Duplicate explicit template instantiation reports incorrect source location

[llvmbot]

Bugzilla Link	13858
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor

Extended Description

Sometimes the note for the "previous explicit instantiation" refers to an implicit instantiation instead of the explicit one. For example, take this as test.cpp:

template <typename T>
struct S {
};

void foo() {
    S<int>();
}

template struct S<int>;
template struct S<int>;

Actual Results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:6:5: note: previous explicit instantiation is here
    S<int>();
    ^
1 error generated.

Expected results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:9:17: note: previous explicit instantiation is here
template struct S<int>;
                ^
1 error generated.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (llvmbot)

| | | | --- | --- | | Bugzilla Link | [13858](https://llvm.org/bz13858) | | Version | trunk | | OS | All | | Reporter | LLVM Bugzilla Contributor |

Extended Description

Sometimes the note for the "previous explicit instantiation" refers to an implicit instantiation instead of the explicit one. For example, take this as test.cpp:

template <typename T>
struct S {
};

void foo() {
    S<int>();
}

template struct S<int>;
template struct S<int>;

Actual Results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:6:5: note: previous explicit instantiation is here
    S<int>();
    ^
1 error generated.

Expected results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:9:17: note: previous explicit instantiation is here
template struct S<int>;
                ^
1 error generated.

[shafik]

CC @AaronBallman

[llvmbot]

@llvm/issue-subscribers-c-1

Author: None (llvmbot)

| | | | --- | --- | | Bugzilla Link | [13858](https://llvm.org/bz13858) | | Version | trunk | | OS | All | | Reporter | LLVM Bugzilla Contributor |

Extended Description

Sometimes the note for the "previous explicit instantiation" refers to an implicit instantiation instead of the explicit one. For example, take this as test.cpp:

template <typename T>
struct S {
};

void foo() {
    S<int>();
}

template struct S<int>;
template struct S<int>;

Actual Results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:6:5: note: previous explicit instantiation is here
    S<int>();
    ^
1 error generated.

Expected results:

$ clang -c test.cpp
test.cpp:10:17: error: duplicate explicit instantiation of 'S<int>'
template struct S<int>;
                ^
test.cpp:9:17: note: previous explicit instantiation is here
template struct S<int>;
                ^
1 error generated.

[Maetveis]

The diagnostic might even refer to an explicit declaration as in the following example:

template <typename T>
struct S {
    void f(){};
};

extern template void S<int>::f();

template struct S<int>;
template void S<int>::f();

Note the extern in extern template.

<source>:9:23: error: duplicate explicit instantiation of 'f'
    9 | template void S<int>::f();
      |                       ^
<source>:6:30: note: previous explicit instantiation is here
    6 | extern template void S<int>::f();
      |                              ^

Expected:

<source>:9:23: error: duplicate explicit instantiation of 'f'
    9 | template void S<int>::f();
      |                       ^
<source>:8:17: note: previous explicit instantiation is here
    8 | template struct S<int>;
      |                 ^

See this example on Compiler Explorer