[clangd] Fix a semantic-highlighting crash.

[kadircet]

thanks!

clang-tools-extra/clangd/SemanticHighlighting.cpp

664–666

can you add a comment here saying getMethodDecl can return nullptr with member pointers.

(it's also quite surprising that this is the only place we're calling getMethodDecl in clangd, afaict).

664–666

nit: isa_and_present is the new alternative

clang-tools-extra/clangd/SemanticHighlighting.cpp

if (auto *TI = D->getNameInfo().getNamedTypeInfo()) {
       H.addExtraModifier(Loc, HighlightingModifier::Declaration);
       if (D->isThisDeclarationADefinition())
         H.addExtraModifier(Loc, HighlightingModifier::Definition);
     }
     return true;
   }
 
   bool VisitCXXMemberCallExpr(CXXMemberCallExpr *CE) {
-    if (isa<CXXDestructorDecl>(CE->getMethodDecl())) {
+    // getMethodDecl can return nullptr with member pointers, e.g.
+    // `(foo.*pointer_to_member_fun)(arg);`
+    if (isa_and_present<CXXDestructorDecl>(CE->getMethodDecl())) {
       if (auto *ME = dyn_cast<MemberExpr>(CE->getCallee())) {
         if (auto *TI = ME->getMemberNameInfo().getNamedTypeInfo()) {
           H.addExtraModifier(TI->getTypeLoc().getBeginLoc(),
                              HighlightingModifier::ConstructorOrDestructor);
         }
       }
     }
     return true;

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

)cpp",
         struct $Class_def[[S]] : public $Class[[Base]] {};
         template <>
         struct $Class_def[[S]]<void> : public $Class[[Base]] {};
 
         template <typename $TemplateParameter_def[[T]]>
         $TemplateParameter[[T]] $Variable_def[[x]] = {};
         template <>
         int $Variable_def[[x]]<int> = (int)sizeof($Class[[Base]]);
+      )cpp",
+      // no crash
+      R"cpp(
+        struct $Class_def[[Foo]] {
+          void $Method_decl[[foo]]();
+        };
+
+        void $Function_def[[s]]($Class[[Foo]] $Parameter_def[[f]]) {
+          auto $LocalVariable_def[[k]] = &$Class[[Foo]]::$Method[[foo]];
+          ($Parameter[[f]].*$LocalVariable[[k]])(); // no crash on VisitCXXMemberCallExpr
+        }
       )cpp"};
   for (const auto &TestCase : TestCases)
     // Mask off scope modifiers to keep the tests manageable.
     // They're tested separately.
     checkHighlightings(TestCase, {}, ~ScopeModifierMask);
 
   checkHighlightings(R"cpp(
     class $Class_def[[A]] {