From 35d743c48140ea96fa56c3f63ee8dd0e032cbb2d Mon Sep 17 00:00:00 2001
From: NeilBrown <neil@brown.name>
Date: Sun, 23 Jun 2019 10:21:14 +1000
Subject: [PATCH] parsergen: allow $$OUT to be satisfied are start-of-line.

If a $$OUT (or $$NEWLINE) production is being reduced at
start-of-line (with no indents), then that is satisfactory,
we don't need NEWLINE etc as look-ahead.

This means that in cases where this is relevant, the computed
lookahead is wrong - we shouldn't have striped it.
I don't think this matters as it only affects conflict warnings,
and I think these will be reported at a higher level if relevant.
If essense, the $$OUT marking is like a precendence marking which
suppresses shift/reduce warnings as it say that decision is being made
on some basis other than look-ahead.

Signed-off-by: NeilBrown <neil@brown.name>
---
 csrc/indent_test.mdc | 19 ++++++++++---------
 csrc/parsergen.mdc   | 10 +++++++---
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/csrc/indent_test.mdc b/csrc/indent_test.mdc
index 88e9391..7e4f956 100644
--- a/csrc/indent_test.mdc
+++ b/csrc/indent_test.mdc
@@ -160,7 +160,7 @@ $*statement
 		| NEWLINE Close
 	Block -> Open Statementlist Close ${ $0 = $<2; }$
 		| Open SimpleStatements } ${ $0 = $<2; }$
-		| : SimpleStatements $$NEWLINE ${ $0 = $<2; }$
+		| : SimpleStatements ${ $0 = $<2; }$
 		| : StatementBlock ${ $0 = $<2; }$
 	StatementBlock -> Statementlist $$OUT ${ $0 = $<1; }$
 
@@ -185,9 +185,9 @@ $*statement
 			$0->expr->right = $<3;
 			}$
 	SSline -> SimpleStatements NEWLINE ${ $0 = $<1; }$
-		| SSline NEWLINE ${ $0 = $<1; }$
 	Statement -> SSline ${ $0 = $<1; }$
-		| IfStatement ${ $0 = $<1; }$
+		| IfStatement $$NEWLINE ${ $0 = $<1; }$
+		| Statement NEWLINE ${ $0 = $<1; }$
 
 	$RIGHT else
 
@@ -197,20 +197,16 @@ $*statement
 				$0->thenpart = $<3;
 				}$
 		| IfHead NEWLINE ${ $0 = $<1; }$
-	IfTail -> else Block ${ $0 = $<2; }$
-		| IfTail NEWLINE ${ $0 = $<1; }$
 
 	IfStatement -> IfHead $$else ${ $0 = $<1; }$
-		| IfHead IfTail ${
+		| IfHead else Block ${
 			$0 = $<1;
-			$0->elsepart = $<2;
+			$0->elsepart = $<3;
 			}$
 		| IfHead else IfStatement ${
 			$0 = $<1;
 			$0->elsepart = $<3;
 			}$
-		| IfStatement NEWLINE ${ $0 = $<1; }$
-
 
 $*expression
 	Expression -> Expression + Term ${
@@ -272,6 +268,7 @@ $*expression
 	all = y;
 	if true {yes=x;} else : no=x
 	if true: yes = no; no = yes;
+	if false: yes=ok; else: no=ok
 
 	if false {
 		print = OK
@@ -309,6 +306,10 @@ $*expression
 	if true:
 	    (yes=no);
 	    (no=yes);
+	if false:
+	    (yes=ok);
+	else:
+	    (no=ok);
 	if false:
 	    (print=OK);
 	else:
diff --git a/csrc/parsergen.mdc b/csrc/parsergen.mdc
index 76fec3a..df73f51 100644
--- a/csrc/parsergen.mdc
+++ b/csrc/parsergen.mdc
@@ -2871,9 +2871,13 @@ checks if a given token is in any of these look-ahead sets.
 		force_reduce:
 			if (states[tos->state].reduce_prod >= 0 &&
 			    states[tos->state].newline_only &&
-			    tk->num != TK_newline && tk->num != TK_eof && tk->num != TK_out) {
-				/* Anything other than newline in an error as this
-				 * production must end at EOL
+			    !(tk->num == TK_newline ||
+			      tk->num == TK_eof ||
+			      tk->num == TK_out ||
+			      (tos->indents == 0 && tos->since_newline == 0))) {
+				/* Anything other than newline or out or eof
+				 * in an error unless we are already at start
+				 * of line, as this production must end at EOL.
 				 */
 			} else if (states[tos->state].reduce_prod >= 0) {
 				void **body;
-- 
2.43.0