Author: Chuanqi Xu Date: 2026-07-09T08:51:57Z New Revision: 9c747b3ed9116841c48913eb06ccb5fad13ad1a7
URL: https://github.com/llvm/llvm-project/commit/9c747b3ed9116841c48913eb06ccb5fad13ad1a7 DIFF: https://github.com/llvm/llvm-project/commit/9c747b3ed9116841c48913eb06ccb5fad13ad1a7.diff LOG: [clang] [serialization] Step into UsingShadowDecl when find existing decl (#208393) Close https://github.com/llvm/llvm-project/issues/207581 The root cause of the problem is that：enum constant decl, for which its parent is not enum class, is special. They can be accessed directly without access its parent. When modules join the game, it becomes more complex. As for members in other entities like class, we can assume the member is accessable if their parent are accesable. But it is a different story for enums. See https://github.com/llvm/llvm-project/issues/131058 for the whole story of the backrgound. Then we didn't write enum constant decl to the lookup table of its parent of parent in the ASTWriter. So that if other consumer in Sema wants to access them, they have to get it by entities like exported using decls. However, the problem is, in ASTReader, when we merge decls, we use noload_lookup to find existing decls. And the absense of unnamed enum decl in the parent of its parent's lookup table makes the merge fails. For enum constant decl in named enum, they will still have a name lookup table. So we will merge them somehow. But for enum constants in unnamed enum, they were removed from the only lookup table so the merge fails. This is the whole story of the current issue. To fix this, when we merge decls, we step into the UsingShadowDecl to find the real decls. This is fine as we never merge decls with different kinds. We can even call this a tiny optimization. Added: clang/test/Modules/GH207581.cpp Modified: clang/lib/Serialization/ASTReaderDecl.cpp Removed: ################################################################################ diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp index 25598683d1d62..f343372c3e2f4 100644 --- a/clang/lib/Serialization/ASTReaderDecl.cpp +++ b/clang/lib/Serialization/ASTReaderDecl.cpp @@ -3420,10 +3420,20 @@ ASTDeclReader::FindExistingResult::~FindExistingResult() { } /// Find the declaration that should be merged into, given the declaration found -/// by name lookup. If we're merging an anonymous declaration within a typedef, -/// we need a matching typedef, and we merge with the type inside it. +/// by name lookup. If we're not merging with a UsingShadowDecl but Found is a +/// UsingShadowDecl, we need to skip the UsingShadowDecl. If we're merging an +/// anonymous declaration within a typedef, we need a matching typedef, and we +/// merge with the type inside it. static NamedDecl *getDeclForMerging(NamedDecl *Found, - bool IsTypedefNameForLinkage) { + bool IsTypedefNameForLinkage, + bool FilteringUsingShadowDecl) { + // If the taregt declaration we want is not a UsingShadowDecl, we don't need + // to return the UsingShadowDecl at all. + if (auto *USD = dyn_cast<UsingShadowDecl>(Found); + USD && FilteringUsingShadowDecl) + return getDeclForMerging(USD->getTargetDecl(), IsTypedefNameForLinkage, + FilteringUsingShadowDecl); + if (!IsTypedefNameForLinkage) return Found; @@ -3584,7 +3594,9 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) { for (IdentifierResolver::iterator I = IdResolver.begin(Name), IEnd = IdResolver.end(); I != IEnd; ++I) { - if (NamedDecl *Existing = getDeclForMerging(*I, TypedefNameForLinkage)) + if (NamedDecl *Existing = + getDeclForMerging(*I, TypedefNameForLinkage, + /*FilteringUsingShadowDecl=*/false)) if (C.isSameEntity(Existing, D)) return FindExistingResult(Reader, D, Existing, AnonymousDeclNumber, TypedefNameForLinkage); @@ -3592,10 +3604,12 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) { } else if (DeclContext *MergeDC = getPrimaryContextForMerging(Reader, DC)) { DeclContext::lookup_result R = MergeDC->noload_lookup(Name); for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E; ++I) { - if (NamedDecl *Existing = getDeclForMerging(*I, TypedefNameForLinkage)) - if (C.isSameEntity(Existing, D)) + if (NamedDecl *Existing = getDeclForMerging(*I, TypedefNameForLinkage, + !isa<UsingShadowDecl>(D))) + if (C.isSameEntity(Existing, D)) { return FindExistingResult(Reader, D, Existing, AnonymousDeclNumber, TypedefNameForLinkage); + } } } else { // Not in a mergeable context. diff --git a/clang/test/Modules/GH207581.cpp b/clang/test/Modules/GH207581.cpp new file mode 100644 index 0000000000000..4b7c5659dd42a --- /dev/null +++ b/clang/test/Modules/GH207581.cpp @@ -0,0 +1,45 @@ +// RUN: rm -rf %t +// RUN: split-file %s %t +// +// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -emit-module-interface %t/fmt.cppm -o %t/fmt.pcm +// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -emit-module-interface %t/seastar.cppm -o %t/seastar.pcm +// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -fmodule-file=fmt=%t/fmt.pcm -fmodule-file=seastar=%t/seastar.pcm -fsyntax-only -verify %t/main.cc + +//--- base.h +#ifndef BASE_H +#define BASE_H +namespace demo { +enum { max_packed_args = 6 }; +template <bool B, class T, class F> struct cond { using type = F; }; +template <class T, class F> struct cond<true, T, F> { using type = T; }; +template <class T> struct a_t {}; +template <class T> struct b_t {}; +template <class Context, int N> +using arg_t = typename cond<(N <= max_packed_args), a_t<Context>, b_t<Context>>::type; +} +#endif + +//--- fmt.cppm +module; +#include "base.h" +export module fmt; +export namespace demo { + using demo::max_packed_args; +} + +//--- seastar.cppm +module; +#include "base.h" +export module seastar; +export namespace seastar { inline int dummy = 0; } + +//--- main.cc +// expected-no-diagnostics +import seastar; +import fmt; +#include "base.h" +int main() { + demo::arg_t<int, 5> a; + demo::arg_t<int, 7> b; + return 0; +} _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
