screen: show an embedded newline in filenames as ^J instead of ^@

The byte 0x0A means 0x00 *only* when it is found in nano's internal
representation of a file's data, not when it occurs in a file name.

This fixes the second part of https://savannah.gnu.org/bugs/?49867.

src/chars.c

@@ -225,10 +225,7 @@ bool is_word_mbchar(const char *c, bool allow_punct)
 /* Return the visible representation of control character c. */
 char control_rep(const signed char c)
 {
-    /* An embedded newline is an encoded null. */
-    if (c == '\n')
-	return '@';
-    else if (c == DEL_CODE)
+    if (c == DEL_CODE)
 	return '?';
     else if (c == -97)
 	return '=';
@@ -239,8 +236,12 @@ char control_rep(const signed char c)
 }
 
 /* Return the visible representation of multibyte control character c. */
-char control_mbrep(const char *c)
+char control_mbrep(const char *c, bool isdata)
 {
+    /* An embedded newline is an encoded null *if* it is data. */
+    if (*c == '\n' && isdata)
+	return '@';
+
 #ifdef ENABLE_UTF8
     if (use_utf8) {
 	if ((unsigned char)c[0] < 128)

src/proto.h

@@ -207,7 +207,7 @@ bool is_cntrl_mbchar(const char *c);
 bool is_punct_mbchar(const char *c);
 bool is_word_mbchar(const char *c, bool allow_punct);
 char control_rep(const signed char c);
-char control_mbrep(const char *c);
+char control_mbrep(const char *c, bool isdata);
 int length_of_char(const char *c, int *width);
 int mbwidth(const char *c);
 int mb_cur_max(void);

src/winio.c

@@ -1803,11 +1803,11 @@ void check_statusblank(void)
  * caller wants to display buf starting with column start_col, and
  * extending for at most span columns.  start_col is zero-based.  span
  * is one-based, so span == 0 means you get "" returned.  The returned
- * string is dynamically allocated, and should be freed.  If dollars is
+ * string is dynamically allocated, and should be freed.  If isdata is
  * TRUE, the caller might put "$" at the beginning or end of the line if
  * it's too long. */
 char *display_string(const char *buf, size_t start_col, size_t span,
-	bool dollars)
+	bool isdata)
 {
     size_t start_index;
 	/* Index in buf of the first character shown. */
@@ -1818,9 +1818,8 @@ char *display_string(const char *buf, size_t start_col, size_t span,
     size_t index;
 	/* Current position in converted. */
 
-    /* If dollars is TRUE, make room for the "$" at the end of the
-     * line. */
-    if (dollars && span > 0 && strlenpt(buf) > start_col + span)
+    /* If this is data, make room for the "$" at the end of the line. */
+    if (isdata && !ISSET(SOFTWRAP) && strlenpt(buf) > start_col + span)
 	span--;
 
     if (span == 0)
@@ -1841,12 +1840,12 @@ char *display_string(const char *buf, size_t start_col, size_t span,
     buf += start_index;
 
     if (*buf != '\0' && *buf != '\t' &&
-	(column < start_col || (dollars && column > 0))) {
+	(column < start_col || (isdata && column > 0))) {
 	/* We don't display the complete first character as it starts to
 	 * the left of the screen. */
 	if (is_cntrl_mbchar(buf)) {
 	    if (column < start_col) {
-		converted[index++] = control_mbrep(buf);
+		converted[index++] = control_mbrep(buf, isdata);
 		start_col++;
 		buf += parse_mbchar(buf, NULL, NULL);
 	    }
@@ -1909,7 +1908,7 @@ char *display_string(const char *buf, size_t start_col, size_t span,
 	/* If buf contains a control character, represent it. */
 	if (is_cntrl_mbchar(buf)) {
 	    converted[index++] = '^';
-	    converted[index++] = control_mbrep(buf);
+	    converted[index++] = control_mbrep(buf, isdata);
 	    start_col += 2;
 	    buf += charlength;
 	    continue;
@@ -2743,15 +2742,11 @@ int update_line(filestruct *fileptr, size_t index)
 
     /* Expand the line, replacing tabs with spaces, and control
      * characters with their displayed forms. */
-#ifdef NANO_TINY
     converted = display_string(fileptr->data, page_start, editwincols, TRUE);
-#else
-    converted = display_string(fileptr->data, page_start, editwincols, !ISSET(SOFTWRAP));
 #ifdef DEBUG
     if (ISSET(SOFTWRAP) && strlen(converted) >= editwincols - 2)
 	fprintf(stderr, "update_line(): converted(1) line = %s\n", converted);
 #endif
-#endif /* !NANO_TINY */
 
     /* Paint the line. */
     edit_draw(fileptr, converted, line, page_start);
@@ -2776,7 +2771,7 @@ int update_line(filestruct *fileptr, size_t index)
 
 	    /* Expand the line, replacing tabs with spaces, and control
 	     * characters with their displayed forms. */
-	    converted = display_string(fileptr->data, index, editwincols, !ISSET(SOFTWRAP));
+	    converted = display_string(fileptr->data, index, editwincols, TRUE);
 #ifdef DEBUG
 	    if (ISSET(SOFTWRAP) && strlen(converted) >= editwincols - 2)
 		fprintf(stderr, "update_line(): converted(2) line = %s\n", converted);