Hello.

The patch is about splitting pair of errors into
error and inform which seems logical to me in this
situation:

/xg++ -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C:3:24: error: 
template parameter ‘class ... Args’
    3 | template<typename Fun, typename... Args> // { dg-error "template 
parameter" }
      |                        ^~~~~~~~
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C:7:8: note: 
redeclared here as ‘class Arg0’
    7 | struct call // { dg-message "note: redeclared here" }
      |        ^~~~

instead of:

g++ /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C -c
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C:3:24: error: 
template parameter ‘class ... Args’
    3 | template<typename Fun, typename... Args> // { dg-error "template 
parameter" }
      |                        ^~~~~~~~
/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp0x/vt-34314.C:7:8: error: 
redeclared here as ‘class Arg0’
    7 | struct call // { dg-message "note: redeclared here" }
      |        ^~~~

That helps -fmax-errors=1 to not split the error in the middle.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

gcc/cp/ChangeLog:

2020-01-23  Martin Liska  <mli...@suse.cz>

        PR c++/92440
        * pt.c (redeclare_class_template): Use inform
        for the second location.

gcc/testsuite/ChangeLog:

2020-01-23  Martin Liska  <mli...@suse.cz>

        PR c++/92440
        * g++.dg/template/pr92440.C: New test.
        * g++.dg/cpp0x/vt-34314.C: Update error to note.
        * g++.dg/template/pr59930-2.C: Likewise.
        * g++.old-deja/g++.pt/redecl1.C: Likewise.
---
 gcc/cp/pt.c                                 |  2 +-
 gcc/testsuite/g++.dg/cpp0x/vt-34314.C       |  6 +++---
 gcc/testsuite/g++.dg/template/pr59930-2.C   |  2 +-
 gcc/testsuite/g++.dg/template/pr92440.C     | 10 ++++++++++
 gcc/testsuite/g++.dg/template/redecl2.C     |  2 +-
 gcc/testsuite/g++.old-deja/g++.pt/redecl1.C |  4 ++--
 6 files changed, 18 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/pr92440.C


diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 4520c995028..f9bed1ea4fb 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -6149,7 +6149,7 @@ redeclare_class_template (tree type, tree parms, tree cons)
 		  != TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm)))))
 	{
 	  error ("template parameter %q+#D", tmpl_parm);
-	  error ("redeclared here as %q#D", parm);
+	  inform (input_location, "redeclared here as %q#D", parm);
 	  return false;
 	}
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-34314.C b/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
index ee0ed01b8d3..b37cac53223 100644
--- a/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
+++ b/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
@@ -4,7 +4,7 @@ template<typename Fun, typename... Args> // { dg-error "template parameter" }
 struct call;
 
 template<typename Fun, typename Arg0>
-struct call // { dg-error "redeclared here" }
+struct call // { dg-message "note: redeclared here" }
 {
     template<typename Sig>
     struct result;
@@ -21,7 +21,7 @@ template<typename Fun, int... N> // { dg-error "template parameter" }
 struct call2;
 
 template<typename Fun, int N>
-struct call2 // { dg-error "redeclared here" }
+struct call2 // { dg-message "note: redeclared here" }
 {
     template<typename Sig>
     struct result;
@@ -37,7 +37,7 @@ template<typename Fun, template<typename> class... TT> // { dg-error "template p
 struct call3;
 
 template<typename Fun, template<typename> class TT>
-struct call3 // { dg-error "redeclared here" }
+struct call3 // { dg-message "note: redeclared here" }
 {
     template<typename Sig>
     struct result;
diff --git a/gcc/testsuite/g++.dg/template/pr59930-2.C b/gcc/testsuite/g++.dg/template/pr59930-2.C
index a7e6ea4ea9a..65ec58e23f4 100644
--- a/gcc/testsuite/g++.dg/template/pr59930-2.C
+++ b/gcc/testsuite/g++.dg/template/pr59930-2.C
@@ -6,7 +6,7 @@ namespace N {
     // Injects N::N
     template < T > friend class N;
     // { dg-error "template parameter" "" { target *-*-* } .-1 }
-    // { dg-error "redeclared"  "" { target *-*-* } .-2 }
+    // { dg-message "note: redeclared"  "" { target *-*-* } .-2 }
   };
 }
 
diff --git a/gcc/testsuite/g++.dg/template/pr92440.C b/gcc/testsuite/g++.dg/template/pr92440.C
new file mode 100644
index 00000000000..20db5f10586
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr92440.C
@@ -0,0 +1,10 @@
+// PR c++/92440
+// { dg-do compile }
+
+template <int T> // { dg-error "template parameter" }
+struct S {
+    template <class U>
+    friend struct S;  // { dg-message "note: redeclared here as" }
+};
+
+S<0> s;
diff --git a/gcc/testsuite/g++.dg/template/redecl2.C b/gcc/testsuite/g++.dg/template/redecl2.C
index 4dd432e6fea..31334f4f334 100644
--- a/gcc/testsuite/g++.dg/template/redecl2.C
+++ b/gcc/testsuite/g++.dg/template/redecl2.C
@@ -6,4 +6,4 @@
 // non-type template parameter.
 
 template <int i> struct X;	// { dg-error "template parameter" }
-template <int* p> struct X;	// { dg-error "redeclared here" }
+template <int* p> struct X;	// { dg-message "note: redeclared here" }
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C b/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
index 4a580e17742..48517f5d1d3 100644
--- a/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
+++ b/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
@@ -16,7 +16,7 @@ template <class T> // { dg-error "template parameter" }
 struct S3;
 
 template <int I>
-struct S3; // { dg-error "redeclared here" } 
+struct S3; // { dg-message "note: redeclared here" } 
 
 template <template <class T> class C>
-struct S3; // { dg-error "redeclared here" } 
+struct S3; // { dg-message "note: redeclared here" } 

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