When a literal string is used to define two different tokens,

`bison -v' segfaults.
Reported by Piotr Gackiewicz, and fixed by Neil Booth.
* tests/regression.m4: New file.
Include the core of the sample provided by Piotr Gackiewicz.
* src/reader.c (parse_token_decl): Diagnose bad cases, and proceed
properly.

tests/Makefile.am

@@ -21,7 +21,7 @@
 # Distribute the testsuite since GNU M4 is needed to build it.
 noinst_SCRIPTS = testsuite
 
-SUITE = calc.m4
+SUITE = calc.m4 regression.m4
 
 EXTRA_DIST = atgeneral.m4 suite.m4 $(SUITE)
 

tests/regression.m4

@@ -0,0 +1,26 @@
+#                                                        -*- Autoconf -*-
+
+cat <<EOF
+
+Regression tests.
+
+EOF
+
+AT_SETUP(Duplicate string)
+
+AT_DATA([duplicate.y],
+[[/* `Bison -v' used to dump core when two tokens are defined with the same
+   string, as LE and GE below. */
+
+%token NUM
+%token LE "<="
+%token GE "<="
+
+%%
+exp: '(' exp ')' | NUM ;
+%%
+]])
+
+AT_CHECK([bison -v duplicate.y -o duplicate.c], 0, ignore, ignore)
+
+AT_CLEANUP(duplicate.*)

tests/suite.m4

@@ -5,3 +5,4 @@
 AT_INIT([bison])
 
 AT_INCLUDE([calc.m4])
+AT_INCLUDE([regression.m4])