implement scroll behavior for reverse index, add conformance

conformance/ansi_ri_top.zig

@@ -1,10 +1,25 @@
-//! Reverse Index (RI) - ESC M at the top of the screen.
+//! Reverse Index (RI) - ESC M
+//! Case: test that if the cursor is at the top, it scrolls down.
 const std = @import("std");
 
 pub fn main() !void {
     const stdout = std.io.getStdOut().writer();
-    try stdout.print("\x1B[H", .{}); // move to top-left
+    try stdout.print("A\nB\n", .{});
-    try stdout.print("\x1B[J", .{}); // clear screen
+
-    try stdout.print("\x1BM", .{});
+    try stdout.print("\x0D", .{}); // CR
-    try stdout.print("D\n", .{});
+    try stdout.print("\x0A", .{}); // LF
+    try stdout.print("\x1B[H", .{}); // Top-left
+    try stdout.print("\x1BM", .{}); // Reverse-Index
+    try stdout.print("D", .{});
+
+    try stdout.print("\x0D", .{}); // CR
+    try stdout.print("\x0A", .{}); // LF
+    try stdout.print("\x1B[H", .{}); // Top-left
+    try stdout.print("\x1BM", .{}); // Reverse-Index
+    try stdout.print("E", .{});
+
+    try stdout.print("\n", .{});
+
+    // const stdin = std.io.getStdIn().reader();
+    // _ = try stdin.readByte();
 }

src/terminal/Terminal.zig

@@ -131,6 +131,7 @@ pub fn appendChar(self: *Terminal, alloc: Allocator, c: u8) !void {
     //log.debug("char: {}", .{c});
     const actions = self.parser.next(c);
     for (actions) |action_opt| {
+        if (action_opt) |action| log.info("action: {}", .{action});
         switch (action_opt orelse continue) {
             .print => |p| try self.print(alloc, p),
             .execute => |code| try self.execute(alloc, code),
@@ -267,7 +268,7 @@ fn escDispatch(
     switch (action.final) {
         // RI - Reverse Index
         'M' => switch (action.intermediates.len) {
-            0 => self.reverseIndex(),
+            0 => try self.reverseIndex(alloc),
             else => {
                 log.warn("invalid reverse index command: {}", .{action});
                 return;
@@ -331,7 +332,10 @@ pub fn selectGraphicRendition(self: *Terminal, aspect: ansi.RenditionAspect) !vo
 }
 
 // TODO: test
-pub fn reverseIndex(self: *Terminal) void {
+pub fn reverseIndex(self: *Terminal, alloc: Allocator) !void {
+    if (self.cursor.y == 0)
+        try self.scrollDown(alloc)
+    else
         self.cursor.y -|= 1;
 }
 
@@ -535,6 +539,34 @@ pub fn scrollUp(self: *Terminal, alloc: Allocator) void {
     self.screen.items.len -= 1;
 }
 
+/// Scroll the text down by one row.
+/// TODO: test
+pub fn scrollDown(self: *Terminal, alloc: Allocator) !void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    // TODO: this is horribly expensive. we need to optimize the screen repr
+
+    // We need space for one more row if we aren't at the max.
+    if (self.screen.capacity < self.rows) {
+        try self.screen.ensureTotalCapacity(alloc, self.screen.items.len + 1);
+    }
+
+    // Add one more item if we aren't at the max
+    if (self.screen.items.len < self.rows) {
+        self.screen.items.len += 1;
+    }
+
+    // Shift everything down
+    var i: usize = self.screen.items.len - 1;
+    while (i > 0) : (i -= 1) {
+        self.screen.items[i] = self.screen.items[i - 1];
+    }
+
+    // Clear this row
+    self.screen.items[0] = .{};
+}
+
 fn getOrPutCell(self: *Terminal, alloc: Allocator, x: usize, y: usize) !*Cell {
     const tracy = trace(@src());
     defer tracy.end();