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Make module std; and module std.compat; work with Clang #5982

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Make module std; and module std.compat; work with Clang #5982

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5c99c5f
Add Clang diagnostic pragmas in standard library modules
cpplearner Jan 1, 2026
c56c792
Workaround LLVM-37969
cpplearner Jan 2, 2026
f4d12c2
Workaround LLVM-158341
cpplearner Jan 2, 2026
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12 changes: 12 additions & 0 deletions stl/modules/std.compat.ixx
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@@ -1,6 +1,14 @@
// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

module;

#ifdef __clang__
#pragma clang diagnostic push
// warning: 'std' is a reserved name for a module [-Wreserved-module-identifier]
#pragma clang diagnostic ignored "-Wreserved-module-identifier"
#endif // defined(__clang__)

export module std.compat;

export import std;
Expand Down Expand Up @@ -531,3 +539,7 @@ export using std::towlower;
export using std::towupper;
export using std::towctrans;
export using std::wctrans;

#ifdef __clang__
#pragma clang diagnostic pop
#endif // defined(__clang__)
14 changes: 14 additions & 0 deletions stl/modules/std.ixx
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Expand Up @@ -34,6 +34,17 @@ module;
// <intrin.h> defines some types outside of `extern "C"` or `extern "C++"`.
#include <intrin.h>

#ifdef __clang__
#include <malloc.h> // TRANSITION, LLVM-37969

#pragma clang diagnostic push
// warning: '#include <filename>' attaches the declarations to the named module 'std', which is not usually intended;
// consider moving that directive before the module declaration [-Winclude-angled-in-module-purview]
// warning: 'std' is a reserved name for a module [-Wreserved-module-identifier]
#pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
#pragma clang diagnostic ignored "-Wreserved-module-identifier"
#endif // defined(__clang__)

export module std;

#pragma warning(push)
Expand Down Expand Up @@ -155,3 +166,6 @@ export module std;
#include <cwctype>

#pragma warning(pop)
#ifdef __clang__
#pragma clang diagnostic pop
#endif // defined(__clang__)
6 changes: 6 additions & 0 deletions tests/std/include/test_header_units_and_modules.hpp
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Expand Up @@ -284,6 +284,7 @@ void test_future() {
assert(f.get() == 1729);
}

#if !(defined(__clang__) && defined(_M_ARM64EC)) // TRANSITION, LLVM-158341
#if TEST_STANDARD >= 23
void test_generator() {
using namespace std;
Expand All @@ -297,6 +298,7 @@ void test_generator() {
assert(ranges::equal(some_ints(bound), views::iota(0, bound)));
}
#endif // TEST_STANDARD >= 23
#endif // ^^^ no workaround ^^^

void test_initializer_list() {
using namespace std;
Expand Down Expand Up @@ -755,7 +757,9 @@ constexpr bool impl_test_source_location() {
using namespace std;
const auto sl = source_location::current();
assert(sl.line() == __LINE__ - 1);
#ifndef __clang__
assert(sl.column() == 38);
#endif // !defined(__clang__)

#ifdef __EDG__
assert(sl.function_name() == "bool impl_test_source_location()"sv);
Expand Down Expand Up @@ -1198,9 +1202,11 @@ void all_cpp_header_tests() {
test_fstream();
test_functional();
test_future();
#if !(defined(__clang__) && defined(_M_ARM64EC)) // TRANSITION, LLVM-158341
#if TEST_STANDARD >= 23
test_generator();
#endif // TEST_STANDARD >= 23
#endif // ^^^ no workaround ^^^
test_initializer_list();
test_iomanip();
test_ios();
Expand Down
17 changes: 14 additions & 3 deletions tests/std/tests/P2465R3_standard_library_modules/custom_format.py
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Expand Up @@ -21,10 +21,21 @@ def getBuildSteps(self, test, litConfig, shared):
test4Cpp = os.path.join(sourceDir, 'test4.cpp')
classicCpp = os.path.join(sourceDir, 'classic.cpp')

# Dependency order is important here:
inputPaths = [stdIxx, stdCompatIxx, testCpp, test2Cpp, test3Cpp, test4Cpp, classicCpp]
moduleUnits = [stdIxx, stdCompatIxx]
traditionalUnits = [testCpp, test2Cpp, test3Cpp, test4Cpp, classicCpp]

cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
if 'clang' in test.cxx:
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The Clang detection is case-sensitive ('clang' in test.cxx). Elsewhere in the lit harness the compiler is identified case-insensitively (see tests/utils/stl/test/tests.py using casefold()), so this can fail to recognize Clang for differently-cased paths and skip the --precompile steps. Please make the check case-insensitive (preferably using os.path.basename(test.cxx).casefold()) or key off the existing clang feature.

Suggested change
if 'clang' in test.cxx:
if 'clang' in os.path.basename(test.cxx).casefold():

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@cpplearner cpplearner Apr 29, 2026

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Suggested change
if 'clang' in test.cxx:
if 'clang' in test.config.available_features:

for modulePath in moduleUnits:
cmd = [test.cxx, '-x', 'c++-module', modulePath, '--precompile', *test.flags, *test.compileFlags]
yield TestStep(cmd, shared.execDir, shared.env, False)

inputPaths = ['-x', 'c++-module', *moduleUnits, '-x', 'none', *traditionalUnits]
cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
else:
# Dependency order is important here:
inputPaths = [*moduleUnits, *traditionalUnits]

cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]

if TestType.COMPILE in test.testType:
cmd += ['/c']
Expand Down
17 changes: 14 additions & 3 deletions tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
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Expand Up @@ -15,9 +15,20 @@ ()
my $stdIxx = "$stlModulesDir\\std.ixx";
my $stdCompatIxx = "$stlModulesDir\\std.compat.ixx";

# Dependency order is important here:
my @inputPaths = ($stdIxx, $stdCompatIxx, "test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");
my @moduleUnits = ($stdIxx, $stdCompatIxx);
my @traditionalUnits = ("test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");

Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
if ($ENV{PM_COMPILER} =~ m/clang/) {
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This Clang detection is case-sensitive ($ENV{PM_COMPILER} =~ m/clang/). If PM_COMPILER is set to a differently-cased value/path, the Clang module precompile path will be skipped and the build will likely fail. Consider using a case-insensitive regex (/clang/i).

Suggested change
if ($ENV{PM_COMPILER} =~ m/clang/) {
if ($ENV{PM_COMPILER} =~ m/clang/i) {

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for my $modulePath (@moduleUnits) {
Run::ExecuteCL("-x c++-module $modulePath --precompile");
}

Run::ExecuteCL(join(" ", "-x", "c++-module", @moduleUnits, "-x", "none", @traditionalUnits, "/Fe$cwd.exe"));
} else {
# Dependency order is important here:
my @inputPaths = ($stdIxx, $stdCompatIxx, "test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");

Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
}
}
1
13 changes: 10 additions & 3 deletions tests/std/tests/VSO_1775715_user_defined_modules/custom_format.py
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Expand Up @@ -15,10 +15,17 @@ def getBuildSteps(self, test, litConfig, shared):
sourceDir = os.path.dirname(testCpp)
userIxx = os.path.join(sourceDir, 'user.ixx')

# Dependency order is important here:
inputPaths = [userIxx, testCpp]
if 'clang' in test.cxx:
cmd = [test.cxx, '-x', 'c++-module', userIxx, '--precompile', *test.flags, *test.compileFlags]
yield TestStep(cmd, shared.execDir, shared.env, False)
Comment on lines +18 to +20
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The Clang detection is case-sensitive ('clang' in test.cxx). tests/utils/stl/test/tests.py treats compiler names case-insensitively (via casefold()), so this can mis-detect Clang if the compiler path contains different casing (e.g. Clang-cl.exe) and then skip the required --precompile steps. Consider switching to a case-insensitive check (e.g. based on os.path.basename(test.cxx).casefold()) or using the existing clang feature instead of substring matching.

See below for a potential fix:

        compiler_name = os.path.basename(test.cxx).casefold()

        if 'clang' in compiler_name:

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@cpplearner cpplearner Apr 29, 2026

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Yeah there's an existing feature.

Suggested change
if 'clang' in test.cxx:
cmd = [test.cxx, '-x', 'c++-module', userIxx, '--precompile', *test.flags, *test.compileFlags]
yield TestStep(cmd, shared.execDir, shared.env, False)
if 'clang' in test.config.available_features:
cmd = [test.cxx, '-x', 'c++-module', userIxx, '--precompile', *test.flags, *test.compileFlags]
yield TestStep(cmd, shared.execDir, shared.env, False)


cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
inputPaths = ['-x', 'c++-module', userIxx, '-x', 'none', testCpp]
cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
else:
# Dependency order is important here:
inputPaths = [userIxx, testCpp]

cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]

if TestType.COMPILE in test.testType:
cmd += ['/c']
Expand Down
11 changes: 8 additions & 3 deletions tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
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Expand Up @@ -10,9 +10,14 @@ ()
{
my $cwd = Run::GetCWDName();

# Dependency order is important here:
my @inputPaths = ("user.ixx", "test.cpp");
if ($ENV{PM_COMPILER} =~ m/clang/) {
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This Clang detection is case-sensitive ($ENV{PM_COMPILER} =~ m/clang/). If PM_COMPILER is provided with different casing (e.g. an absolute path with Clang-cl.exe), the Clang-specific module build steps will be skipped. Consider using a case-insensitive regex (/clang/i) to make the detection robust.

Suggested change
if ($ENV{PM_COMPILER} =~ m/clang/) {
if ($ENV{PM_COMPILER} =~ m/clang/i) {

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Run::ExecuteCL("-x c++-module user.ixx --precompile");
Run::ExecuteCL("-x c++-module user.ixx -x none test.cpp /Fe$cwd.exe");
} else {
# Dependency order is important here:
my @inputPaths = ("user.ixx", "test.cpp");

Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
}
}
1
29 changes: 18 additions & 11 deletions tests/std/tests/modules_20_matrix.lst
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Expand Up @@ -3,18 +3,25 @@

RUNALL_INCLUDE ..\..\universal_prefix.lst
RUNALL_CROSSLIST
* PM_CL="/w14365 /D_ENFORCE_FACET_SPECIALIZATIONS=1 /Zc:preprocessor"
* PM_CL="/w14365 /D_ENFORCE_FACET_SPECIALIZATIONS=1"
RUNALL_CROSSLIST
* PM_CL="/w14640 /Zc:threadSafeInit- /EHsc /DTEST_STANDARD=20 /std:c++20"
* PM_CL="/w14640 /Zc:threadSafeInit- /EHsc /DTEST_STANDARD=23 /std:c++latest"
RUNALL_CROSSLIST
* PM_CL="/MD"
* PM_CL="/MDd"
* PM_CL="/MT"
* PM_CL="/MTd"
* PM_CL="/MDd /analyze:only /analyze:autolog-"
* PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0"
* PM_CL="/MDd /utf-8"
RUNALL_CROSSLIST
PM_CL=""
ASAN PM_CL="-fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MD /Zc:preprocessor"
ASAN PM_CL="/MD /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MDd /Zc:preprocessor"
ASAN PM_CL="/MDd /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MT /Zc:preprocessor"
ASAN PM_CL="/MT /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MTd /Zc:preprocessor"
ASAN PM_CL="/MTd /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MDd /analyze:only /analyze:autolog- /Zc:preprocessor"
ASAN PM_CL="/MDd /analyze:only /analyze:autolog- /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0 /Zc:preprocessor"
ASAN PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0 /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_CL="/MDd /utf-8 /Zc:preprocessor"
ASAN PM_CL="/MDd /utf-8 /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MD"
PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MTd"
PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MT"