[clang][Sema] Resolving Panic Caused by Inconsistent Arguments in Variadic Template Variables

When template variables are variadic, sema may panic, potentially leading to a situation
 where the number of function variables exceeds the number of template variables.
The sema compares the template signature and function signature parameters one by one,
 which can trigger an assertion error. This PR, when encountering variadic templates,
avoids comparing the template signature and function signature parameters one by one.

issue: #70191

Author: knightXun

clang/docs/ReleaseNotes.rst

@@ -1069,6 +1069,9 @@ Static Analyzer
   `#65888 <https://github.com/llvm/llvm-project/pull/65888>`_, and
   `#65887 <https://github.com/llvm/llvm-project/pull/65887>`_
 
+- Resolving Inconsistent Arguments Panic in Variadic Template Variables.
+  (`#70280: <https://github.com/llvm/llvm-project/pull/70280>`_).
+
 .. _release-notes-sanitizers:
 
 Sanitizers

clang/lib/Sema/SemaOverload.cpp

@@ -11092,6 +11092,14 @@ static void DiagnoseBadConversion(Sema &S, OverloadCandidate *Cand,
       I--;
   }
 
+  bool isVariadic = false;
+  for (unsigned N = 0; N < Fn->getNumParams(); N++) {
+    if (Fn->getParamDecl(N)->isParameterPack()) {
+      isVariadic = true;
+      break;
+    }
+  }
+
   std::string FnDesc;
   std::pair<OverloadCandidateKind, OverloadCandidateSelect> FnKindPair =
       ClassifyOverloadCandidate(S, Cand->FoundDecl, Fn, Cand->getRewriteKind(),
@@ -11100,8 +11108,9 @@ static void DiagnoseBadConversion(Sema &S, OverloadCandidate *Cand,
   Expr *FromExpr = Conv.Bad.FromExpr;
   QualType FromTy = Conv.Bad.getFromType();
   QualType ToTy = Conv.Bad.getToType();
-  SourceRange ToParamRange =
-      !isObjectArgument ? Fn->getParamDecl(I)->getSourceRange() : SourceRange();
+  SourceRange ToParamRange = !isObjectArgument && !isVariadic
+                                 ? Fn->getParamDecl(I)->getSourceRange()
+                                 : SourceRange();
 
   if (FromTy == S.Context.OverloadTy) {
     assert(FromExpr && "overload set argument came from implicit argument?");

clang/test/SemaCXX/GH70280.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+namespace PR70280 {
+  typedef a; // expected-error {{a type specifier is required for all declarations}}
+  using b = char*;
+  template <typename... c> void d(c...) = d<b, a>(0, ""); // expected-error {{no matching function for call to 'd'}}
+  // expected-error@-1 {{illegal initializer (only variables can be initialized)}}
+  // expected-note@-2 {{candidate function template not viable: no known conversion from 'const char[1]' to 'a' (aka 'int') for 2nd argument}}
+}