[clang] Compute accurate begin location for CallExpr with explicit object parameter (#117841)

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

Fixes #116335

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

@@ -15575,7 +15575,7 @@ 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 &)'
 }
 }