3 files changed, 28 insertions, 19 deletions
diff --git a/std/os.zig b/std/os.zig
index 3409dcf6c6..a0f8d1f12b 100644
--- a/std/os.zig
+++ b/std/os.zig
@@ -2487,7 +2487,7 @@ pub fn toPosixPath(file_path: []const u8) ![PATH_MAX]u8 {
 /// if this happens the fix is to add the error code to the corresponding
 /// switch expression, possibly introduce a new error in the error set, and
 /// send a patch to Zig.
-pub const unexpected_error_tracing = false;
+pub const unexpected_error_tracing = builtin.mode == .Debug;
 
 pub const UnexpectedError = error{
     /// The Operating System returned an undocumented error code.
diff --git a/std/special/panic.zig b/std/special/panic.zig
index 50dc5e0c65..92e0d9164c 100644
--- a/std/special/panic.zig
+++ b/std/special/panic.zig
@@ -7,8 +7,23 @@ const builtin = @import("builtin");
 const std = @import("std");
 
 pub fn panic(msg: []const u8, error_return_trace: ?*builtin.StackTrace) noreturn {
-    const stderr = std.io.getStdErr() catch std.process.abort();
-    stderr.write("panic: ") catch std.process.abort();
-    stderr.write(msg) catch std.process.abort();
-    std.process.abort();
+    @setCold(true);
+    switch (builtin.os) {
+        .freestanding => {
+            while (true) {}
+        },
+        .wasi => {
+            std.debug.warn("{}", msg);
+            _ = std.os.wasi.proc_raise(std.os.wasi.SIGABRT);
+            unreachable;
+        },
+        .uefi => {
+            // TODO look into using the debug info and logging helpful messages
+            std.os.abort();
+        },
+        else => {
+            const first_trace_addr = @returnAddress();
+            std.debug.panicExtra(error_return_trace, first_trace_addr, "{}", msg);
+        },
+    }
 }
diff --git a/std/special/test_runner.zig b/std/special/test_runner.zig
index 001b26ebb0..db01293059 100644
--- a/std/special/test_runner.zig
+++ b/std/special/test_runner.zig
@@ -2,34 +2,28 @@ const std = @import("std");
 const io = std.io;
 const builtin = @import("builtin");
 const test_fn_list = builtin.test_functions;
+const warn = std.debug.warn;
 
-pub fn main() void {
-    const stderr = io.getStdErr() catch std.process.abort();
-
+pub fn main() !void {
     var ok_count: usize = 0;
     var skip_count: usize = 0;
     for (test_fn_list) |test_fn, i| {
-        stderr.write("test ") catch std.process.abort();
-        stderr.write(test_fn.name) catch std.process.abort();
+        warn("{}/{} {}...", i + 1, test_fn_list.len, test_fn.name);
 
         if (test_fn.func()) |_| {
             ok_count += 1;
-            stderr.write("...OK\n") catch std.process.abort();
+            warn("OK\n");
         } else |err| switch (err) {
             error.SkipZigTest => {
                 skip_count += 1;
-                stderr.write("...SKIP\n") catch std.process.abort();
-            },
-            else => {
-                stderr.write("error: ") catch std.process.abort();
-                stderr.write(@errorName(err)) catch std.process.abort();
-                std.process.abort();
+                warn("SKIP\n");
             },
+            else => return err,
         }
     }
     if (ok_count == test_fn_list.len) {
-        stderr.write("All tests passed.\n") catch std.process.abort();
+        warn("All tests passed.\n");
     } else {
-        stderr.write("Some tests skipped.\n") catch std.process.abort();
+        warn("{} passed; {} skipped.\n", ok_count, skip_count);
     }
 }