c++: print source code in print_instantiation_partial_context_line

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).

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>

3 files changed, 45 insertions, 1 deletions

diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc
index ef96e14..767478cf 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 5d36388..4ec53f1 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 0000000..8c2139b
--- /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 "" } */