From 3abad26a2d0c063719745156dc2d40681c5f969d Mon Sep 17 00:00:00 2001
From: Akim Demaille <akim.demaille@gmail.com>
Date: Thu, 31 Dec 2020 07:55:05 +0100
Subject: [PATCH] %merge: associate it to its first definition, not the latest

Currently each time we meet %merge we record this location as the
defining location (and symbol).  Instead, record the first definition.

In the generated code we go from

    yy0->A = merge (*yy0, *yy1);

to

    yy0->S = merge (*yy0, *yy1);

where S was indeed the first symbol, and in the diagnostics we go from

    glr-regr18.y:30.18-24: error: result type clash on merge function 'merge': <type2> != <type1>
       30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~
    glr-regr18.y:29.18-24: note: previous declaration
       29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~
    glr-regr18.y:31.13-19: error: result type clash on merge function 'merge': <type3> != <type2>
       31 | sym3: %merge<merge> { $$ = 0; } ;
          |             ^~~~~~~
    glr-regr18.y:30.18-24: note: previous declaration
       30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~

to

    glr-regr18.y:30.18-24: error: result type clash on merge function 'merge': <type2> != <type1>
       30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~
    glr-regr18.y:29.18-24: note: previous declaration
       29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~
    glr-regr18.y:31.13-19: error: result type clash on merge function 'merge': <type3> != <type1>
       31 | sym3: %merge<merge> { $$ = 0; } ;
          |             ^~~~~~~
    glr-regr18.y:29.18-24: note: previous declaration
       29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
          |                  ^~~~~~~

where both duplicates are reported against definition 1, rather than
using definition 1 as a reference when diagnosing about definition 2,
and then 2 as a reference for 3.

* src/reader.c (record_merge_function_type): Keep the first definition.
* tests/glr-regression.at: Adjust.
---
 src/reader.c            | 27 ++++++++++++++++-----------
 tests/glr-regression.at |  6 +++---
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/src/reader.c b/src/reader.c
index b71dd916..a43c5e41 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -122,19 +122,24 @@ record_merge_function_type (int merger, symbol *sym, location declaration_loc)
        merge_function = merge_function->next)
     merger_find += 1;
   aver (merge_function != NULL && merger_find == merger);
-  if (merge_function->sym && merge_function->sym->content->type_name
-      && !UNIQSTR_EQ (merge_function->sym->content->type_name, type))
+  if (merge_function->sym && merge_function->sym->content->type_name)
     {
-      complain (&declaration_loc, complaint,
-                _("result type clash on merge function %s: "
-                "<%s> != <%s>"),
-                quote (merge_function->name), type,
-                merge_function->sym->content->type_name);
-      subcomplain (&merge_function->type_declaration_loc, complaint,
-                   _("previous declaration"));
+      if (!UNIQSTR_EQ (merge_function->sym->content->type_name, type))
+        {
+          complain (&declaration_loc, complaint,
+                    _("result type clash on merge function %s: "
+                      "<%s> != <%s>"),
+                    quote (merge_function->name), type,
+                    merge_function->sym->content->type_name);
+          subcomplain (&merge_function->type_declaration_loc, complaint,
+                       _("previous declaration"));
+        }
+    }
+  else
+    {
+      merge_function->sym = sym;
+      merge_function->type_declaration_loc = declaration_loc;
     }
-  merge_function->sym = sym;
-  merge_function->type_declaration_loc = declaration_loc;
 }
 
 /*--------------------------------------.
diff --git a/tests/glr-regression.at b/tests/glr-regression.at
index a6deb9c9..51c6ee5e 100644
--- a/tests/glr-regression.at
+++ b/tests/glr-regression.at
@@ -1682,11 +1682,11 @@ AT_BISON_CHECK([[-o glr-regr18.c -rall -fcaret glr-regr18.y]], 1, [],
 glr-regr18.y:27.18-24: note: previous declaration
    27 | sym1: sym2 %merge<merge> { $$ = $][1; } ;
       |                  ^~~~~~~
-glr-regr18.y:29.13-19: error: result type clash on merge function 'merge': <type3> != <type2>
+glr-regr18.y:29.13-19: error: result type clash on merge function 'merge': <type3> != <type1>
    29 | sym3: %merge<merge> { $$ = 0; } ;
       |             ^~~~~~~
-glr-regr18.y:28.18-24: note: previous declaration
-   28 | sym2: sym3 %merge<merge> { $$ = $][1; } ;
+glr-regr18.y:27.18-24: note: previous declaration
+   27 | sym1: sym2 %merge<merge> { $$ = $][1; } ;
       |                  ^~~~~~~
 ]])