syscall: add DLLError.Unwrap function

Because we're expecting for future functions to be unavailable, we
should add an Unwrap() function to the DLLError struct, so that people
can test for this situation easily via:

    if errors.Is(err, syscall.ERROR_PROC_NOT_FOUND) { ... }

DLLError already was wrapping the underlying Errno error, but never got
the Go 1.13 helper method.

Fixes golang/go#42584

Change-Id: I0f32a5146946b1b37a30897ba825a56faefc792c
Reviewed-on: https://go-review.googlesource.com/c/go/+/269761
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/doc/go1.16.html b/doc/go1.16.html
index a2f39893be919bb1b5aef0ed36044a9df89dbcf3..92cadff7138403742aa8ff05f3a968f04f9acace 100644 (file)
--- a/doc/go1.16.html
+++ b/doc/go1.16.html
@@ -501,6 +501,10 @@ Do not send CLs removing the interior tags from such phrases.
     <p><!-- CL 261917 -->
       <a href="/pkg/syscall/#SysProcAttr"><code>SysProcAttr</code></a> on Windows has a new NoInheritHandles field that disables inheriting handles when creating a new process.
     </p>
+
+    <p><!-- CL 269761, golang.org/issue/42584 -->
+      <a href="/pkg/syscall/#DLLError"><code>DLLError</code></a> on Windows now has an Unwrap function for unwrapping its underlying error.
+    </p>
   </dd>
 </dl><!-- syscall -->
 

diff --git a/src/syscall/dll_windows.go b/src/syscall/dll_windows.go
index c54feec56aec2d6963729df6e5694c7710850d5f..d99da000896f74bd17e3f1dfe23bfe8564f84352 100644 (file)
--- a/src/syscall/dll_windows.go
+++ b/src/syscall/dll_windows.go
@@ -20,6 +20,8 @@ type DLLError struct {
 
 func (e *DLLError) Error() string { return e.Msg }
 
+func (e *DLLError) Unwrap() error { return e.Err }
+
 // Implemented in ../runtime/syscall_windows.go.
 
 func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)