feat: Add auto-indent on Enter

README.md

@@ -53,6 +53,9 @@ If no file is given, the editor opens an empty, unnamed buffer.
 | Backspace / Delete                   | Delete a character or the selection              |
 | Esc                                  | Clear the selection                              |
 
+Enter also auto-indents: a new line inherits the current line's leading
+whitespace.
+
 ## License
 
 GNU GPL 3.0.

src/editor.c

@@ -497,10 +497,24 @@ void editor_insert_newline(editor_t *ed)
     if (editor_has_selection(ed)) {
         delete_selection(ed);
     }
+
+    /* Auto-indent: carry the current line's leading whitespace over to the
+     * new line, unless the cursor is still inside that whitespace (the
+     * split already carries it over correctly in that case). */
+    size_t indent_len = first_non_blank(&ed->buf.lines[ed->cy]);
+    if (ed->cx < indent_len) {
+        indent_len = 0;
+    }
+
     buffer_split_line(&ed->buf, ed->cy, ed->cx);
     ed->cy += 1;
     ed->cx = 0;
-    ed->goal_rx = 0;
+
+    if (indent_len > 0) {
+        buffer_insert_bytes(&ed->buf, ed->cy, 0, ed->buf.lines[ed->cy - 1].chars, indent_len);
+        ed->cx = indent_len;
+    }
+    ed->goal_rx = editor_cx_to_rx(&ed->buf.lines[ed->cy], ed->cx);
 
     commit_edit(ed, &cap, ed->cy, ed->cx);
 }

tests/meson.build

@@ -1,4 +1,4 @@
-test_names = ['buffer', 'search', 'encoding', 'filetype', 'editor', 'undo', 'clipboard', 'replace']
+test_names = ['buffer', 'search', 'encoding', 'filetype', 'editor', 'undo', 'clipboard', 'replace', 'autoindent']
 
 foreach name : test_names
   test_exe = executable(

tests/test_autoindent.c

@@ -0,0 +1,98 @@
+/* SPDX-FileCopyrightText: AnmiTaliDev <anmitalidev@nuros.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include "editor.h"
+
+static void set_line(editor_t *ed, size_t row, const char *text)
+{
+    buffer_insert_bytes(&ed->buf, row, 0, text, strlen(text));
+}
+
+static void test_indent_carried_from_end_of_line(void)
+{
+    editor_t ed;
+    editor_init(&ed, 24, 80);
+    set_line(&ed, 0, "    foo();");
+    ed.cy = 0;
+    ed.cx = ed.buf.lines[0].len;
+
+    editor_insert_newline(&ed);
+
+    assert(ed.buf.num_lines == 2);
+    assert(memcmp(ed.buf.lines[0].chars, "    foo();", 10) == 0);
+    assert(ed.buf.lines[1].len == 4);
+    assert(memcmp(ed.buf.lines[1].chars, "    ", 4) == 0);
+    assert(ed.cy == 1 && ed.cx == 4);
+
+    editor_undo(&ed);
+    assert(ed.buf.num_lines == 1);
+    assert(ed.buf.lines[0].len == 10);
+
+    editor_free(&ed);
+}
+
+static void test_indent_carried_mid_line(void)
+{
+    editor_t ed;
+    editor_init(&ed, 24, 80);
+    set_line(&ed, 0, "  if (x) {y}");
+    ed.cy = 0;
+    ed.cx = 9; /* right after "  if (x) " (before '{') */
+
+    editor_insert_newline(&ed);
+
+    assert(ed.buf.num_lines == 2);
+    assert(memcmp(ed.buf.lines[0].chars, "  if (x) ", 9) == 0);
+    assert(memcmp(ed.buf.lines[1].chars, "  {y}", 5) == 0);
+    assert(ed.cx == 2);
+
+    editor_free(&ed);
+}
+
+static void test_no_indent_duplicated_when_splitting_inside_whitespace(void)
+{
+    editor_t ed;
+    editor_init(&ed, 24, 80);
+    set_line(&ed, 0, "    x");
+    ed.cy = 0;
+    ed.cx = 2; /* inside the leading whitespace */
+
+    editor_insert_newline(&ed);
+
+    assert(ed.buf.num_lines == 2);
+    assert(memcmp(ed.buf.lines[0].chars, "  ", 2) == 0);
+    assert(ed.buf.lines[1].len == 3);
+    assert(memcmp(ed.buf.lines[1].chars, "  x", 3) == 0);
+
+    editor_free(&ed);
+}
+
+static void test_no_indent_on_flush_left_line(void)
+{
+    editor_t ed;
+    editor_init(&ed, 24, 80);
+    set_line(&ed, 0, "hello");
+    ed.cy = 0;
+    ed.cx = 5;
+
+    editor_insert_newline(&ed);
+
+    assert(ed.buf.num_lines == 2);
+    assert(ed.buf.lines[1].len == 0);
+    assert(ed.cx == 0);
+
+    editor_free(&ed);
+}
+
+int main(void)
+{
+    test_indent_carried_from_end_of_line();
+    test_indent_carried_mid_line();
+    test_no_indent_duplicated_when_splitting_inside_whitespace();
+    test_no_indent_on_flush_left_line();
+    return 0;
+}