[clangd] PopulateSwitch: disable on dependent enums.

If the enum is a dependent type, we would crash somewhere in
getIntWidth(). -Wswitch diagnostic doesn't work on dependent enums
either.

Differential Revision: https://reviews.llvm.org/D92051

clang-tools-extra/clangd/refactor/tweaks/PopulateSwitch.cpp

@@ -126,7 +126,7 @@ bool PopulateSwitch::prepare(const Selection &Sel) {
     return false;
 
   EnumD = EnumT->getDecl();
-  if (!EnumD)
+  if (!EnumD || EnumD->isDependentType())
     return false;
 
   // We trigger if there are any values in the enum that aren't covered by the

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

@@ -3084,6 +3084,12 @@ TEST_F(PopulateSwitchTest, Test) {
           R""(enum Enum {A,B,b=B}; ^switch (A) {case A:case B:break;})"",
           "unavailable",
       },
+      {
+          // Enum is dependent type
+          File,
+          R""(template<typename T> void f() {enum Enum {A}; ^switch (A) {}})"",
+          "unavailable",
+      },
   };
 
   for (const auto &Case : Cases) {