[clang] Reapply "[Clang][Sema] Diagnose function/variable templates that shadow their own template parameters (#78274)" (PR #79683)
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Sat Jan 27 01:11:58 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Krystian Stasiowski (sdkrystian)
<details>
<summary>Changes</summary>
Reapplies #<!-- -->78274 with the addition of a default-error warning (`strict-primary-template-shadow`) that is issued for instances of shadowing which were previously accepted prior to this patch.
---
Full diff: https://github.com/llvm/llvm-project/pull/79683.diff
6 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+1)
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+3)
- (modified) clang/include/clang/Sema/Sema.h (+1-1)
- (modified) clang/lib/Sema/SemaDecl.cpp (+22-9)
- (modified) clang/lib/Sema/SemaTemplate.cpp (+6-3)
- (modified) clang/test/CXX/temp/temp.res/temp.local/p6.cpp (+18-4)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5330cd9caad801..24d3ada5bfd9df 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -97,6 +97,7 @@ Attribute Changes in Clang
Improvements to Clang's diagnostics
-----------------------------------
+- Clang now diagnoses function/variable templates that shadow their own template parameters, e.g. ``template<class T> void T();``.
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 649de9f47c4619..4e3b20548913ab 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4966,6 +4966,9 @@ def err_template_param_shadow : Error<
"declaration of %0 shadows template parameter">;
def ext_template_param_shadow : ExtWarn<
err_template_param_shadow.Summary>, InGroup<MicrosoftTemplateShadow>;
+def ext_compat_template_param_shadow : ExtWarn<
+ err_template_param_shadow.Summary>, InGroup<
+ DiagGroup<"strict-primary-template-shadow">>, DefaultError;
def note_template_param_here : Note<"template parameter is declared here">;
def note_template_param_external : Note<
"template parameter from hidden source: %0">;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 1f1cbd11ff7358..5c148db48140ed 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -8256,7 +8256,7 @@ class Sema final {
TemplateSpecializationKind TSK,
bool Complain = true);
- void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl);
+ void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl, bool IssueWarning = false);
TemplateDecl *AdjustDeclIfTemplate(Decl *&Decl);
NamedDecl *ActOnTypeParameter(Scope *S, bool Typename,
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index f9bf1d14bdc4f6..de65b3c09c28cf 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6377,12 +6377,6 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
} else if (DiagnoseUnexpandedParameterPack(NameInfo, UPPC_DeclarationType))
return nullptr;
- // The scope passed in may not be a decl scope. Zip up the scope tree until
- // we find one that is.
- while ((S->getFlags() & Scope::DeclScope) == 0 ||
- (S->getFlags() & Scope::TemplateParamScope) != 0)
- S = S->getParent();
-
DeclContext *DC = CurContext;
if (D.getCXXScopeSpec().isInvalid())
D.setInvalidType();
@@ -6506,12 +6500,25 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
RemoveUsingDecls(Previous);
}
- if (Previous.isSingleResult() &&
- Previous.getFoundDecl()->isTemplateParameter()) {
+ // if (Previous.isSingleResult() &&
+ // Previous.getFoundDecl()->isTemplateParameter()) {
+ if (auto *TPD = Previous.getAsSingle<NamedDecl>(); TPD && TPD->isTemplateParameter()) {
+ // Older versions of clang allowed the names of function/variable templates
+ // to shadow the names of their template parameters. For the compatibility purposes
+ // we detect such cases and issue a default-to-error warning that can be disabled with
+ // -fno-strict-primary-template-shadow.
+ bool IssueShadowingWarning = false;
+ for (Scope *Inner = S; (Inner->getFlags() & Scope::DeclScope) == 0 ||
+ Inner->isTemplateParamScope(); Inner = Inner->getParent()) {
+ if (IssueShadowingWarning = Inner->isDeclScope(TPD))
+ break;
+ }
+
// Maybe we will complain about the shadowed template parameter.
if (!D.isInvalidType())
DiagnoseTemplateParameterShadow(D.getIdentifierLoc(),
- Previous.getFoundDecl());
+ TPD,
+ IssueShadowingWarning);
// Just pretend that we didn't see the previous declaration.
Previous.clear();
@@ -6535,6 +6542,12 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
if (getLangOpts().CPlusPlus)
CheckExtraCXXDefaultArguments(D);
+ // The scope passed in may not be a decl scope. Zip up the scope tree until
+ // we find one that is.
+ while ((S->getFlags() & Scope::DeclScope) == 0 ||
+ (S->getFlags() & Scope::TemplateParamScope) != 0)
+ S = S->getParent();
+
NamedDecl *New;
bool AddToScope = true;
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9bfa71dc8bcf1d..4ba8dfc19d2f6d 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -885,7 +885,7 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
/// that the template parameter 'PrevDecl' is being shadowed by a new
/// declaration at location Loc. Returns true to indicate that this is
/// an error, and false otherwise.
-void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl) {
+void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl, bool IssueWarning) {
assert(PrevDecl->isTemplateParameter() && "Not a template parameter");
// C++ [temp.local]p4:
@@ -893,8 +893,11 @@ void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl) {
// scope (including nested scopes).
//
// Make this a warning when MSVC compatibility is requested.
- unsigned DiagId = getLangOpts().MSVCCompat ? diag::ext_template_param_shadow
- : diag::err_template_param_shadow;
+ unsigned DiagId = getLangOpts().MSVCCompat
+ ? diag::ext_template_param_shadow
+ : (IssueWarning
+ ? diag::ext_compat_template_param_shadow
+ : diag::err_template_param_shadow);
const auto *ND = cast<NamedDecl>(PrevDecl);
Diag(Loc, DiagId) << ND->getDeclName();
NoteTemplateParameterLocation(*ND);
diff --git a/clang/test/CXX/temp/temp.res/temp.local/p6.cpp b/clang/test/CXX/temp/temp.res/temp.local/p6.cpp
index e2aa0ff344291d..00bb35813c39af 100644
--- a/clang/test/CXX/temp/temp.res/temp.local/p6.cpp
+++ b/clang/test/CXX/temp/temp.res/temp.local/p6.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify %s -fcxx-exceptions -std=c++1y
+// RUN: %clang_cc1 -verify %s -fcxx-exceptions -std=c++1y -Wno-error=strict-primary-template-shadow
namespace N {}
@@ -127,16 +127,30 @@ template<int T> struct Z { // expected-note 16{{declared here}}
template<typename T> // expected-note {{declared here}}
void f(int T) {} // expected-error {{declaration of 'T' shadows template parameter}}
-// FIXME: These are ill-formed: a template-parameter shall not have the same name as the template name.
namespace A {
template<typename T> struct T {}; // expected-error{{declaration of 'T' shadows template parameter}}
// expected-note at -1{{template parameter is declared here}}
+ template<typename T> struct U {
+ template<typename V> struct V {}; // expected-error{{declaration of 'V' shadows template parameter}}
+ // expected-note at -1{{template parameter is declared here}}
+ };
}
namespace B {
- template<typename T> void T() {}
+ template<typename T> void T() {} // expected-warning{{declaration of 'T' shadows template parameter}}
+ // expected-note at -1{{template parameter is declared here}}
+
+ template<typename T> struct U {
+ template<typename V> void V(); // expected-warning{{declaration of 'V' shadows template parameter}}
+ // expected-note at -1{{template parameter is declared here}}
+ };
}
namespace C {
- template<typename T> int T;
+ template<typename T> int T; // expected-warning{{declaration of 'T' shadows template parameter}}
+ // expected-note at -1{{template parameter is declared here}}
+ template<typename T> struct U {
+ template<typename V> static int V; // expected-warning{{declaration of 'V' shadows template parameter}}
+ // expected-note at -1{{template parameter is declared here}}
+ };
}
namespace PR28023 {
``````````
</details>
https://github.com/llvm/llvm-project/pull/79683
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