std.testing: add methods tmpDirPath, getTestArgs, buildExe

[matu3ba]

continuation of #11093 to simplify testing IPC

• use cases
  • get path to temporary directory
  • get the test arguments inside test block for reusage
  • build executables from text within test blocks, ie to test IPC
• missing conventions
  • how to name and debug test cases
  • where do simple+repititve build commands for testing belong

[matu3ba]

Question for next PR: Should there be a method to create a zig program from a string inside tests or where should it reside?
I woudl envision such a method to contain something along the following with an interface buildExeInTmp(allocator, progstr, binfile) ![]const u8 and the exe as return value.

    var it = try std.process.argsWithAllocator(allocator);
    const testargs = try testing.getTestArgs(&it);
    defer it.deinit(); // no-op unless WASI or Windows

    var tmp = testing.tmpDir(.{ .no_follow = true }); // ie zig-cache/tmp/8DLgoSEqz593PAEE
    defer tmp.cleanup();
    const tmpdirpath = try testing.tmpDirPath(allocator, &tmp);
    defer allocator.free(tmpdirpath);
    const child_name = "child"; // no need for suffixes (.exe, .wasm) due to '-femit-bin'
    const suffix_zig = ".zig";
    const child_path = try fs.path.join(allocator, &[_][]const u8{ tmpdirpath, child_name });
    defer allocator.free(child_path);
    const child_zig = try mem.concat(allocator, u8, &[_][]const u8{ child_path, suffix_zig });
    defer allocator.free(child_zig);

    try tmp.dir.writeFile("child.zig", childstr);
    try testing.buildExe(testargs.zigexec, child_zig, child_path);

That way, building (multiple) executables to a tmp folder would be exactly 1 properly checked function from within test blocks.

Alternatively, I will implement a shortcut to obtain child_zig and child_path (that means absolute path to zig file and absolute path to binary).

[matu3ba]

Some functionality is redundant to src/test.zig, but unfortunately this is no available for user programs, because it is not part of lib/std.
Any advice how to refactor src/test.zig or how to proceed would be nice.

[iddev5]

Question for next PR:

Its a good suggestion but eventually similar functions would be needed for all other zig operations like run, buildLib etc.
What could instead be done is a function fn writeZigFileInTmp(allocator, progstr, binfile) ![]const u8 which would return the final path of file (which is child_zig) in your test, on which we can then manually do std.fs.path.dirname(child_zig).? to get child_path.

[matu3ba]

@iddev5 With your proposed solution I get

    const zigfile_path = try tmp.writeZigFile(std.testing.allocator, childstr, child_name);
    defer std.testing.allocator.free(zigfile_path);
    const binary = zigfile_path[0 .. zigfile_path.len - 4]; // '.zig' is 4 characters
    try testing.buildExe(testargs.zigexec, zigfile_path, binary);

because we still need the path to the resulting binary for buildExe.
I think requiring to copy paste from users with an example for the subslice should be fine, since
we cant do it more efficiently than the subslice.