more std lib async I/O integration

 * `zig test` gainst `--test-evented-io` parameter and gains the ability
   to seamlessly run async tests.
 * `std.ChildProcess` opens its child process pipe with O_NONBLOCK when
   using evented I/O
 * `std.io.getStdErr()` gives a File that is blocking even in evented
   I/O mode.
 * Delete `std.event.fs`. The functionality is now merged into `std.fs`
   and async file system access (using a dedicated thread) is
   automatically handled.
 * `std.fs.File` can be configured to specify whether its handle is
   expected to block, and whether that is OK to block even when in
   async I/O mode. This makes async I/O work correctly for e.g. the
   file system as well as network.
 * `std.fs.File` has some deprecated functions removed.
 * Missing readv,writev,pread,pwrite,preadv,pwritev functions are added
   to `std.os` and `std.fs.File`. They are all integrated with async
   I/O.
 * `std.fs.Watch` is still bit rotted and needs to be audited in light
   of the new async/await syntax.
 * `std.io.OutStream` integrates with async I/O
 * linked list nodes in the std lib have default `null` values for
   `prev` and `next`.
 * Windows async I/O integration is enabled for reading/writing file
   handles.
 * Added `std.os.mode_t`. Integer sizes need to be audited.
 * Fixed #4403 which was causing compiler to crash.

This is working towards:

./zig test ../test/stage1/behavior.zig --test-evented-io

Which does not successfully build yet. I'd like to enable behavioral
tests and std lib tests with --test-evented-io in the test matrix in the
future, to prevent regressions.

1 files changed, 24 insertions, 2 deletions

diff --git a/lib/std/special/test_runner.zig b/lib/std/special/test_runner.zig
index 4ba2e3aa7e..6dd208e3b4 100644
--- a/lib/std/special/test_runner.zig
+++ b/lib/std/special/test_runner.zig
@@ -2,7 +2,7 @@ const std = @import("std");
 const io = std.io;
 const builtin = @import("builtin");
 
-pub const io_mode = builtin.test_io_mode;
+pub const io_mode: io.Mode = builtin.test_io_mode;
 
 pub fn main() anyerror!void {
     const test_fn_list = builtin.test_functions;
@@ -14,6 +14,11 @@ pub fn main() anyerror!void {
         error.TimerUnsupported => @panic("timer unsupported"),
     };
 
+    var async_frame_buffer: []align(std.Target.stack_align) u8 = undefined;
+    // TODO this is on the next line (using `undefined` above) because otherwise zig incorrectly
+    // ignores the alignment of the slice.
+    async_frame_buffer = &[_]u8{};
+
     for (test_fn_list) |test_fn, i| {
         std.testing.base_allocator_instance.reset();
 
@@ -23,7 +28,24 @@ pub fn main() anyerror!void {
         if (progress.terminal == null) {
             std.debug.warn("{}/{} {}...", .{ i + 1, test_fn_list.len, test_fn.name });
         }
-        if (test_fn.func()) |_| {
+        const result = if (test_fn.async_frame_size) |size| switch (io_mode) {
+            .evented => blk: {
+                if (async_frame_buffer.len < size) {
+                    std.heap.page_allocator.free(async_frame_buffer);
+                    async_frame_buffer = try std.heap.page_allocator.alignedAlloc(u8, std.Target.stack_align, size);
+                }
+                const casted_fn = @ptrCast(async fn () anyerror!void, test_fn.func);
+                break :blk await @asyncCall(async_frame_buffer, {}, casted_fn);
+            },
+            .blocking => {
+                skip_count += 1;
+                test_node.end();
+                progress.log("{}...SKIP (async test)\n", .{test_fn.name});
+                if (progress.terminal == null) std.debug.warn("SKIP (async test)\n", .{});
+                continue;
+            },
+        } else test_fn.func();
+        if (result) |_| {
             ok_count += 1;
             test_node.end();
             std.testing.allocator_instance.validate() catch |err| switch (err) {