Separate first nonblank line motion

src/session.zig

@@ -31,6 +31,7 @@ pub const Command = union(enum) {
     move_word_forward,
     move_word_back,
     move_word_end,
+    move_line_first_nonblank,
     insert: []const u8,
     insert_pair: Pair,
     delete_backward,
@@ -95,6 +96,7 @@ pub const Buffer = struct {
             .move_word_forward => self.moveWordForward(),
             .move_word_back => self.moveWordBack(),
             .move_word_end => self.moveWordEnd(),
+            .move_line_first_nonblank => self.moveLineFirstNonblank(),
             .insert => |text| try self.insert(text),
             .insert_pair => |pair| try self.insertPair(pair),
             .delete_backward => self.deleteBackward(),
@@ -267,6 +269,14 @@ pub const Buffer = struct {
         self.refreshCellResetPreferred();
     }
 
+    pub fn moveLineFirstNonblank(self: *Buffer) void {
+        const range = self.currentLineRange(false);
+        var at = range.start;
+        while (at < range.end and (self.bytes.items[at] == ' ' or self.bytes.items[at] == '\t')) : (at += 1) {}
+        self.cursor.byte = at;
+        self.refreshCellResetPreferred();
+    }
+
     pub fn moveDocumentStart(self: *Buffer) void {
         self.cursor.byte = 0;
         self.refreshCellResetPreferred();
@@ -795,3 +805,33 @@ test "regular: document motions jump to top and bottom line" {
     try std.testing.expectEqual(@as(usize, 0), snap.cursor_byte);
     try std.testing.expectEqual(@as(usize, 0), snap.cursor_cell);
 }
+
+test "regular: line first-nonblank is distinct from absolute line start" {
+    var buffer = try Buffer.openFromBytes(std.testing.allocator, "top\n  \talpha\nend");
+    defer buffer.deinit();
+
+    buffer.moveDown();
+    buffer.moveLineEnd();
+    try std.testing.expectEqual(@as(usize, 12), buffer.cursor.byte);
+
+    buffer.moveLineStart();
+    try std.testing.expectEqual(@as(usize, 4), buffer.cursor.byte);
+
+    buffer.moveLineEnd();
+    buffer.moveLineFirstNonblank();
+    try std.testing.expectEqual(@as(usize, 7), buffer.cursor.byte);
+    try std.testing.expectEqual(@as(usize, 2), buffer.cursor.cell);
+}
+
+test "adversarial: line first-nonblank on blank or whitespace-only line goes to line end" {
+    var buffer = try Buffer.openFromBytes(std.testing.allocator, "a\n  \n\t\tb");
+    defer buffer.deinit();
+
+    buffer.moveDown();
+    buffer.moveLineFirstNonblank();
+    try std.testing.expectEqual(@as(usize, 4), buffer.cursor.byte);
+
+    buffer.moveDown();
+    buffer.moveLineFirstNonblank();
+    try std.testing.expectEqual(@as(usize, 7), buffer.cursor.byte);
+}