[llvm-bugs] [Bug 37191] New: Clang unable to diagnose missing template keyword when unrelated code is added.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37191

            Bug ID: 37191
           Summary: Clang unable to diagnose missing template keyword when
                    unrelated code is added.
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rtrieu at google.com
                CC: llvm-bugs at lists.llvm.org

Clang is able to diagnose a missing template keyword for good-diagnostic.cc
below.  However, if some unrelated code is added as in bad-diagnostic.cc below,
an incorrect diagnostic about overloaded functions is emitted instead.


$ cat good-diagnostic.cc 
template <typename T, int N>
struct Foo {
  template <int Shift>
  static void bar(T arr[N]) {}
};

template <typename T, int Width, int Stride>
void test() {
  T in[Width];
  Foo<T, Width>::bar<Stride>(in);
}

void run() {
  test<int, 10, 10>();
}
$ clang good-diagnostic.cc 
good-diagnostic.cc:10:3: error: missing 'template' keyword prior to dependent
      template name 'bar'
  Foo<T, Width>::bar<Stride>(in);
  ^
good-diagnostic.cc:14:3: note: in instantiation of function template
      specialization 'test<int, 10, 10>' requested here
  test<int, 10, 10>();
  ^
1 error generated.




$ cat bad-diagnostic.cc 
struct S {};

bool run(const S a, const S b);

bool operator< (const S &s1, const S &s2) { return run(s1, s2); }
bool operator>=(const S &s1, const S &s2) { return run(s1, s2); }
bool operator<=(const S &s1, const S &s2) { return run(s1, s2); }

template <typename T, int N>
struct Foo {
  template <int Shift>
  static void bar(T arr[N]) {}
};

template <typename T, int Width, int Stride>
void test() {
  T in[Width];
  Foo<T, Width>::bar<Stride>(in);
}

void run() {
  test<int, 10, 10>();
}
$ clang bad-diagnostic.cc 
bad-diagnostic.cc:18:3: error: reference to overloaded function could not be
      resolved; did you mean to call it?
  Foo<T, Width>::bar<Stride>(in);
  ^~~~~~~~~~~~~~~~~~
bad-diagnostic.cc:22:3: note: in instantiation of function template
      specialization 'test<int, 10, 10>' requested here
  test<int, 10, 10>();
  ^
bad-diagnostic.cc:12:15: note: possible target for call
  static void bar(T arr[N]) {}
              ^
1 error generated.

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