[clang] Compute accurate begin location for CallExpr with explicit object parameter

The explicit object parameter is written before the callee expression,
so the begin location should come from the explicit object parameter.

Author: HighCommander4

clang-tools-extra/clangd/unittests/XRefsTests.cpp

@@ -1019,6 +1019,15 @@ TEST(LocateSymbol, All) {
           void *Value;
           void *getPointer() const { return Info::get^Pointer(Value); }
         };
+      )cpp",
+      R"cpp(// Deducing this
+        struct S {
+          int bar(this S&);
+        };
+        void foo() {
+          S [[waldo]];
+          int x = wa^ldo.bar();
+        }
     )cpp"};
   for (const char *Test : Tests) {
     Annotations T(Test);
@@ -1035,6 +1044,7 @@ TEST(LocateSymbol, All) {
     TU.Code = std::string(T.code());
 
     TU.ExtraArgs.push_back("-xobjective-c++");
+    TU.ExtraArgs.push_back("-std=c++23");
 
     auto AST = TU.build();
     auto Results = locateSymbolAt(AST, T.point());

clang/lib/AST/Expr.cpp

@@ -1639,11 +1639,19 @@ SourceLocation CallExpr::getBeginLoc() const {
   if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(this))
     return OCE->getBeginLoc();
 
+  if (const auto *Method =
+          dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());
+      Method && Method->isExplicitObjectMemberFunction()) {
+    assert(getNumArgs() > 0 && getArg(0));
+    return getArg(0)->getBeginLoc();
+  }
+
   SourceLocation begin = getCallee()->getBeginLoc();
   if (begin.isInvalid() && getNumArgs() > 0 && getArg(0))
     begin = getArg(0)->getBeginLoc();
   return begin;
 }
+
 SourceLocation CallExpr::getEndLoc() const {
   if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(this))
     return OCE->getEndLoc();

clang/lib/Sema/SemaOverload.cpp

@@ -15565,7 +15565,7 @@ ExprResult Sema::BuildCallToMemberFunction(Scope *S, Expr *MemExprE,
     // Build the actual expression node.
     ExprResult FnExpr =
         CreateFunctionRefExpr(*this, Method, FoundDecl, MemExpr,
-                              HadMultipleCandidates, MemExpr->getBeginLoc());
+                              HadMultipleCandidates, MemExpr->getExprLoc());
     if (FnExpr.isInvalid())
       return ExprError();
 

clang/test/AST/ast-dump-cxx2b-deducing-this.cpp

@@ -9,7 +9,7 @@ int main() {
   S s;
   int x = s.f();
   // CHECK: CallExpr 0x{{[^ ]*}} <col:11, col:15> 'int
-  // CHECK-NEXT: |-ImplicitCastExpr 0x{{[^ ]*}} <col:11> 'int (*)(S &)' <FunctionToPointerDecay>
-  // CHECK-NEXT: | `-DeclRefExpr 0x{{[^ ]*}} <col:11> 'int (S &)' lvalue CXXMethod 0x{{[^ ]*}} 'f' 'int (S &)'
+  // CHECK-NEXT: |-ImplicitCastExpr 0x{{[^ ]*}} <col:13> 'int (*)(S &)' <FunctionToPointerDecay>
+  // CHECK-NEXT: | `-DeclRefExpr 0x{{[^ ]*}} <col:13> 'int (S &)' lvalue CXXMethod 0x{{[^ ]*}} 'f' 'int (S &)'
 }
 }