Fix pasting bug.

build.zig

@@ -196,6 +196,22 @@ pub fn build(b: *std.Build) void {
     settings_tests.root_module.addImport("ghostty-vt", ghostty.module("ghostty-vt"));
     test_step.dependOn(&b.addRunArtifact(settings_tests).step);
 
+    // Paste safety is its own root, and for a sharper reason than the rest:
+    // when it says no it says so silently — the terminal simply does not
+    // receive what you pasted — so the rule that decides has to be checkable
+    // without a display. It reaches libghostty-vt for the encoder and nothing
+    // else; the clipboard round trip around it is GTK's and stays in
+    // `Terminal.zig`.
+    const paste_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/paste.zig"),
+            .target = target,
+            .optimize = optimize,
+        }),
+    });
+    paste_tests.root_module.addImport("ghostty-vt", ghostty.module("ghostty-vt"));
+    test_step.dependOn(&b.addRunArtifact(paste_tests).step);
+
     // The shortcut table is its own root for the same reason: chords are parsed
     // from text, written back out as text, and looked up by a key press, and
     // all three are pure data. It reaches libghostty-vt for the key enum and

src/Terminal.zig

@@ -16,6 +16,7 @@ const gtk = @import("gtk");
 const pango = @import("pango");
 const pangocairo = @import("pangocairo");
 const vt = @import("ghostty-vt");
+const paste_rules = @import("paste.zig");
 
 const keymap = @import("key.zig");
 const theme = @import("theme.zig");
@@ -849,20 +850,45 @@ fn onPasteReady(
 /// Type text into the child as though it had been pasted, bracketing it if
 /// the program asked for that.
 pub fn paste(self: *Terminal, text: []const u8) void {
+    if (text.len == 0) return;
+
     const opts: vt.input.PasteOptions = .fromTerminal(&self.session.term);
 
-    // Refuse pastes containing control characters that would execute on
-    // arrival (a newline in unbracketed mode runs the command immediately).
-    if (!vt.input.isSafePaste(text)) {
+    // Whether this is safe to type into the child turns on bracketing, and
+    // this used to ignore that — which refused nearly every real paste, since a
+    // bracketed program is the normal case and multi-line text is the normal
+    // thing to paste. See `paste.zig` for the rule and its tests.
+    if (paste_rules.isUnsafe(text, opts.bracketed)) {
         std.log.warn("refusing unsafe paste", .{});
         return;
     }
 
-    const parts = vt.input.encodePaste(text, opts) catch |err| {
-        std.log.warn("paste encode failed: {s}", .{@errorName(err)});
+    // Encoding rewrites bytes in place — the control characters xterm turns
+    // into spaces, and newlines into carriage returns when unbracketed — so it
+    // asks for a mutable copy when the text holds any of them. Most pastes hold
+    // none and encode straight out of the clipboard's own buffer, so the copy
+    // is made only when the borrowed attempt says it needs one. Treating that
+    // request as a failure, as this did, dropped every paste carrying an escape
+    // or a tab-completion artifact.
+    var owned: ?[]u8 = null;
+    defer if (owned) |buf| self.alloc.free(buf);
+
+    const parts = vt.input.encodePaste(text, opts) catch |err| switch (err) {
+        error.MutableRequired => parts: {
+            const buf = self.alloc.dupe(u8, text) catch |e| {
+                std.log.warn("paste copy failed: {s}", .{@errorName(e)});
                 return;
             };
-    for (parts) |part| self.session.write(part);
+            owned = buf;
+            break :parts vt.input.encodePaste(buf, opts);
+        },
+    };
+
+    // Written before `owned` is freed: the pty write is a synchronous
+    // `write(2)` loop, so nothing holds on to these slices afterwards.
+    for (parts) |part| {
+        if (part.len > 0) self.session.write(part);
+    }
 }
 
 // -------------------------------------------------------------------------

src/paste.zig

@@ -0,0 +1,83 @@
+//! Whether a paste is safe to hand to the child, and how to encode it.
+//!
+//! Its own file, off GTK, for the reason the other roots here are: the
+//! decision is text in, verdict out, and it is the half of pasting that can be
+//! wrong without anything looking wrong — a refused paste is silent, and the
+//! terminal it was aimed at just sits there. The clipboard round trip above it
+//! is GTK's and wants a display; this part does not.
+
+const std = @import("std");
+const vt = @import("ghostty-vt");
+
+/// Whether text must be refused rather than typed into the child.
+///
+/// The answer turns on bracketed paste, and getting that wrong in the
+/// permissive direction is what makes this worth a function. Bracketed, the
+/// text arrives fenced: the program reads it as data, so a newline in it is a
+/// newline and not an Enter that runs whatever came before. The only thing left
+/// to refuse is a closing fence *inside* the text, which would end the bracket
+/// early and let everything after it run as though typed.
+///
+/// Unbracketed there is no fence, so a newline really is an Enter and
+/// libghostty's own test — no newline, no stray fence — is the one that
+/// applies.
+pub fn isUnsafe(text: []const u8, bracketed: bool) bool {
+    if (bracketed) return std.mem.indexOf(u8, text, end_fence) != null;
+    return !vt.input.isSafePaste(text);
+}
+
+/// The sequence that closes a bracketed paste. Never trusted inside one.
+const end_fence = "\x1b[201~";
+
+test "bracketed pastes carry newlines, which is the point of bracketing" {
+    try std.testing.expect(!isUnsafe("one\ntwo\nthree", true));
+    try std.testing.expect(!isUnsafe("cd /tmp && ls\n", true));
+}
+
+test "a closing fence is refused even bracketed" {
+    try std.testing.expect(isUnsafe("ls\x1b[201~rm -rf /\n", true));
+}
+
+test "unbracketed, a newline is an Enter and is refused" {
+    try std.testing.expect(isUnsafe("one\ntwo", false));
+    try std.testing.expect(isUnsafe("ls\x1b[201~x", false));
+}
+
+test "plain text pastes either way" {
+    for ([_]bool{ true, false }) |bracketed| {
+        try std.testing.expect(!isUnsafe("hello", bracketed));
+        try std.testing.expect(!isUnsafe("", bracketed));
+    }
+}
+
+test "text needing no rewriting encodes without a copy" {
+    const parts = try vt.input.encodePaste(@as([]const u8, "hello"), .{ .bracketed = true });
+    try std.testing.expectEqualStrings("\x1b[200~", parts[0]);
+    try std.testing.expectEqualStrings("hello", parts[1]);
+    try std.testing.expectEqualStrings("\x1b[201~", parts[2]);
+}
+
+test "an escape in the text asks for a mutable copy, and encodes once given one" {
+    // The case the terminal used to drop: encoding rewrites these bytes in
+    // place, so borrowed text is declined rather than mangled, and the caller
+    // is expected to copy and come back.
+    const text = "before\x1bafter";
+    try std.testing.expectError(
+        error.MutableRequired,
+        vt.input.encodePaste(@as([]const u8, text), .{ .bracketed = true }),
+    );
+
+    const buf = try std.testing.allocator.dupe(u8, text);
+    defer std.testing.allocator.free(buf);
+    const parts = vt.input.encodePaste(buf, .{ .bracketed = true });
+    try std.testing.expectEqualStrings("before after", parts[1]);
+}
+
+test "unbracketed newlines become carriage returns once copied" {
+    const buf = try std.testing.allocator.dupe(u8, "one\ntwo");
+    defer std.testing.allocator.free(buf);
+    const parts = vt.input.encodePaste(buf, .{ .bracketed = false });
+    try std.testing.expectEqualStrings("", parts[0]);
+    try std.testing.expectEqualStrings("one\rtwo", parts[1]);
+    try std.testing.expectEqualStrings("", parts[2]);
+}