[Clang] Workaround dependent source location issues (#106925)

[cor3ntin]

In #78436 we made some SourceLocExpr dependent to
deal with the fact that their value should reflect the name of specialized function - rather than the rtemplate in which they are first used.

However SourceLocExpr are unusual in two ways

• They don't depend on template arguments
• They morally depend on the context in which they are used (rather than called from).

It's fair to say that this is quite novels and confuses clang. In particular, in some cases, we used to create dependent SourceLocExpr and never subsequently transform them, leaving dependent objects in instantiated functions types. To work around that we avoid replacing SourceLocExpr when we think they could remain dependent. It's certainly not perfect but it fixes a number of reported bugs, and seem to only affect scenarios in which the value of the SourceLocExpr does not matter (overload resolution).

Fixes #106428
Fixes #81155
Fixes #80210
Fixes #85373

---

[llvmbot]

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

Changes

In #78436 we made some SourceLocExpr dependent to
deal with the fact that their value should reflect the name of specialized function - rather than the rtemplate in which they are first used.

However SourceLocExpr are unusual in two ways

• They don't depend on template arguments
• They morally depend on the context in which they are used (rather than called from).

It's fair to say that this is quite novels and confuses clang. In particular, in some cases, we used to create dependent SourceLocExpr and never subsequently transform them, leaving dependent objects in instantiated functions types. To work around that we avoid replacing SourceLocExpr when we think they could remain dependent. It's certainly not perfect but it fixes a number of reported bugs, and seem to only affect scenarios in which the value of the SourceLocExpr does not matter (overload resolution).

Fixes #106428
Fixes #81155
Fixes #80210
Fixes #85373

---

---

Full diff: https://github.com/llvm/llvm-project/pull/107212.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Sema/SemaExpr.cpp (+17-4)
• (modified) clang/test/SemaCXX/source_location.cpp (+60)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5eed9827343dd5..53d819c6c44574 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1121,6 +1121,8 @@ Bug Fixes to C++ Support
   Fixes (#GH85992).
 - Fixed a crash-on-invalid bug involving extraneous template parameter with concept substitution. (#GH73885)
 - Fixed assertion failure by skipping the analysis of an invalid field declaration. (#GH99868)
+- Fix an issue with dependent source location expressions (#GH106428), (#GH81155), (#GH80210), (#GH85373)
+
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index edb8b79a2220ba..f56ca398cda81c 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -5430,11 +5430,24 @@ struct EnsureImmediateInvocationInDefaultArgs
 
   // Rewrite to source location to refer to the context in which they are used.
   ExprResult TransformSourceLocExpr(SourceLocExpr *E) {
-    if (E->getParentContext() == SemaRef.CurContext)
+    DeclContext *DC = E->getParentContext();
+    if (DC == SemaRef.CurContext)
       return E;
-    return getDerived().RebuildSourceLocExpr(E->getIdentKind(), E->getType(),
-                                             E->getBeginLoc(), E->getEndLoc(),
-                                             SemaRef.CurContext);
+
+    // FIXME: During instantiation, because the rebuild of defaults arguments
+    // is not always done in the context of the template instantiator,
+    // we run the risk of producing a dependent source location
+    // that would never be rebuilt.
+    // This usually happens during overload resolution, or in contexts
+    // where the value of the source location does not matter.
+    // However, we should find a better way to deal with source location
+    // of function templates.
+    if (!SemaRef.CurrentInstantiationScope ||
+        !SemaRef.CurContext->isDependentContext() || DC->isDependentContext())
+      DC = SemaRef.CurContext;
+
+    return getDerived().RebuildSourceLocExpr(
+        E->getIdentKind(), E->getType(), E->getBeginLoc(), E->getEndLoc(), DC);
   }
 };
 
diff --git a/clang/test/SemaCXX/source_location.cpp b/clang/test/SemaCXX/source_location.cpp
index 6b3610d703e716..34177bfe287fc3 100644
--- a/clang/test/SemaCXX/source_location.cpp
+++ b/clang/test/SemaCXX/source_location.cpp
@@ -929,3 +929,63 @@ void test() {
 }
 
 }
+
+namespace GH106428 {
+
+struct add_fn {
+    template <typename T>
+    constexpr auto operator()(T lhs, T rhs,
+                              const std::source_location loc = std::source_location::current())
+        const -> T
+    {
+        return lhs + rhs;
+    }
+};
+
+
+template <class _Fp, class... _Args>
+decltype(_Fp{}(0, 0))
+__invoke(_Fp&& __f);
+
+template<typename T>
+struct type_identity { using type = T; };
+
+template<class Fn>
+struct invoke_result : type_identity<decltype(__invoke(Fn{}))> {};
+
+using i = invoke_result<add_fn>::type;
+static_assert(__is_same(i, int));
+
+}
+
+#if __cplusplus >= 202002L
+
+namespace GH81155 {
+struct buff {
+  buff(buff &, const char * = __builtin_FUNCTION());
+};
+
+template <class Ty>
+Ty declval();
+
+template <class Fx>
+auto Call(buff arg) -> decltype(Fx{}(arg));
+
+template <typename>
+struct F {};
+
+template <class Fx>
+struct InvocableR : F<decltype(Call<Fx>(declval<buff>()))> {
+  static constexpr bool value = false;
+};
+
+template <class Fx, bool = InvocableR<Fx>::value>
+void Help(Fx) {}
+
+void Test() {
+  Help([](buff) {});
+}
+
+}
+
+#endif

[AaronBallman]

LGTM

[github-actions]

@cor3ntin (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.