symbol: use the first occurrence as an LHS as defining location

Currently on the following grammar: %type <foo> foo %% start: foo | bar | "baz" foo: foo bar: bar bison reports: warning: 2 nonterminals useless in grammar [-Wother] warning: 4 rules useless in grammar [-Wother] 1.13-15: warning: nonterminal useless in grammar: foo [-Wother] %type <foo> foo ^^^ 3.14-16: warning: nonterminal useless in grammar: bar [-Wother] start: foo | bar | "baz" ^^^ [...] i.e., the location of the first occurrence of a symbol is taken as its definition point. In the case of nonterminals, the first occurrence as a left-hand side of a rule makes more sense: warning: 2 nonterminals useless in grammar [-Wother] warning: 4 rules useless in grammar [-Wother] 4.1-3: warning: nonterminal useless in grammar: foo [-Wother] foo: foo ^^^ 5.1-3: warning: nonterminal useless in grammar: bar [-Wother] bar: bar ^^^ [...] * src/symtab.h, src/symtab.c (symbol::location_of_lhs): New. (symbol_location_as_lhs_set): New. * src/parse-gram.y (current_lhs): Use it. * tests/reduce.at: Update locations.
2026-03-09 12:23:04 +00:00 · 2015-01-14 13:41:32 +01:00
parent 650af77812
commit 875ef1b90c
7 changed files with 46 additions and 17 deletions
--- a/9
+++ b/9
@@ -33,13 +33,14 @@ GNU Bison NEWS
                                      ^^^^^^^^^^^

  Now, rules whose left-hand side symbol is useless are no longer reported
-  as useless.
+  as useless.  The locations of the errors have also been adjusted to point
+  to the first use of the nonterminal as a left-hand side of a rule:

    warning: 1 nonterminal useless in grammar [-Wother]
    warning: 4 rules useless in grammar [-Wother]
-    2.14-16: warning: nonterminal useless in grammar: exp [-Wother]
-     input: '0' | exp
-                  ^^^
+    3.1-3: warning: nonterminal useless in grammar: exp [-Wother]
+     exp: exp '+' exp | exp '-' exp | '(' exp ')'
+     ^^^
    2.14-16: warning: rule useless in grammar [-Wother]
     input: '0' | exp
                  ^^^
--- a/src/parse-gram.c
+++ b/src/parse-gram.c
@@ -1,4 +1,4 @@
-/* A Bison parser, made by GNU Bison 3.0.2.13-975bb-dirty.  */
+/* A Bison parser, made by GNU Bison 3.0.2.29-9a91e.  */

 /* Bison implementation for Yacc-like parsers in C

@@ -44,7 +44,7 @@
 #define YYBISON 1

 /* Bison version.  */
-#define YYBISON_VERSION "3.0.2.13-975bb-dirty"
+#define YYBISON_VERSION "3.0.2.29-9a91e"

 /* Skeleton name.  */
 #define YYSKELETON_NAME "yacc.c"
@@ -3118,6 +3118,8 @@ current_lhs (symbol *sym, location loc, named_ref *ref)
 {
  current_lhs_symbol = sym;
  current_lhs_location = loc;
+  if (sym)
+    symbol_location_as_lhs_set (sym, loc);
  /* In order to simplify memory management, named references for lhs
     are always assigned by deep copy into the current symbol_list
     node.  This is because a single named-ref in the grammar may
--- a/src/parse-gram.h
+++ b/src/parse-gram.h
@@ -1,4 +1,4 @@
-/* A Bison parser, made by GNU Bison 3.0.2.13-975bb-dirty.  */
+/* A Bison parser, made by GNU Bison 3.0.2.29-9a91e.  */

 /* Bison interface for Yacc-like parsers in C

--- a/src/parse-gram.y
+++ b/src/parse-gram.y
@@ -865,6 +865,8 @@ current_lhs (symbol *sym, location loc, named_ref *ref)
 {
  current_lhs_symbol = sym;
  current_lhs_location = loc;
+  if (sym)
+    symbol_location_as_lhs_set (sym, loc);
  /* In order to simplify memory management, named references for lhs
     are always assigned by deep copy into the current symbol_list
     node.  This is because a single named-ref in the grammar may
--- a/src/symtab.c
+++ b/src/symtab.c
@@ -105,6 +105,7 @@ symbol_new (uniqstr tag, location loc)

  res->tag = tag;
  res->location = loc;
+  res->location_of_lhs = false;
  res->alias = NULL;
  res->content = sym_content_new (res);
  res->is_alias = false;
@@ -189,6 +190,7 @@ code_props_type_string (code_props_type kind)
  assert (0);
 }

+
 /*----------------------------------------.
 | Create a new semantic type, named TAG.  |
 `----------------------------------------*/
@@ -307,6 +309,13 @@ semantic_type_redeclaration (semantic_type *s, const char *what, location first,
 }


+void
+symbol_location_as_lhs_set (symbol *sym, location loc)
+{
+  if (!sym->location_of_lhs)
+    sym->location = loc;
+}
+

 /*-----------------------------------------------------------------.
 | Set the TYPE_NAME associated with SYM.  Does nothing if passed 0 |
--- a/src/symtab.h
+++ b/src/symtab.h
@@ -87,10 +87,19 @@ struct symbol
 {
  /** The key, name of the symbol.  */
  uniqstr tag;
-  /** The location of its first occurrence.  */
+
+  /** The "defining" location.  */
  location location;

-  /* Points to the other in the symbol-string pair for an alias. */
+  /** Whether \a location is about the first uses as left-hand side
+      symbol of a rule (true), or simply the first occurrence (e.g.,
+      in a %type, or as a rhs symbol of a rule).  The former type of
+      location is more natural in error messages.  This Boolean helps
+      moving from location of the first occurrence to first use as
+      lhs. */
+  bool location_of_lhs;
+
+  /** Points to the other in the symbol-string pair for an alias. */
  symbol *alias;

  /** Whether this symbol is the alias of another or not. */
@@ -177,6 +186,12 @@ uniqstr symbol_id_get (symbol const *sym);
 */
 void symbol_make_alias (symbol *sym, symbol *str, location loc);

+/**
+ * This symbol is used as the lhs of a rule.  Record this location
+ * as definition point, if not already done.
+ */
+void symbol_location_as_lhs_set (symbol *sym, location loc);
+
 /** Set the \c type_name associated with \c sym.

    Do nothing if passed 0 as \c type_name.  */
--- a/tests/reduce.at
+++ b/tests/reduce.at
@@ -254,9 +254,9 @@ not-reduced.y: warning: 3 rules useless in grammar [-Wother]
 not-reduced.y:14.1-13: warning: nonterminal useless in grammar: not_reachable [-Wother]
 not_reachable: useful  { /* A not reachable action. */ }
 ^^^^^^^^^^^^^
-not-reduced.y:11.6-19: warning: nonterminal useless in grammar: non_productive [-Wother]
-    | non_productive    { /* A non productive action. */ }
-      ^^^^^^^^^^^^^^
+not-reduced.y:17.1-14: warning: nonterminal useless in grammar: non_productive [-Wother]
+ non_productive: non_productive useless_token
+ ^^^^^^^^^^^^^^
 not-reduced.y:11.6-57: warning: rule useless in grammar [-Wother]
    | non_productive    { /* A non productive action. */ }
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -330,12 +330,12 @@ indirection: underivable;
 AT_BISON_CHECK([[-fcaret input.y]], 0, [],
 [[input.y: warning: 2 nonterminals useless in grammar [-Wother]
 input.y: warning: 3 rules useless in grammar [-Wother]
-input.y:5.15-25: warning: nonterminal useless in grammar: underivable [-Wother]
- exp: useful | underivable;
-               ^^^^^^^^^^^
-input.y:6.14-24: warning: nonterminal useless in grammar: indirection [-Wother]
+input.y:6.1-11: warning: nonterminal useless in grammar: underivable [-Wother]
 underivable: indirection;
-              ^^^^^^^^^^^
+ ^^^^^^^^^^^
+input.y:7.1-11: warning: nonterminal useless in grammar: indirection [-Wother]
+ indirection: underivable;
+ ^^^^^^^^^^^
 input.y:5.15-25: warning: rule useless in grammar [-Wother]
 exp: useful | underivable;
               ^^^^^^^^^^^