[Bug c++/85498] New: Unable to resolve function name with inferred return type

[gcc at dcousens dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85498

Bug ID: 85498
   Summary: Unable to resolve function name with inferred return
type
   Product: gcc
   Version: 7.3.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: gcc at dcousens dot com
  Target Milestone: ---

gcc version 7.3.1 20180312 (GCC)

But,  this fails on many different GCC versions.
https://godbolt.org/g/G5gEx2

**Expected:** Compilation should succeed (like other compilers, MSVC, Clang,
etc)

**Actual:** Compilation failed

```
template
auto foo (T t) {
return t;
}

template
void bar (const T) {}

int main () {
bar(foo);
}
```

Result:
```
: In function 'int main()':

:10:17: error: no matching function for call to 'bar()'

 bar(foo);

 ^

:7:6: note: candidate: template void bar(T)

 void bar (const T) {}

  ^~~

:7:6: note:   template argument deduction/substitution failed:

:10:17: note:   couldn't deduce template parameter 'T'

 bar(foo);

 ^

Compiler returned: 1
```

[Bug c++/85499] New: Unable to resolve function with inferred return type

[gcc at dcousens dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85499

Bug ID: 85499
   Summary: Unable to resolve function with inferred return type
   Product: gcc
   Version: 7.3.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: gcc at dcousens dot com
  Target Milestone: ---

gcc version 7.3.1 20180312 (GCC)

But,  this fails on many different GCC versions.
https://godbolt.org/g/G5gEx2

**Expected:** Compilation should succeed (like other compilers, MSVC, Clang,
etc)

**Actual:** Compilation failed

```
template
auto foo (T t) {
return t;
}

template
void bar (const T) {}

int main () {
bar(foo);
}
```

Result:
```
: In function 'int main()':

:10:17: error: no matching function for call to 'bar()'

 bar(foo);

 ^

:7:6: note: candidate: template void bar(T)

 void bar (const T) {}

  ^~~

:7:6: note:   template argument deduction/substitution failed:

:10:17: note:   couldn't deduce template parameter 'T'

 bar(foo);

 ^

Compiler returned: 1
```

[Bug c++/85499] Unable to resolve function with inferred return type

[gcc at dcousens dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85499

--- Comment #1 from gcc at dcousens dot com ---
Instantiating `foo` previously can resolve the issue,  but isn't a work-able
solution in many cases.

```
int main () {
foo(1);
bar(foo);
}
```