[clang] [clang][modules] Make -fmodules-decluse work on the public/private pair of modules (PR #192585)
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Thu Apr 16 19:52:39 PDT 2026
https://github.com/matts1 created https://github.com/llvm/llvm-project/pull/192585
Previously, it would only check the main module.
Now, if the main module is a private module (foo_Private), it will also
check the public module.
>From 6b72aad0ffcdbbfe688491ab32f750a1e73ada44 Mon Sep 17 00:00:00 2001
From: Matt Stark <msta at google.com>
Date: Thu, 16 Apr 2026 16:28:27 +1000
Subject: [PATCH 1/2] [clang][modules] Write test for fmodules-decluse with
private modules.
This just creates a test that shows the existing behaviour of clang, so
that it's clear what changes I'm making.
---
.../Modules/declare-use-private-textual.cpp | 69 +++++++++++++++++++
1 file changed, 69 insertions(+)
create mode 100644 clang/test/Modules/declare-use-private-textual.cpp
diff --git a/clang/test/Modules/declare-use-private-textual.cpp b/clang/test/Modules/declare-use-private-textual.cpp
new file mode 100644
index 0000000000000..92c7144559ee7
--- /dev/null
+++ b/clang/test/Modules/declare-use-private-textual.cpp
@@ -0,0 +1,69 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-strict-decluse -fmodule-name=lib_Private -I %t %t/lib.cpp -verify
+
+//--- module.modulemap
+// This simulates a modulemap that might reasonably be generated by a build system for something resembling the following.
+// This can be used to perform strict dependency checking to ensure that your build graph is correctly declared.
+// cc_library(
+// name = "lib",
+// # .cpp file in sources -> generate a compilation action with -fmodule-name=lib_Private
+// # .h file in sources -> add "textual header" to private modulemap
+// sources = ["lib.cpp"],
+// # headers -> textual header in public module
+// headers = ["lib.h"],
+// # Implementation dep -> in use of private module
+// implementation_deps = [":impl_dep"]
+// # dep -> in use of private and public module
+// deps = [":direct"],
+// )
+// cc_library(name = "direct", headers = ["direct.h"], deps = [":indirect"], ...)
+// cc_library(name = "indirect", headers = ["indirect.h"], ..)
+// cc_library(name = "impl_dep", headers = ["impl_dep.h"], ...)
+module lib_Private {
+ use impl_dep
+ use lib
+ use direct
+}
+
+module lib {
+ textual header "lib.h"
+ use direct
+}
+
+
+module impl_dep {
+ textual header "impl_dep.h"
+}
+
+module direct {
+ textual header "direct.h"
+ use indirect
+}
+
+module indirect {
+ textual header "indirect.h"
+}
+
+//--- impl_dep.h
+void impl_dep();
+//--- direct.h
+#include "impl_dep.h" // OK (it should only verify the main module).
+void direct();
+//--- indirect.h
+void indirect();
+//--- not_module.h
+void not_module();
+
+//--- lib.cpp
+#include "lib.h"
+#include "direct.h" // OK
+#include "indirect.h" // expected-error {{module lib_Private does not directly depend on a module exporting 'indirect.h', which is part of indirectly-used module indirect}}
+#include "impl_dep.h" // OK
+#include "not_module.h" // expected-error {{lib_Private does not depend on a module exporting 'not_module.h'}}
+
+//--- lib.h
+#include "direct.h" // OK
+#include "indirect.h" // OK
+#include "impl_dep.h" // OK
+#include "not_module.h" // OK
\ No newline at end of file
>From 59766087d89ba1e41569fec00b318557bf3b19c2 Mon Sep 17 00:00:00 2001
From: Matt Stark <msta at google.com>
Date: Thu, 16 Apr 2026 16:28:27 +1000
Subject: [PATCH 2/2] [clang][modules] Make -fmodules-decluse work on the
public/private pair of modules
Previously, it would only check the main module.
Now, if the main module is a private module (foo_Private), it will also
check the public module.
---
.../include/clang/Basic/DiagnosticLexKinds.td | 2 +
clang/lib/Lex/HeaderSearch.cpp | 14 +++++--
clang/lib/Lex/ModuleMap.cpp | 42 ++++++++++++++++---
.../Modules/declare-use-private-textual.cpp | 6 +--
4 files changed, 52 insertions(+), 12 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index 2846db8320275..85fa290de6fd9 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -999,6 +999,8 @@ def err_undeclared_use_of_module : Error<
"module %0 does not depend on a module exporting '%1'">;
def err_undeclared_use_of_module_indirect : Error<
"module %0 does not directly depend on a module exporting '%1', which is part of indirectly-used module %2">;
+def err_undeclared_use_of_module_private : Error<
+ "module %0 does not depend on a module exporting '%1', which is part of module %2, although its private module does">;
def warn_non_modular_include_in_framework_module : Warning<
"include of non-modular header inside framework module '%0': '%1'">,
InGroup<NonModularIncludeInFrameworkModule>, DefaultIgnore;
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 5cc2c04a68077..ecdfc701c2e22 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -58,6 +58,8 @@ ALWAYS_ENABLED_STATISTIC(NumFrameworkLookups, "Number of framework lookups.");
ALWAYS_ENABLED_STATISTIC(NumSubFrameworkLookups,
"Number of subframework lookups.");
+static constexpr StringRef ModuleMapExtension = ".modulemap";
+
const IdentifierInfo *
HeaderFileInfo::getControllingMacro(ExternalPreprocessorSource *External) {
if (LazyControllingMacro.isID()) {
@@ -2059,12 +2061,16 @@ static OptionalFileEntryRef getPrivateModuleMap(FileEntryRef File,
bool Diagnose = true) {
StringRef Filename = llvm::sys::path::filename(File.getName());
SmallString<128> PrivateFilename(File.getDir().getName());
- if (Filename == "module.map")
+ if (Filename.ends_with(ModuleMapExtension)) {
+ SmallString<128> PrivateName(Filename);
+ PrivateName.resize(PrivateName.size() - ModuleMapExtension.size());
+ PrivateName.append(".private.modulemap");
+ llvm::sys::path::append(PrivateFilename, PrivateName);
+ } else if (Filename == "module.map") {
llvm::sys::path::append(PrivateFilename, "module_private.map");
- else if (Filename == "module.modulemap")
- llvm::sys::path::append(PrivateFilename, "module.private.modulemap");
- else
+ } else {
return std::nullopt;
+ }
auto PMMFile = FileMgr.getOptionalFileRef(PrivateFilename);
if (PMMFile) {
if (Diagnose && Filename == "module.map")
diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 56ae51ada7148..e78c6693cbd10 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -46,6 +46,8 @@
using namespace clang;
+static constexpr llvm::StringRef kPrivateModuleSuffix = "_Private";
+
void ModuleMapCallbacks::anchor() {}
void ModuleMap::resolveLinkAsDependencies(Module *Mod) {
@@ -498,10 +500,31 @@ void ModuleMap::diagnoseHeaderInclusion(Module *RequestingModule,
// No errors for indirect modules. This may be a bit of a problem for modules
// with no source files.
- if (getTopLevelOrNull(RequestingModule) != getTopLevelOrNull(SourceModule))
- return;
+ Module *TopLevelRequestingModule = getTopLevelOrNull(RequestingModule);
+ Module *TopLevelSourceModule = getTopLevelOrNull(SourceModule);
+ bool IsPublicForMainPrivateModule = false;
+ if (TopLevelRequestingModule != TopLevelSourceModule) {
+ // Suppose we have a pair of files foo.cpp / foo.h.
+ // Our build system may want to verify that foo.cpp only uses things
+ // declared in the implementation_deps of foo, while foo.h only uses things
+ // declared in interface_deps. This requires them to be two seperate
+ // modules, foo_Private and foo. This check is required to ensure that foo.h
+ // is still checked. Otherwise, foo.h would never be checked, since it will
+ // never be the top-level module.
+ if (TopLevelRequestingModule && TopLevelSourceModule &&
+ llvm::StringRef(TopLevelSourceModule->Name)
+ .ends_with(kPrivateModuleSuffix) &&
+ llvm::StringRef(TopLevelSourceModule->Name)
+ .drop_back(kPrivateModuleSuffix.size()) ==
+ TopLevelRequestingModule->Name) {
+ IsPublicForMainPrivateModule = true;
+ } else {
+ return;
+ }
+ }
bool Excluded = false;
+ bool UsedByPrivateModule = false;
Module *Private = nullptr;
Module *NotUsed = nullptr;
@@ -524,6 +547,9 @@ void ModuleMap::diagnoseHeaderInclusion(Module *RequestingModule,
if (RequestingModule && LangOpts.ModulesDeclUse &&
!RequestingModule->directlyUses(Header.getModule())) {
NotUsed = Header.getModule();
+ if (IsPublicForMainPrivateModule) {
+ UsedByPrivateModule = SourceModule->directlyUses(Header.getModule());
+ }
continue;
}
@@ -543,9 +569,15 @@ void ModuleMap::diagnoseHeaderInclusion(Module *RequestingModule,
// We have found a module, but we don't use it.
if (NotUsed) {
- Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module_indirect)
- << RequestingModule->getTopLevelModule()->Name << Filename
- << NotUsed->Name;
+ if (UsedByPrivateModule) {
+ Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module_private)
+ << RequestingModule->getTopLevelModule()->Name << Filename
+ << NotUsed->Name << SourceModule->Name;
+ } else {
+ Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module_indirect)
+ << RequestingModule->getTopLevelModule()->Name << Filename
+ << NotUsed->Name;
+ }
return;
}
diff --git a/clang/test/Modules/declare-use-private-textual.cpp b/clang/test/Modules/declare-use-private-textual.cpp
index 92c7144559ee7..c030e2afa6e6d 100644
--- a/clang/test/Modules/declare-use-private-textual.cpp
+++ b/clang/test/Modules/declare-use-private-textual.cpp
@@ -64,6 +64,6 @@ void not_module();
//--- lib.h
#include "direct.h" // OK
-#include "indirect.h" // OK
-#include "impl_dep.h" // OK
-#include "not_module.h" // OK
\ No newline at end of file
+#include "indirect.h" // expected-error {{module lib does not directly depend on a module exporting 'indirect.h', which is part of indirectly-used module indirect}}
+#include "impl_dep.h" // expected-error {{module lib does not depend on a module exporting 'impl_dep.h', which is part of module impl_dep, although its private module does}}
+#include "not_module.h" // expected-error {{module lib does not depend on a module exporting 'not_module.h'}}
\ No newline at end of file
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