From e7eede3273394f3479bb63f92e57780dfc8f2e3d Mon Sep 17 00:00:00 2001
From: Thomas White <taw@bitwiz.org.uk>
Date: Thu, 2 Mar 2017 22:40:58 +0100
Subject: sc_block_delete() may change the top block

---
 src/frame.c            |  4 +++-
 src/narrative_window.c |  2 +-
 src/sc_editor.c        |  2 +-
 src/sc_parse.c         | 27 ++++++++++++++++++++-------
 src/sc_parse.h         |  4 ++--
 5 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/src/frame.c b/src/frame.c
index 36a7983..5a7da8e 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -1021,7 +1021,9 @@ void merge_paragraphs(struct frame *fr, int para)
 
 		const char *c = sc_block_contents(n);
 		if ( strlen(c) == 1 ) {
-			sc_block_delete(scblock, n);
+			SCBlock *ss = scblock;
+			sc_block_delete(&scblock, n);
+			assert(ss == scblock);
 		} else {
 			scblock_delete_text(n, 0, 1);
 		}
diff --git a/src/narrative_window.c b/src/narrative_window.c
index ec5d956..d53002a 100644
--- a/src/narrative_window.c
+++ b/src/narrative_window.c
@@ -153,7 +153,7 @@ static void delete_slide_sig(GSimpleAction *action, GVariant *parameter,
 		return;
 	}
 
-	sc_block_delete(nw->p->scblocks, ns);
+	sc_block_delete(&nw->p->scblocks, ns);
 
 	/* Full rerender */
 	sc_editor_set_scblock(nw->sceditor,
diff --git a/src/sc_editor.c b/src/sc_editor.c
index 38b245d..cf6c594 100644
--- a/src/sc_editor.c
+++ b/src/sc_editor.c
@@ -397,7 +397,7 @@ void sc_editor_redraw(SCEditor *e)
 
 void sc_editor_delete_selected_frame(SCEditor *e)
 {
-	sc_block_delete(e->scblocks, e->selection->scblocks);
+	sc_block_delete(&e->scblocks, e->selection->scblocks);
 	full_rerender(e);
 	emit_change_sig(e);
 }
diff --git a/src/sc_parse.c b/src/sc_parse.c
index ccc6f6a..a497334 100644
--- a/src/sc_parse.c
+++ b/src/sc_parse.c
@@ -213,23 +213,34 @@ static SCBlock *sc_find_parent(SCBlock *top, SCBlock *find)
 
 void sc_block_substitute(SCBlock **top, SCBlock *old, SCBlock *new)
 {
+	if ( old == NULL ) {
+		fprintf(stderr, "Substituting nothing!\n");
+		return;
+	}
+
 	if ( old == *top ) {
 		/* It is the first block */
 		new->next = old->next;
 		*top = new;
 	} else {
-		sc_block_unlink(*top, old);
-		sc_block_append_p(new, *top);
+		sc_block_unlink(top, old);
+		sc_block_append_p(*top, new);
 	}
 }
 
 
-/* Delete "deleteme", which is somewhere under "top" */
-void sc_block_unlink(SCBlock *top, SCBlock *deleteme)
+/* Unlink "deleteme", which is somewhere under "top" */
+void sc_block_unlink(SCBlock **top, SCBlock *deleteme)
 {
-	SCBlock *parent = sc_find_parent(top, deleteme);
+	SCBlock *parent = sc_find_parent(*top, deleteme);
 	if ( parent == NULL ) {
-		fprintf(stderr, "Couldn't find block parent!\n");
+		/* Maybe it's the first block? */
+		if ( *top == deleteme ) {
+			fprintf(stderr, "Unlinking at top\n");
+			*top = (*top)->next;
+		} else {
+			fprintf(stderr, "Couldn't find block parent!\n");
+		}
 		return;
 	}
 
@@ -243,12 +254,14 @@ void sc_block_unlink(SCBlock *top, SCBlock *deleteme)
 }
 
 
-void sc_block_delete(SCBlock *top, SCBlock *deleteme)
+/* Delete "deleteme", which is somewhere under "top" */
+void sc_block_delete(SCBlock **top, SCBlock *deleteme)
 {
 	sc_block_unlink(top, deleteme);
 	sc_block_free(deleteme);
 }
 
+
 /* Frees "bl" and all its children (but not the blocks following it) */
 void sc_block_free(SCBlock *bl)
 {
diff --git a/src/sc_parse.h b/src/sc_parse.h
index dfa3fab..4775996 100644
--- a/src/sc_parse.h
+++ b/src/sc_parse.h
@@ -59,8 +59,8 @@ extern SCBlock *sc_block_append_inside(SCBlock *parent,
 extern SCBlock *sc_block_insert_after(SCBlock *afterme,
                                       char *name, char *opt, char *contents);
 
-extern void sc_block_delete(SCBlock *top, SCBlock *deleteme);
-extern void sc_block_unlink(SCBlock *top, SCBlock *deleteme);
+extern void sc_block_delete(SCBlock **top, SCBlock *deleteme);
+extern void sc_block_unlink(SCBlock **top, SCBlock *deleteme);
 
 extern SCBlock *find_last_child(SCBlock *bl);
 
-- 
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