[clangd] Fix the crash in getQualification

[kbobyrev]

Summary

Happens when DestContext is LinkageSpecDecl and hense CurContext happens to be
both not TagDecl and NamespaceDecl.

Minimal reproducer: trigger define outline in

namespace ns {
extern "C" {
typedef int foo;
}
foo Fo^o(int id) { return id; }
}

[kbobyrev]

Fix formatting

[kadircet]

thanks for chasing this down! as mentioned offline a test case like:

namespace ns {
extern "C" {
typedef int foo;
}
foo Fo^o(int id) { return id; }
}

in define outline should be enough to ensure it is WAI.

clang-tools-extra/clangd/AST.cpp

133

rather than having !NNS in the check below it might be nicer to put:

else {
// Other types of contexts cannot be spelled in code, just skip over them.
continue;
}

I believe continue makes sense, that way we can spell in cases like:

namespace ns {
extern "C" {
typedef int foo;
}
foo Foo(int id) { return id; }
}

foo should still become ns::foo in other contexts.

[kbobyrev]

Make the controol flow less confusing.

[kbobyrev]

Add test, improve docs in code.

[kadircet]

thanks, lgtm!

clang-tools-extra/clangd/AST.cpp

for (const DeclContext *CurContext = SourceContext; CurContext;
 
     NestedNameSpecifier *NNS = nullptr;
     if (auto *TD = llvm::dyn_cast<TagDecl>(CurContext)) {
       // There can't be any more tag parents after hitting a namespace.
       assert(!ReachedNS);
       (void)ReachedNS;
       NNS = NestedNameSpecifier::Create(Context, nullptr, false,
                                         TD->getTypeForDecl());
-    } else {
+    } else if (auto *NSD = llvm::dyn_cast<NamespaceDecl>(CurContext)) {
       ReachedNS = true;
-      auto *NSD = llvm::cast<NamespaceDecl>(CurContext);
       NNS = NestedNameSpecifier::Create(Context, nullptr, NSD);
-      // Anonymous and inline namespace names are not spelled while qualifying a
-      // name, so skip those.
+      // Anonymous and inline namespace names are not spelled while qualifying
+      // a name, so skip those.
       if (NSD->isAnonymousNamespace() || NSD->isInlineNamespace())
         continue;
+    } else {
+      // Other types of contexts cannot be spelled in code, just skip over
+      // them.
+      continue;
     }
     // Stop if this namespace is already visible at DestContext.
     if (IsVisible(NNS))
       break;
 
     Parents.push_back(NNS);
   }
 
   // Go over name-specifiers in reverse order to create necessary qualification,

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

std::vector<std::string> VisibleNamespaces;
               namespace ns2 {
                 void insert(); // Foo
               }
             }
           )cpp",
           {"ns2::", "ns2::", ""},
           {"ns1::"},
       },
+      {
+          R"cpp(
+            namespace ns {
+            extern "C" {
+            typedef int Foo;
+            }
+            }
+            void insert(); // ns::Foo
+          )cpp",
+          {"ns::"},
+          {},
+      },
   };
   for (const auto &Case : Cases) {
     Annotations Test(Case.Test);
     TestTU TU = TestTU::withCode(Test.code());
     ParsedAST AST = TU.build();
     std::vector<const Decl *> InsertionPoints;
     const NamedDecl *TargetDecl;
     findDecl(AST, [&](const NamedDecl &ND) {