Crash when copying selection that runs to end of window

[phinze]

👋 😄 Hi! Nice terminal emulator you've got here. ✨ I've broken it for you. 🙃

Steps to reproduce (on darwin/arm64 but I'm betting it happens everywhere):

• Make a selection that runs to the end of the window
• Try to copy w/ CMD+C

Expect:

• Copied text

Observe:

• Crash

---

Stepping around with a debugger, it looks like this assertion is failing, because sel.x actually does have a value larger than the number of columns in the window.

I'm only just getting the hang of the codebase so I'm not sure if this is a bug in the selection capture code or just a quirk that we need to handle by "truncating" the selection to the end of the window.

[mitchellh]

While trying to reproduce this I figured out another crash, its odd, digging into it now:

1. cat src/Window.zig (any file that causes the screen to scroll)
2. Select any of the TRAILING blank space
3. Copy

I added some logging and the char its getting is a 2863311530 which is 0xAAAAAAAA which is what Zig sets as the undefined value for debug builds so... somewhere we're setting char to undefined. Bad! This is a diff bug since its not the assertion you're seeing tripped, but I'm going to look at this first...

[mitchellh]

Fixed my issue, now looking into yours: 9d26ab2 (Note: this case should be tested, but we're going to have to redo all the resize stuff for reflow and I'm going to get to that Soon(tm) so... ignoring)

[mitchellh]

Reproduced, here is the stack trace:

gdb $ bt
#0  0x0000fffff7e038d8 in __pthread_kill_implementation () from /nix/store/6afvzgx3himw7584k9zmfxmqd86b1z7j-glibc-2.34-210/lib/libc.so.6
#1  0x0000fffff7dc12b4 in raise () from /nix/store/6afvzgx3himw7584k9zmfxmqd86b1z7j-glibc-2.34-210/lib/libc.so.6
#2  0x0000fffff7daefd8 in abort () from /nix/store/6afvzgx3himw7584k9zmfxmqd86b1z7j-glibc-2.34-210/lib/libc.so.6
#3  0x0000000000447420 in std.os.abort () at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/os.zig:505
#4  0x0000000000444a9c in std.debug.panicImpl (trace=0x0, first_trace_addr=..., msg=...) at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/debug.zig:386
#5  0x0000000000441ddc in std.builtin.default_panic (msg=<error reading variable: Cannot access memory at address 0x6>, error_return_trace=0x0) at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/builtin.zig:844
#6  0x0000000000442690 in std.debug.assert (ok=false) at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/debug.zig:281
#7  0x000000000049027c in terminal.Screen.selectionSlices (self=..., sel=...) at /home/mitchellh/code/go/src/github.com/mitchellh/ghostty/src/terminal/Screen.zig:493
#8  0x000000000046d6d8 in terminal.Screen.selectionString (self=<error reading variable: Cannot access memory at address 0x0>, alloc=<error reading variable: Cannot access memory at address 0x6>, sel=<error reading variable: Cannot access memory at address 0x159894>)
    at /home/mitchellh/code/go/src/github.com/mitchellh/ghostty/src/terminal/Screen.zig:408
#9  0x000000000046ea50 in Window.keyCallback (window=..., key=c, scancode=54, action=press, mods=...) at Window.zig:462
#10 .glfw.Window.CWrapper.keyCallbackWrapper (handle=0xb4dc70, key=67, scancode=54, action=1, mods=8) at /home/mitchellh/code/go/src/github.com/mitchellh/ghostty/vendor/mach/glfw/src/Window.zig:2112
#11 0x0000000000512294 in _glfwInputKey (window=0xb4dc70, key=67, scancode=54, action=1, mods=8) at vendor/mach/glfw/upstream/glfw/src/input.c:305
#12 0x000000000057dbb8 in processEvent (event=0xffffffff76e8) at vendor/mach/glfw/upstream/glfw/src/x11_window.c:1206
#13 0x0000000000563bd0 in _glfwPollEventsX11 () at vendor/mach/glfw/upstream/glfw/src/x11_window.c:2735
#14 0x0000000000563f44 in _glfwWaitEventsX11 () at vendor/mach/glfw/upstream/glfw/src/x11_window.c:2759
#15 0x000000000053ed6c in glfwWaitEvents () at vendor/mach/glfw/upstream/glfw/src/window.c:1119
#16 0x00000000004467f8 in .glfw.waitEvents () at /home/mitchellh/code/go/src/github.com/mitchellh/ghostty/vendor/mach/glfw/src/main.zig:414
#17 App.run (self=...) at App.zig:95
#18 0x000000000044545c in main () at main.zig:81
#19 0x0000000000446e1c in std.start.callMain () at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/start.zig:576
#20 std.start.initEventLoopAndCallMain () at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/start.zig:510
#21 std.start.callMainWithArgs (argc=5, argv=0xffffffffa4b8, envp=...) at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/start.zig:460
#22 std.start.main (c_argc=5, c_argv=0xffffffffa4b8, c_envp=0xffffffffa4e8) at /nix/store/a44c1nv4qqwqshc5li4gk8nwd99lgr4r-zig-0.10.0-dev.3445+18440cb23/lib/zig/std/start.zig:475

[mitchellh]

Oh fun, I never thought about this but the mouse xpos ypos values can be NEGATIVE if you click and drag OFF the window (to the top/left) or greater than the width if you drag off right/bottom. Commit 1da5ca0 bounds this on both sides.

Praise assertions validating our assumptions and finding something that breaks em.