`_), more powerful but perhaps overkill.
+   * - ``MODULE_DEPENDENCIES``
+     - ``// MODULE_DEPENDENCIES: std std.compat``
+     - This directive will build the required C++23 standard library
+       modules and add the additional compiler flags in
+       %{compile_flags}. (Libc++ offers these modules in C++20 as an
+       extension.)
+
 
 Benchmarks
 ==========

libcxx/test/libcxx/module_std.gen.py

@@ -30,6 +30,7 @@
     "%{test-tools}/clang_tidy_checks/libcxx-tidy.plugin",
     "%{cxx}",
     "%{flags} %{compile_flags}",
+    "std",
 )
 
 

libcxx/test/libcxx/module_std_compat.gen.py

@@ -30,6 +30,7 @@
     "%{test-tools}/clang_tidy_checks/libcxx-tidy.plugin",
     "%{cxx}",
     "%{flags} %{compile_flags}",
+    "std.compat",
 )
 
 

libcxx/test/libcxx/selftest/modules/no-modules.sh.cpp

@@ -0,0 +1,14 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Make sure that the compile flags contain no module information.
+
+// MODULE_DEPENDENCIES:
+
+// RUN: echo "%{compile_flags}" | grep -v "std.pcm"
+// RUN: echo "%{compile_flags}" | grep -v "std.compat.pcm"

libcxx/test/libcxx/selftest/modules/std-and-std.compat-module.sh.cpp

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
+
+// XFAIL: has-no-cxx-module-support
+
+// Make sure that the compile flags contain the expected elements.
+// The tests only look for the expected components and not the exact flags.
+// Otherwise changing the location of the module would break this test.
+
+// MODULE_DEPENDENCIES: std std.compat
+
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std=.*/std.pcm .*/std.pcm"
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std.compat=.*/std.compat.pcm .*/std.compat.pcm"

libcxx/test/libcxx/selftest/modules/std-module.sh.cpp

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
+
+// XFAIL: has-no-cxx-module-support
+
+// Make sure that the compile flags contain the expected elements.
+// The tests only look for the expected components and not the exact flags.
+// Otherwise changing the location of the module would break this test.
+
+// MODULE_DEPENDENCIES: std
+
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std=.*/std.pcm .*/std.pcm"
+
+// The std module should not provide the std.compat module
+// RUN: echo "%{compile_flags}" | grep -v "std.compat.pcm"

libcxx/test/libcxx/selftest/modules/std.compat-module.sh.cpp

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
+
+// XFAIL: has-no-cxx-module-support
+
+// Make sure that the compile flags contain the expected elements.
+// The tests only look for the expected components and not the exact flags.
+// Otherwise changing the location of the module would break this test.
+
+// MODULE_DEPENDENCIES: std.compat
+
+// RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std.compat=.*/std.compat.pcm .*/std.compat.pcm"
+
+// It's unspecified whether std.compat is built on the std module.
+// Therefore don't test its presence

libcxx/test/std/modules/std.compat.pass.cpp

@@ -8,11 +8,14 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
 
-// XFAIL: *
+// XFAIL: has-no-cxx-module-support
 
 // A minimal test to validate import works.
 
+// MODULE_DEPENDENCIES: std.compat
+
 import std.compat;
 
 int main(int, char**) { return !(::strlen("Hello modular world") == 19); }

libcxx/test/std/modules/std.pass.cpp

@@ -8,11 +8,14 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 // UNSUPPORTED: clang-modules-build
+// UNSUPPORTED: gcc
 
-// XFAIL: *
+// XFAIL: has-no-cxx-module-support
 
 // A minimal test to validate import works.
 
+// MODULE_DEPENDENCIES: std
+
 import std;
 
 int main(int, char**) {

libcxx/utils/libcxx/test/config.py

@@ -16,6 +16,10 @@ def _getSubstitution(substitution, config):
     raise ValueError("Substitution {} is not in the config.".format(substitution))
 
 
+def _appendToSubstitution(substitutions, key, value):
+    return [(k, v + " " + value) if k == key else (k, v) for (k, v) in substitutions]
+
+
 def configure(parameters, features, config, lit_config):
     note = lambda s: lit_config.note("({}) {}".format(config.name, s))
     config.environment = dict(os.environ)

libcxx/utils/libcxx/test/features.py

@@ -317,6 +317,18 @@ def _getAndroidDeviceApi(cfg):
             AddSubstitution("%{clang-tidy}", lambda cfg: _getSuitableClangTidy(cfg))
         ],
     ),
+    # Whether module support for the platform is available.
+    Feature(
+        name="has-no-cxx-module-support",
+        # The libc of these platforms have functions with internal linkage.
+        # This is not allowed per C11 7.1.2 Standard headers/6
+        #  Any declaration of a library function shall have external linkage.
+        when=lambda cfg: "__ANDROID__" in compilerMacros(cfg)
+        or "__PICOLIBC__" in compilerMacros(cfg)
+        or platform.system().lower().startswith("aix")
+        # Avoid building on platforms that don't support modules properly.
+        or not hasCompileFlag(cfg, "-Wno-reserved-module-identifier"),
+    ),
 ]
 
 # Deduce and add the test features that that are implied by the #defines in

libcxx/utils/libcxx/test/format.py

@@ -7,6 +7,7 @@
 # ===----------------------------------------------------------------------===##
 
 import lit
+import libcxx.test.config as config
 import lit.formats
 import os
 import re
@@ -52,6 +53,14 @@ def _executeScriptInternal(test, litConfig, commands):
     return (out, err, exitCode, timeoutInfo, parsedCommands)
 
 
+def _validateModuleDependencies(modules):
+    for m in modules:
+        if m not in ("std", "std.compat"):
+            raise RuntimeError(
+                f"Invalid module dependency '{m}', only 'std' and 'std.compat' are valid"
+            )
+
+
 def parseScript(test, preamble):
     """
     Extract the script from a test, with substitutions applied.
@@ -91,6 +100,8 @@ def parseScript(test, preamble):
     # Parse the test file, including custom directives
     additionalCompileFlags = []
     fileDependencies = []
+    modules = []  # The enabled modules
+    moduleCompileFlags = []  # The compilation flags to use modules
     parsers = [
         lit.TestRunner.IntegratedTestKeywordParser(
             "FILE_DEPENDENCIES:",
@@ -102,6 +113,11 @@ def parseScript(test, preamble):
             lit.TestRunner.ParserKind.SPACE_LIST,
             initial_value=additionalCompileFlags,
         ),
+        lit.TestRunner.IntegratedTestKeywordParser(
+            "MODULE_DEPENDENCIES:",
+            lit.TestRunner.ParserKind.SPACE_LIST,
+            initial_value=modules,
+        ),
     ]
 
     # Add conditional parsers for ADDITIONAL_COMPILE_FLAGS. This should be replaced by first
@@ -132,12 +148,53 @@ def parseScript(test, preamble):
     script += scriptInTest
 
     # 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
-    ]
+    # Modules need to be built with the same compilation flags as the
+    # test. So add these flags before adding the modules.
+    substitutions = config._appendToSubstitution(
+        substitutions, "%{compile_flags}", " ".join(additionalCompileFlags)
+    )
+
+    if modules:
+        _validateModuleDependencies(modules)
+
+        # The moduleCompileFlags are added to the %{compile_flags}, but
+        # the modules need to be built without these flags. So expand the
+        # %{compile_flags} eagerly and hardcode them in the build script.
+        compileFlags = config._getSubstitution("%{compile_flags}", test.config)
+
+        # 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 "std.compat" in modules:
+            script.insert(
+                0,
+                "%dbg(MODULE std.compat) %{cxx} %{flags} "
+                f"{compileFlags} "
+                "-Wno-reserved-module-identifier -Wno-reserved-user-defined-literal "
+                "--precompile -o %T/std.compat.pcm -c %{module}/std.compat.cppm",
+            )
+            moduleCompileFlags.extend(
+                ["-fmodule-file=std.compat=%T/std.compat.pcm", "%T/std.compat.pcm"]
+            )
+
+        # Make sure the std module is built before std.compat. Libc++'s
+        # std.compat module depends on the 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.
+        script.insert(
+            0,
+            "%dbg(MODULE std) %{cxx} %{flags} "
+            f"{compileFlags} "
+            "-Wno-reserved-module-identifier -Wno-reserved-user-defined-literal "
+            "--precompile -o %T/std.pcm -c %{module}/std.cppm",
+        )
+        moduleCompileFlags.extend(["-fmodule-file=std=%T/std.pcm", "%T/std.pcm"])
+
+        # Add compile flags required for the modules.
+        substitutions = config._appendToSubstitution(
+            substitutions, "%{compile_flags}", " ".join(moduleCompileFlags)
+        )
 
     # Perform substitutions in the script itself.
     script = lit.TestRunner.applySubstitutions(

libcxx/utils/libcxx/test/modules.py

@@ -113,20 +113,21 @@ class module_test_generator:
     clang_tidy_plugin: str
     compiler: str
     compiler_flags: str
+    module: str
 
     def write_lit_configuration(self):
         print(
             f"""\
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: clang-modules-build
 
-// XFAIL: *
-
 // REQUIRES: has-clang-tidy
 
 // The GCC compiler flags are not always compatible with clang-tidy.
 // UNSUPPORTED: gcc
 
+// MODULE_DEPENDENCIES: {self.module}
+
 // RUN: echo -n > {self.tmp_prefix}.all_partitions
 """
         )