Re: [PATCH] c++: print source code in print_instantiation_partial_context_line

[Patrick Palka <ppalka@redhat.com>]

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On Tue, 3 Oct 2023, David Malcolm wrote:

> As mentioned in my Cauldron talk, this patch adds a call to
> diagnostic_show_locus to the "required from here" messages
> in print_instantiation_partial_context_line, so that e.g., rather
> than the rather mystifying:
> 
> In file included from ../x86_64-pc-linux-gnu/libstdc++-v3/include/memory:78,
>                  from ../../src/demo-1.C:1:
> ../x86_64-pc-linux-gnu/libstdc++-v3/include/bits/unique_ptr.h: In instantiation of ‘std::__detail::__unique_ptr_t<_Tp> std::make_unique(_Args&& ...) [with _Tp = bar; _Args = {}; __detail::__unique_ptr_t<_Tp> = __detail::__unique_ptr_t<bar>]’:
> ../../src/demo-1.C:15:32:   required from here
> ../x86_64-pc-linux-gnu/libstdc++-v3/include/bits/unique_ptr.h:1066:30: error: no matching function for call to ‘bar::bar()’
>  1066 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
>       |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../../src/demo-1.C:10:3: note: candidate: ‘bar::bar(int)’
>    10 |   bar (int);
>       |   ^~~
> ../../src/demo-1.C:10:3: note:   candidate expects 1 argument, 0 provided
> ../../src/demo-1.C:7:7: note: candidate: ‘constexpr bar::bar(const bar&)’
>     7 | class bar : public foo
>       |       ^~~
> ../../src/demo-1.C:7:7: note:   candidate expects 1 argument, 0 provided
> ../../src/demo-1.C:7:7: note: candidate: ‘constexpr bar::bar(bar&&)’
> ../../src/demo-1.C:7:7: note:   candidate expects 1 argument, 0 provided
> 
> we emit:
> 
> In file included from ../x86_64-pc-linux-gnu/libstdc++-v3/include/memory:78,
>                  from ../../src/demo-1.C:1:
> ../x86_64-pc-linux-gnu/libstdc++-v3/include/bits/unique_ptr.h: In instantiation of ‘std::__detail::__unique_ptr_t<_Tp> std::make_unique(_Args&& ...) [with _Tp = bar; _Args = {}; __detail::__unique_ptr_t<_Tp> = __detail::__unique_ptr_t<bar>]’:
> ../../src/demo-1.C:15:32:   required from here
>    15 |   return std::make_unique<bar> ();
>       |          ~~~~~~~~~~~~~~~~~~~~~~^~
> ../x86_64-pc-linux-gnu/libstdc++-v3/include/bits/unique_ptr.h:1066:30: error: no matching function for call to ‘bar::bar()’
>  1066 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
>       |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../../src/demo-1.C:10:3: note: candidate: ‘bar::bar(int)’
>    10 |   bar (int);
>       |   ^~~
> ../../src/demo-1.C:10:3: note:   candidate expects 1 argument, 0 provided
> ../../src/demo-1.C:7:7: note: candidate: ‘constexpr bar::bar(const bar&)’
>     7 | class bar : public foo
>       |       ^~~
> ../../src/demo-1.C:7:7: note:   candidate expects 1 argument, 0 provided
> ../../src/demo-1.C:7:7: note: candidate: ‘constexpr bar::bar(bar&&)’
> ../../src/demo-1.C:7:7: note:   candidate expects 1 argument, 0 provided
> 
> which shows the code that's leading to the error (the bad call to
> std::make_unique).

This is great!  I noticed however that the source code gets printed in a
surprising way in some contexts.  Consider:

template<class T> void f(typename T::type);

int main() {
  f<int>(0);
}

For this testcase we emit:

testcase.C: In function ‘int main()’:
testcase.C:4:9: error: no matching function for call to ‘f<int>(int)’
    4 |   f<int>(0);
      |   ~~~~~~^~~
testcase.C:1:24: note: candidate: ‘template<class T> void f(typename T::type)’
    1 | template<class T> void f(typename T::type);
      |                        ^
testcase.C:1:24: note:   template argument deduction/substitution failed:
testcase.C: In substitution of ‘template<class T> void f(typename T::type) [with T = int]’:
testcase.C:4:9:   required from here
testcase.C:1:24: note:     4 |   f<int>(0);
testcase.C:1:24: note:       |   ~~~~~~^~~
testcase.C:1:24: error: ‘int’ is not a class, struct, or union type
    1 | template<class T> void f(typename T::type);
      |                        ^

In particular the source code part following the "required from here" line

testcase.C:4:9:   required from here
testcase.C:1:24: note:     4 |   f<int>(0);
testcase.C:1:24: note:       |   ~~~~~~^~~

seems off, I would have expected it be

testcase.C:4:9:   required from here
    4 |   f<int>(0);
      |   ~~~~~~^~~

i.e. without the "testcase.C:1:24: note:  " prefix.  Does this look
expected?  (I also wonder if we might want to omit printing the source
code altogether in this case, since we already printed that same line
earlier during the "no matching function" error?)

> 
> 
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
> 
> OK for trunk?
> 
> 
> gcc/cp/ChangeLog:
> 	* error.cc (print_instantiation_partial_context_line): Call
> 	diagnostic_show_locus.
> 
> gcc/testsuite/ChangeLog:
> 	* g++.dg/diagnostic/static_assert3.C: Add directives for
> 	additional source printing.
> 	* g++.dg/template/error60.C: New test.
> 
> Signed-off-by: David Malcolm <dmalcolm@redhat.com>
> ---
>  gcc/cp/error.cc                               |  2 +
>  .../g++.dg/diagnostic/static_assert3.C        |  7 +++-
>  gcc/testsuite/g++.dg/template/error60.C       | 37 +++++++++++++++++++
>  3 files changed, 45 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/template/error60.C
> 
> diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc
> index ef96e140f24..767478cf5fd 100644
> --- a/gcc/cp/error.cc
> +++ b/gcc/cp/error.cc
> @@ -3774,6 +3774,8 @@ print_instantiation_partial_context_line (diagnostic_context *context,
>  		   ? _("recursively required from here\n")
>  		   : _("required from here\n"));
>      }
> +  gcc_rich_location rich_loc (loc);
> +  diagnostic_show_locus (context, &rich_loc, DK_NOTE);
>  }
>  
>  /* Same as print_instantiation_full_context but less verbose.  */
> diff --git a/gcc/testsuite/g++.dg/diagnostic/static_assert3.C b/gcc/testsuite/g++.dg/diagnostic/static_assert3.C
> index 5d363884508..4ec53f17120 100644
> --- a/gcc/testsuite/g++.dg/diagnostic/static_assert3.C
> +++ b/gcc/testsuite/g++.dg/diagnostic/static_assert3.C
> @@ -5,6 +5,11 @@
>  template <typename T, typename U> struct is_same { static constexpr bool value = false; };
>  template <typename T> struct is_same<T, T> { static constexpr bool value = true; };
>  
> +/* { dg-begin-multiline-output "" }
> +  f(0, 1.3);
> +  ~^~~~~~~~
> +   { dg-end-multiline-output "" } */
> +
>  template <typename T, typename U>
>  void f(T, U)
>  {
> @@ -32,5 +37,5 @@ void f(T, U)
>  
>  void g()
>  {
> - f(0, 1.3);
> + f(0, 1.3); // { dg-message " required from here" }
>  }
> diff --git a/gcc/testsuite/g++.dg/template/error60.C b/gcc/testsuite/g++.dg/template/error60.C
> new file mode 100644
> index 00000000000..8c2139b207c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/error60.C
> @@ -0,0 +1,37 @@
> +// { dg-options "-fdiagnostics-show-caret" }
> +
> +template <typename Foo>
> +struct my_pointer
> +{
> +  my_pointer (Foo *ptr) // { dg-message " initializing argument 1" }
> +  : m_ptr (ptr)
> +  {}
> +
> +  Foo *m_ptr;
> +};
> +
> +template <typename Foo>
> +void test (Foo val)
> +{
> +  my_pointer<Foo> ptr (val); // { dg-error "invalid conversion from 'int' to 'int\\*'" }
> +}
> +
> +void usage ()
> +{
> +  test<int> (42); // { dg-message " required from here" }
> +  /* { dg-begin-multiline-output "" }
> +   test<int> (42);
> +   ~~~~~~~~~~^~~~
> +     { dg-end-multiline-output "" } */
> +}
> +
> +  /* { dg-begin-multiline-output "" }
> +   my_pointer (Foo *ptr)
> +               ~~~~~^~~
> +     { dg-end-multiline-output "" } */
> +  /* { dg-begin-multiline-output "" }
> +   my_pointer<Foo> ptr (val);
> +                        ^~~
> +                        |
> +                        int
> +     { dg-end-multiline-output "" } */
> -- 
> 2.26.3
> 
>