Build: Print return traces from BuildStep errors

[Parzival-3141]

Closes #14961

// RunStep.zig
fn make(step: *Step, prog_node: *std.Progress.Node) !void {
    try std.testing.expect(false);
    // ...

Before:

C:\zigsrc\zig\build\stage4\bin\zig.exe build run
run compiler-testing: error: TestUnexpectedResult

After:

C:\zigsrc\zig\build\stage4\bin\zig.exe build run
run compiler-testing: error: step failed with error TestUnexpectedResult:
C:\zigsrc\zig\lib\std\testing.zig:509:14: 0x7ff6bcec10b7 in expect (build.exe.obj)
    if (!ok) return error.TestUnexpectedResult;
             ^
C:\zigsrc\zig\lib\std\Build\RunStep.zig:372:5: 0x7ff6bce9799d in make (build.exe.obj)
    try std.testing.expect(false);
    ^

If the return trace is too long and fills the internal buffer, we print the partial trace and a message notifying the user.

// RunStep.zig
fn fib(n: u32) !u32 {
    if (n <= 1) return n;
    if (n == 21) return error.Fibbage;
    return try fib(n - 1) + try fib(n - 2);
}

fn make(step: *Step, prog_node: *std.Progress.Node) !void {
    _ = try fib(55);
   // ...

C:\zigsrc\zig\build\stage4\bin\zig.exe build run
run compiler-testing: error: step failed with error Fibbage:
C:\zigsrc\zig\lib\std\Build\RunStep.zig:373:18: 0x7ff6298a1110 in fib (build.exe.obj)
    if (n == 21) return error.Fibbage;
                 ^
C:\zigsrc\zig\lib\std\Build\RunStep.zig:374:12: 0x7ff6298a118b in fib (build.exe.obj)
    return try fib(n - 1) + try fib(n - 2);
           ^
C:\zigsrc\zig\lib\std\Build\RunStep.zig:374:12: 0x7ff6298a118b in fib (build.exe.obj)
    return try fib(n - 1) + try fib(n - 2);
           ^
C:\zigsrc\zig\lib\std\Build\RunStep.zig:374:12: 0x7ff6298a118b in fib (build.exe.obj)
    return try fib(n - 1) + try fib(n - 2);
           ^
// etc....
C:\zigsrc\zig\lib\std\Build\RunStep.zig:374:12: 0x7ff6298a118b in fib (build.exe.obj)
    return try fib(n - 1) + try fib(n - 2);
           ^
C:\zigsrc\zig\lib.... errorReturnTrace exceeds buffer size!

I'm assuming 4096 chars is more than enough for most people, and I call Allocator.resize() to trim unused space.

[Parzival-3141]

Not really sure why the aarch64-linux-release test failed. Seems like some other commits failed in the same way.

[andrewrk]

Thanks for working on this.

It's a nice idea, but it serializes too early. Instead, it should capture the trace and store that data, serializing it later when errors are printed to the terminal.

[Parzival-3141]

I'm guessing this could be implemented through the ErrorBundle field, but I'm not sure how to achieve that and could use some guidance. The current patch works as intended though and can be merged if sufficient.