[clangd] Enable relative configs in check mode

[kadircet]

Summary

See https://github.com/clangd/clangd/issues/649#issuecomment-885903316.
Also disables config support in lit tests to make sure tests are not affected by
clangd config files lying around.

[kadircet]

• Rebase

[sammccall]

clang-tools-extra/clangd/tool/Check.cpp

275–278

Only if FakeFile.empty() - we shouldn't take the arbitrary temp path into account

[kadircet]

• Don't use local configs for temp files

clang-tools-extra/clangd/test/check-fail.test

 // RUN: cp %s %t.cpp
-// RUN: not clangd -check=%t.cpp 2>&1 | FileCheck -strict-whitespace %s
+// RUN: not clangd -enable-config=0 -check=%t.cpp 2>&1 | FileCheck -strict-whitespace %s
 
 // CHECK: Testing on source file {{.*}}check-fail.test
 // CHECK: internal (cc1) args are: -cc1
 // CHECK: Building preamble...
 // CHECK: [pp_file_not_found] Line {{.*}}: 'missing.h' file not found
 // CHECK: Building AST...
 // CHECK: Testing features at each token
 // CHECK: tweak: ExpandAutoType ==> FAIL
 // CHECK: All checks completed, 2 errors
 
 #include "missing.h"
 void fun();
 auto x = fun;

clang-tools-extra/clangd/test/check-lines.test

 // RUN: cp %s %t.cpp
-// RUN: not clangd -check=%t.cpp -check-lines=6-14 2>&1 | FileCheck -strict-whitespace %s
-// RUN: not clangd -check=%t.cpp -check-lines=14 2>&1 | FileCheck -strict-whitespace %s
+// RUN: not clangd -enable-config=0 -check=%t.cpp -check-lines=6-14 2>&1 | FileCheck -strict-whitespace %s
+// RUN: not clangd -enable-config=0 -check=%t.cpp -check-lines=14 2>&1 | FileCheck -strict-whitespace %s
 
 // CHECK: Testing on source file {{.*}}check-lines.test
 // CHECK: internal (cc1) args are: -cc1
 // CHECK: Building preamble...
 // CHECK: Building AST...
 // CHECK: Testing features at each token
 // CHECK: tweak: ExpandAutoType ==> FAIL
 // CHECK: All checks completed, 1 errors
 
 void fun();
 auto x = fun; // This line is tested
 auto y = fun; // This line is not tested

clang-tools-extra/clangd/test/check.test

 // RUN: cp %s %t.cpp
-// RUN: clangd -log=verbose -check=%t.cpp 2>&1 | FileCheck -strict-whitespace %s
+// RUN: clangd -enable-config=0 -log=verbose -check=%t.cpp 2>&1 | FileCheck -strict-whitespace %s
 
 // CHECK: Testing on source file
 // CHECK: internal (cc1) args are: -cc1
 // CHECK: Building preamble...
 // CHECK: Built preamble
 // CHECK: Building AST...
 // CHECK: Testing features at each token
 // CHECK-DAG: tweak: ExpandAuto
 // CHECK-DAG: hover: true
 // CHECK-DAG: tweak: AddUsing
 // CHECK: All checks completed, 0 errors
 
 namespace ns {
 struct Foo {};
 } // namespace ns
 auto f = ns::Foo();

clang-tools-extra/clangd/tool/Check.cpp

Contents = R"cpp(
       size_t N = 50;
       auto xxx = std::string(N, 'x');
     )cpp";
   }
   log("Testing on source file {0}", File);
 
   auto ContextProvider = ClangdServer::createConfiguredContextProvider(
       Opts.ConfigProvider, nullptr);
-  WithContext Ctx(ContextProvider(""));
+  WithContext Ctx(ContextProvider(
+      FakeFile.empty()
+          ? File
+          : /*Don't turn on local configs for an arbitrary temp path.*/ ""));
   Checker C(File, Opts);
   if (!C.buildCommand(TFS) || !C.buildInvocation(TFS, Contents) ||
       !C.buildAST())
     return false;
   C.testLocationFeatures(ShouldCheckLine, EnableCodeCompletion);
 
   log("All checks completed, {0} errors", C.ErrCount);
   return C.ErrCount == 0;
 }
 
 } // namespace clangd
 } // namespace clang