nitcc: detect and handle correctly states without shifts nor reduces

Signed-off-by: Jean Privat <[email protected]>

contrib/nitcc/src/lrautomaton.nit

@@ -440,11 +440,9 @@ redef class Generator
 			add "\tredef fun action(parser) do"
 			if s.need_guard then
 				add "\t\tparser.peek_token.action_s{s.number}(parser)"
-			else if s.reduces.length == 1 then
+			else
 				add "\t\treduce_{s.reduces.first.cname}(parser)"
 				#gen_reduce_to_nit(s.reduces.first)
-			else
-				abort
 			end
 			add "\tend"
 
@@ -613,8 +611,11 @@ class LRState
 	# Shifts guarded by tokens
 	var guarded_shift = new HashMap[Token, Set[Item]]
 
-	# Does the state need a guard to perform an action?
-	fun need_guard: Bool do return not shifts.is_empty or reduces.length > 1
+	# Does the state need a guard that look at (or consume) the next token to perform an action?
+	# The only `false` case is a state with a single reduce action, it can be performed without checking the token.
+	# A shift always consume the token.
+	# Empty state with no valid future, must consume the token to produces a syntax error
+	fun need_guard: Bool do return not (shifts.is_empty and reduces.length == 1)
 
 	# Is the state LR0?
 	fun is_lr0: Bool do return reduces.length <= 1 and shifts.is_empty or reduces.is_empty
@@ -650,6 +651,12 @@ class LRState
 				abort
 			end
 		end
+		if shifts.is_empty and reduces.is_empty then
+			print "---"
+			print "Empty state {self} without any reduce or shift"
+			print "The possible past: {prefix} has no valid future"
+		end
+
 		# Token to remove as reduction guard to solve S/R conflicts
 		var removed_reduces = new Array[Token]
 		for t, a in guarded_reduce do

contrib/nitcc/tests/calc1.input

@@ -0,0 +1 @@
+1 + 2 - 3 - 4

contrib/nitcc/tests/calc1.sablecc

@@ -6,6 +6,7 @@ Ignored #10, #32;
 e
 	= e '+' a
 	| e '-' a
+	| a
 	;
 a	=
 	| '(' e ')'

contrib/nitcc/tests/gram_empty.input

@@ -0,0 +1 @@
+x

contrib/nitcc/tests/gram_empty.sablecc

@@ -0,0 +1,3 @@
+Parser
+Ignored #10, #32;
+s = s 'x' ;

contrib/nitcc/tests/gram_empty2.input

@@ -0,0 +1 @@
+y x z

contrib/nitcc/tests/gram_empty2.sablecc

@@ -0,0 +1,4 @@
+Parser
+Ignored #10, #32;
+s = a ;
+a = 'x' s | 'y' s 'z';

contrib/nitcc/tests/sav/calc1.input.res

@@ -0,0 +1,17 @@
+Start
+  e_1
+    e_1
+      e_0
+        e_2
+          a_2
+            n@(1:1-1:2)='1'
+        '+'@(1:3-1:4)
+        a_2
+          n@(1:5-1:6)='2'
+      '-'@(1:7-1:8)
+      a_2
+        n@(1:9-1:10)='3'
+    '-'@(1:11-1:12)
+    a_2
+      n@(1:13-1:14)='4'
+  Eof@(2:1-2:1)=''

contrib/nitcc/tests/sav/calc1.res

@@ -1 +0,0 @@
-Runtime error: Aborted (./lrautomaton.nit:507)

contrib/nitcc/tests/sav/gram_empty.input.res

@@ -0,0 +1,3 @@
+NParserError@(1:1-1:2)='x'
+Nodes[Node]
+  'x'@(1:1-1:2)

contrib/nitcc/tests/sav/gram_empty.res

@@ -0,0 +1 @@
+Empty state 0  without any reduce or shift

contrib/nitcc/tests/sav/gram_empty2.input.res

@@ -0,0 +1,5 @@
+NParserError@(1:5-1:6)='z'
+Nodes[Node]
+  'y'@(1:1-1:2)
+  'x'@(1:3-1:4)
+  'z'@(1:5-1:6)