doc: introduce %empty and -Wempty-rule

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 5b9a6e803a81838b73fc9793eb057773fee10caa..564b087ec146b638741742cd0e457c80df72c32c 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -58,6 +58,29 @@ GNU Bison NEWS
   activated by default.  The old format can still be used by invoking Bison
   with -fno-caret (or -fnone).
 
   activated by default.  The old format can still be used by invoking Bison
   with -fno-caret (or -fnone).
 

+  Some error messages that reproduced excerpts of the grammar are now using
+  the caret information only.  For instance on:
+
+    %%
+    exp: 'a' | 'a';
+
+  Bison 2.7 reports:
+
+    in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+    in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
+
+  Now bison reports:
+
+    in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+    in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
+     exp: 'a' | 'a';
+                ^^^
+
+  and "bison -fno-caret" reports:
+
+    in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+    in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
+

 *** Enhancements of the -Werror option
 
   The -Werror=CATEGORY option is now recognized, and will treat specified
 *** Enhancements of the -Werror option
 
   The -Werror=CATEGORY option is now recognized, and will treat specified


@@ -339,6 +362,28 @@ GNU Bison NEWS
      %nonassoc '='
                ^^^
 
      %nonassoc '='
                ^^^
 

+** Empty rules
+
+  Empty rules (i.e., with an empty right-hand side) can now be explicitly
+  marked by the new %empty directive.  Using %empty on a non-empty rule is
+  an error.  The new -Wempty-rule warning reports empty rules without
+  %empty.  On the following grammar:
+
+    %%
+    s: a b c;
+    a: ;
+    b: %empty;
+    c: 'a' %empty;
+
+  bison reports:
+
+    3.4-5: warning: empty rule without %empty [-Wempty-rule]
+     a: {}
+        ^^
+    5.8-13: error: %empty on non-empty rule
+     c: 'a' %empty {};
+            ^^^^^^
+

 ** Java skeleton improvements
 
   Contributed by Paolo Bonzini.
 ** Java skeleton improvements
 
   Contributed by Paolo Bonzini.