cmd/compile/internal/types2: record error code in Error struct

go/types already does this, if slightly differently.

Change-Id: I9cf5f493714d865deec5ad23e2ee9b5c5d3f2f0c
Reviewed-on: https://go-review.googlesource.com/c/go/+/475197
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/api.go

@@ -27,6 +27,7 @@ import (
 	"cmd/compile/internal/syntax"
 	"fmt"
 	"go/constant"
+	. "internal/types/errors"
 	"strings"
 )
 
@@ -39,6 +40,7 @@ type Error struct {
 	Msg  string     // default error message, user-friendly
 	Full string     // full error message, for debugging (may contain internal details)
 	Soft bool       // if set, error is "soft"
+	Code Code       // error code
 }
 
 // Error returns an error string formatted as follows:

src/cmd/compile/internal/types2/errors.go

@@ -250,7 +250,7 @@ func (check *Checker) err(at poser, code Code, msg string, soft bool) {
 		pos = check.errpos
 	}
 
-	err := Error{pos, stripAnnotations(msg), msg, soft}
+	err := Error{pos, stripAnnotations(msg), msg, soft, code}
 	if check.firstErr == nil {
 		check.firstErr = err
 	}