[clangd] Fix SelectionTree to allow selection range expression in foreach loops.

[hokein]

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

275

nit: the ^ inside the string "foo" is a bit tricky, I didn't spot it at the first glance, I'd move it out of the string, e.g. mak^eStr("foo"^)

clang-tools-extra/clangd/Selection.cpp

public:
   bool TraverseQualifiedTypeLoc(QualifiedTypeLoc QX) {
     return traverseNode<TypeLoc>(
         &QX, [&] { return TraverseTypeLoc(QX.getUnqualifiedLoc()); });
   }
   // Uninteresting parts of the AST that don't have locations within them.
   bool TraverseNestedNameSpecifier(NestedNameSpecifier *) { return true; }
   bool TraverseType(QualType) { return true; }
 
+  // The DeclStmt for the loop variable claims to cover the whole range
+  // inside the parens, this causes the range-init expression to not be hit.
+  // Traverse the loop VarDecl instead, which has the right source range.
+  bool TraverseCXXForRangeStmt(CXXForRangeStmt *S) {
+    return traverseNode(S, [&] {
+      return TraverseStmt(S->getInit()) && TraverseDecl(S->getLoopVariable()) &&
+             TraverseStmt(S->getRangeInit()) && TraverseStmt(S->getBody());
+    });
+  }
+
 private:
   using Base = RecursiveASTVisitor<SelectionVisitor>;
 
   SelectionVisitor(ASTContext &AST, const syntax::TokenBuffer &Tokens,
                    const PrintingPolicy &PP, unsigned SelBegin, unsigned SelEnd,
                    FileID SelFile)
       : SM(AST.getSourceManager()), LangOpts(AST.getLangOpts()),
 #ifndef NDEBUG

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

Case Cases[] = {
       // No crash
       {
           R"cpp(
             template <class T> struct Foo {};
             template <[[template<class> class /*cursor here*/^U]]>
              struct Foo<U<int>*> {};
           )cpp",
           "TemplateTemplateParmDecl"},
+
+      // Foreach has a weird AST, ensure we can select parts of the range init.
+      // This used to fail, because the DeclStmt for C claimed the whole range.
+      {
+          R"cpp(
+            struct Str {
+              const char *begin();
+              const char *end();
+            };
+            Str makeStr(const char*);
+            void loop() {
+              for (const char* C : [[mak^eStr("f^oo")]])
+                ;
+            }
+          )cpp",
+          "CallExpr"},
   };
   for (const Case &C : Cases) {
     Annotations Test(C.Code);
     auto AST = TestTU::withCode(Test.code()).build();
     auto T = makeSelectionTree(C.Code, AST);
     EXPECT_EQ("TranslationUnitDecl", nodeKind(&T.root())) << C.Code;
 
     if (Test.ranges().empty()) {