diagnostics: also show suggested %empty

* src/reader.c (grammar_rule_check_and_complete): Suggest to add %empty.
* tests/actions.at, tests/diagnostics.at: Adjust expectations.

NEWS

@@ -39,6 +39,27 @@ GNU Bison NEWS
   The gain is typically moderate, but in extreme cases (very simple user
   actions), a 10% improvement can be observed.
 
+*** Diagnostics with insertion
+
+  The diagnostics now display suggestion below the underlined source.
+  Replacement for undeclared symbols are now also suggested.
+
+    $ cat /tmp/foo.y
+    %%
+    list: lis '.' |
+
+    $ bison -Wall foo.y
+    foo.y:2.7-9: error: symbol 'lis' is used, but is not defined as a token and has no rules; did you mean 'list'?
+        2 | list: lis '.' |
+          |       ^~~
+          |       list
+    foo.y:2.16: warning: empty rule without %empty [-Wempty-rule]
+        2 | list: lis '.' |
+          |                ^
+          |                %empty
+    foo.y: warning: fix-its can be applied.  Rerun with option '--update'. [-Wother]
+
+
 *** Debug traces in Java
 
   The Java backend no longer emits code and data for parser tracing if the

src/reader.c

@@ -358,6 +358,8 @@ grammar_rule_check_and_complete (symbol_list *r)
       && warning_is_enabled (Wempty_rule))
     {
       complain (&r->rhs_loc, Wempty_rule, _("empty rule without %%empty"));
+      if (feature_flag & feature_caret)
+        location_caret_suggestion (r->rhs_loc, "%empty", stderr);
       location loc = r->rhs_loc;
       loc.end = loc.start;
       fixits_register (&loc, " %empty ");

tests/actions.at

@@ -134,6 +134,7 @@ AT_BISON_CHECK([-fcaret -Wempty-rule 1.y], [0], [],
 [[1.y:11.17-18: warning: empty rule without %empty [-Wempty-rule]
    11 | a: /* empty. */ {};
       |                 ^~
+      |                 %empty
 1.y: warning: fix-its can be applied.  Rerun with option '--update'. [-Wother]
 ]])
 
@@ -149,9 +150,11 @@ AT_BISON_CHECK([-fcaret 2.y], [0], [],
 [[2.y:11.17-18: warning: empty rule without %empty [-Wempty-rule]
    11 | a: /* empty. */ {};
       |                 ^~
+      |                 %empty
 2.y:13.17-18: warning: empty rule without %empty [-Wempty-rule]
    13 | c: /* empty. */ {};
       |                 ^~
+      |                 %empty
 2.y: warning: fix-its can be applied.  Rerun with option '--update'. [-Wother]
 ]])
 

tests/diagnostics.at

@@ -128,18 +128,23 @@ e:
 [[input.y:11.4-5: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    11 | a: <warning>{}</warning>
       |    <warning>^~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:12.3-13.1: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    12 | b:<warning>{</warning>
       |   <warning>^</warning>
+      |   <fixit-insert>%empty</fixit-insert>
 input.y:14.3: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    14 | c:
       |   <warning>^</warning>
+      |   <fixit-insert>%empty</fixit-insert>
 input.y:16.2: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    16 | :
       |  <warning>^</warning>
+      |  <fixit-insert>%empty</fixit-insert>
 input.y:17.3: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    17 | e:
       |   <warning>^</warning>
+      |   <fixit-insert>%empty</fixit-insert>
 input.y: <warning>warning:</warning> fix-its can be applied.  Rerun with option '--update'. [<warning>-Wother</warning>]
 ]])
 
@@ -167,27 +172,35 @@ h: {	🐃	}
 [[input.y:11.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    11 | a: <warning>{		}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:12.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    12 | b: <warning>{            }</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:13.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    13 | c: <warning>{------------}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:14.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    14 | d: <warning>{éééééééééééé}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:15.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    15 | e: <warning>{∇⃗×𝐸⃗ = -∂𝐵⃗/∂t}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:16.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    16 | f: <warning>{	42	}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:17.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    17 | g: <warning>{	"฿¥$€₦"	}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y:18.4-17: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    18 | h: <warning>{	🐃	}</warning>
       |    <warning>^~~~~~~~~~~~~~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 input.y: <warning>warning:</warning> fix-its can be applied.  Rerun with option '--update'. [<warning>-Wother</warning>]
 ]])
 
@@ -211,7 +224,9 @@ b: {}
 [[input.y:11.4-5: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
    11 | a: <warning>{}</warning>
       |    <warning>^~</warning>
+      |    <fixit-insert>%empty</fixit-insert>
 /dev/stdout:1.4-5: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
+      |    <fixit-insert>%empty</fixit-insert>
 /dev/stdout: <warning>warning:</warning> fix-its can be applied.  Rerun with option '--update'. [<warning>-Wother</warning>]
 ]])
 
@@ -307,6 +322,7 @@ input.y:10.9-11:     previous declaration
  <note>FOO</note>
       |         <note>^~~</note>
 input.y:13.5: <warning>warning:</warning> empty rule without %empty [<warning>-Wempty-rule</warning>]
+   13 | exp:
       |     <warning>^</warning>
       |     <fixit-insert>%empty</fixit-insert>
 input.y: <warning>warning:</warning> fix-its can be applied.  Rerun with option '--update'. [<warning>-Wother</warning>]