cgram: fix assertion when substituting at the end of the longest line

Reported by Weitian LI via GitHub.

Contrary to the patch suggested in [1], still allow the cursor to be
placed to the very right of the text in a line since that is the usual
behavior of text editors.

Split the function substitute() into two parts:  one that handles the
curses-specific part of checking whether a substitution is possible at
the current cursor position, and one that performs the actual
substitution.  Only the latter is kept in the code section for the
string manipulation functions, the other is moved to the section for
curses code.  Having all the curses code in one place reduces the places
that call beep().  Previously, as well as now, there is a single beep
per invalid key before, but that was not obvious from the previous code.

[1]: https://github.com/DragonFlyBSD/DragonFlyBSD/commit/18d09f18cf4c

1 files changed, 30 insertions, 39 deletions

diff --git a/cgram/cgram.c b/cgram/cgram.c
index 93ebddd9..04b58cbf 100644
--- a/cgram/cgram.c
+++ b/cgram/cgram.c
@@ -1,4 +1,4 @@
-/* $NetBSD: cgram.c,v 1.13 2021/02/22 17:36:42 rillig Exp $ */
+/* $NetBSD: cgram.c,v 1.14 2021/02/22 19:34:07 rillig Exp $ */
 
 /*-
  * Copyright (c) 2013, 2021 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: cgram.c,v 1.13 2021/02/22 17:36:42 rillig Exp $");
+__RCSID("$NetBSD: cgram.c,v 1.14 2021/02/22 19:34:07 rillig Exp $");
 #endif
 
 #include <assert.h>
@@ -279,40 +279,26 @@ encode(void)
 	}
 }
 
-static bool
-substitute(char ch)
+static void
+substitute(char a, char b)
 {
-	assert(cursor_x >= 0 && cursor_x < extent_x);
-	assert(cursor_y >= 0 && cursor_y < extent_y);
-	if (cursor_x >= cur_max_x()) {
-		beep();
-		return false;
-	}
-
-	char och = char_at_cursor();
-	if (!ch_isalpha(och)) {
-		beep();
-		return false;
-	}
-
-	char loch = ch_tolower(och);
-	char uoch = ch_toupper(och);
-	char lch = ch_tolower(ch);
-	char uch = ch_toupper(ch);
+	char la = ch_tolower(a);
+	char ua = ch_toupper(a);
+	char lb = ch_tolower(b);
+	char ub = ch_toupper(b);
 
 	for (int y = 0; y < (int)lines.num; y++) {
 		for (char *p = lines.v[y].s; *p != '\0'; p++) {
-			if (*p == loch)
-				*p = lch;
-			else if (*p == uoch)
-				*p = uch;
-			else if (*p == lch)
-				*p = loch;
-			else if (*p == uch)
-				*p = uoch;
+			if (*p == la)
+				*p = lb;
+			else if (*p == ua)
+				*p = ub;
+			else if (*p == lb)
+				*p = la;
+			else if (*p == ub)
+				*p = ua;
 		}
 	}
-	return true;
 }
 
 static bool
@@ -457,19 +443,24 @@ go_to_next_word(void)
 		go_right();
 }
 
+static bool
+can_substitute_here(int ch)
+{
+	return isascii(ch) &&
+	    ch_isalpha((char)ch) &&
+	    cursor_x < cur_max_x() &&
+	    ch_isalpha(char_at_cursor());
+}
+
 static void
 handle_char_input(int ch)
 {
-	if (isascii(ch) && ch_isalpha((char)ch)) {
-		if (substitute((char)ch)) {
-			if (cursor_x < cur_max_x())
-				cursor_x++;
-			if (cursor_x == cur_max_x())
-				go_to_next_line();
-		}
-	} else if (ch == char_at_cursor())
+	if (ch == char_at_cursor())
+		go_right();
+	else if (can_substitute_here(ch)) {
+		substitute(char_at_cursor(), (char)ch);
 		go_right();
-	else
+	} else
 		beep();
 }