Improve error messages for `$' or `@' followed by `.' or `-'.

[Joel E. Denny]

Hi,

Given this test.y:

  %%
  start: .field { $start = $.field; }
  .field: ;

I find the second line of this error message confusing:

  test.y:2.26-32: invalid reference: `$.field'
  test.y:2.8-35:      symbol not found in production: 
  test.y:2.8-13:      possibly meant: $[.field] at $1

I'd prefer this:

  test.y:2.26-32: invalid reference: `$.field'
  test.y:2.27:        syntax error after `$', expecting integer, letter, `_', 
or `['
  test.y:2.8-13:      possibly meant: $[.field] at $1

The following patch, written against branch-2.5, fixes that.  Any 
objections?

>From 9491fad8a45fb419cfb842a539c3e0588be3df94 Mon Sep 17 00:00:00 2001
From: Joel E. Denny <address@hidden>
Date: Sat, 8 Jan 2011 12:52:04 -0500
Subject: [PATCH] Improve error messages for `$' or `@' followed by `.' or `-'.

Previously, for this special case of an invalid reference, the
usual "symbol not found in production:" was printed.  However,
because the symbol name was parsed as the empty string, that
message was followed immediately by a newline instead of a symbol
name.  In reality, this is a syntax error, so the reference is
invalid regardless of the symbols actually appearing in the
production.
* src/scan-code.l (parse_ref): Report the above case as a syntax
error.  Other than that, continue to handle this case like any
other invalid reference that Bison manages to parse because
"possibly meant" messages can still be helpful to the user.
* tests/named-refs.at ($ or @ followed by . or -): New test group.
---
 ChangeLog           |   16 ++++++++++++++++
 src/scan-code.l     |   12 +++++++++++-
 tests/named-refs.at |   29 +++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index a7d8a76..3eaa83d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2011-01-08  Joel E. Denny  <address@hidden>
+
+       Improve error messages for `$' or `@' followed by `.' or `-'.
+       Previously, for this special case of an invalid reference, the
+       usual "symbol not found in production:" was printed.  However,
+       because the symbol name was parsed as the empty string, that
+       message was followed immediately by a newline instead of a symbol
+       name.  In reality, this is a syntax error, so the reference is
+       invalid regardless of the symbols actually appearing in the
+       production.
+       * src/scan-code.l (parse_ref): Report the above case as a syntax
+       error.  Other than that, continue to handle this case like any
+       other invalid reference that Bison manages to parse because
+       "possibly meant" messages can still be helpful to the user.
+       * tests/named-refs.at ($ or @ followed by . or -): New test group.
+
 2011-01-05  Alex Rozenman  <address@hidden>
 
        Do not allow identifiers that start with a negative number.
diff --git a/src/scan-code.l b/src/scan-code.l
index e3e6b65..bfe3f66 100644
--- a/src/scan-code.l
+++ b/src/scan-code.l
@@ -620,7 +620,17 @@ parse_ref (char *cp, symbol_list *rule, int rule_length,
         complain_at_indent (text_loc, &indent, _("invalid reference: %s"),
                             quote (text));
         indent += SUB_INDENT;
-        if (midrule_rhs_index)
+        if (len == 0)
+          {
+            location sym_loc = text_loc;
+            sym_loc.start.column += 1;
+            sym_loc.end = sym_loc.start;
+            const char *format =
+              _("syntax error after `%c', expecting integer, letter,"
+                " `_', or `['");
+            complain_at_indent (sym_loc, &indent, format, dollar_or_at);
+          }
+        else if (midrule_rhs_index)
           {
             const char *format =
               _("symbol not found in production before $%d: %.*s");
diff --git a/tests/named-refs.at b/tests/named-refs.at
index 25af97d..b3b4f5b 100644
--- a/tests/named-refs.at
+++ b/tests/named-refs.at
@@ -561,3 +561,32 @@ test.y:57.8-17: invalid reference: `$<aa>[sym]'
 test.y:54.1-57.21:  symbol not found in production: sym
 ]])
 AT_CLEANUP
+
+#######################################################################
+
+AT_SETUP([[$ or @ followed by . or -]])
+AT_DATA([[test.y]],
+[[
+%%
+start:
+  .field { $.field; }
+| -field { @-field; }
+| 'a'    { @.field; }
+| 'a'    { $-field; }
+;
+.field: ;
+-field: ;
+]])
+AT_BISON_CHECK([[test.y]], [[1]], [],
+[[test.y:4.12-18: invalid reference: `$.field'
+test.y:4.13:        syntax error after `$', expecting integer, letter, `_', or 
`@<:@'
+test.y:4.3-8:       possibly meant: $[.field] at $1
+test.y:5.12-18: invalid reference: address@hidden'
+test.y:5.13:        syntax error after `@', expecting integer, letter, `_', or 
`@<:@'
+test.y:5.3-8:       possibly meant: @[-field] at $1
+test.y:6.12-18: invalid reference: address@hidden'
+test.y:6.13:        syntax error after `@', expecting integer, letter, `_', or 
`@<:@'
+test.y:7.12-18: invalid reference: `$-field'
+test.y:7.13:        syntax error after `$', expecting integer, letter, `_', or 
`@<:@'
+]])
+AT_CLEANUP
-- 
1.7.0.4