[clangd] Move the selection decltype hack to getSourceRange.

[hokein]

Summary

Previously, it was in canSafelySkipNode, which is only used to decide
whether we should descend into it and its children, and we still used
the incomplete Decltypeloc.getSourceRange() to claim tokens, which will
cause some tokens were not claimed correctly.

Separate a change of https://reviews.llvm.org/D116536

clang-tools-extra/clangd/Selection.cpp

for (const auto *N = Common; N; N = N->Parent) {
     }
   }
   if (Common)
     SelectionUsedRecovery.record(0, LanguageLabel); // unused.
 }
 
 // Return the range covering a node and all its children.
 SourceRange getSourceRange(const DynTypedNode &N) {
+  // DeclTypeTypeLoc::getSourceRange() is incomplete, which would lead to
+  // failing to descend into the child expression.
+  // decltype(2+2);
+  // ~~~~~~~~~~~~~ <-- correct range
+  // ~~~~~~~~      <-- range reported by getSourceRange()
+  // ~~~~~~~~~~~~  <-- range with this hack(i.e, missing closing paren)
+  // FIXME: Alter DecltypeTypeLoc to contain parentheses locations and get
+  // rid of this patch.
+  if (const auto *TL = N.get<TypeLoc>()) {
+    if (auto DT = TL->getAs<DecltypeTypeLoc>()) {
+      SourceRange S = DT.getSourceRange();
+      S.setEnd(DT.getUnderlyingExpr()->getEndLoc());
+      return S;
+    }
+  }
   // MemberExprs to implicitly access anonymous fields should not claim any
   // tokens for themselves. Given:
   //   struct A { struct { int b; }; };
   // The clang AST reports the following nodes for an access to b:
   //   A().b;
   //   [----] MemberExpr, base = A().<anonymous>, member = b
   //   [----] MemberExpr: base = A(), member = <anonymous>
   //   [-]    CXXConstructExpr
#endif
   // don't intersect the selection may be recursively skipped.
   bool canSafelySkipNode(const DynTypedNode &N) {
     SourceRange S = getSourceRange(N);
     if (auto *TL = N.get<TypeLoc>()) {
       // FIXME: TypeLoc::getBeginLoc()/getEndLoc() are pretty fragile
       // heuristics. We should consider only pruning critical TypeLoc nodes, to
       // be more robust.
 
-      // DeclTypeTypeLoc::getSourceRange() is incomplete, which would lead to
-      // failing
-      // to descend into the child expression.
-      // decltype(2+2);
-      // ~~~~~~~~~~~~~ <-- correct range
-      // ~~~~~~~~      <-- range reported by getSourceRange()
-      // ~~~~~~~~~~~~  <-- range with this hack(i.e, missing closing paren)
-      // FIXME: Alter DecltypeTypeLoc to contain parentheses locations and get
-      // rid of this patch.
-      if (auto DT = TL->getAs<DecltypeTypeLoc>())
-        S.setEnd(DT.getUnderlyingExpr()->getEndLoc());
       // AttributedTypeLoc may point to the attribute's range, NOT the modified
       // type's range.
       if (auto AT = TL->getAs<AttributedTypeLoc>())
         S = AT.getModifiedLoc().getSourceRange();
     }
     // SourceRange often doesn't manage to accurately cover attributes.
     // Fortunately, attributes are rare.
     if (llvm::any_of(getAttributes(N),

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

Case Cases[] = {
           "UserDefinedLiteral"},
 
       {
           R"cpp(
         int a;
         decltype([[^a]] + a) b;
         )cpp",
           "DeclRefExpr"},
+      {"[[decltype]]^(1) b;", "DecltypeTypeLoc"}, // Not the VarDecl.
 
       // Objective-C nullability attributes.
       {
           R"cpp(
             @interface I{}
             @property(nullable) [[^I]] *x;
             @end
           )cpp",