more compatible frame

go.mod

@@ -2,4 +2,7 @@ module github.com/jbowes/vice
 
 go 1.12
 
-require golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
+require (
+	github.com/pkg/errors v0.9.1
+	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
+)

go.sum

@@ -1,2 +1,4 @@
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

skip/error.go

@@ -1,10 +1,6 @@
 package skip
 
-import (
-	"fmt"
-
-	"golang.org/x/xerrors"
-)
+import "fmt"
 
 // New returns an error that formats as the given text, and implements the
 // behaviour described by the given Vice. The argument skip is the number of
@@ -97,7 +93,7 @@ func Sealf(err error, v Vice, skip uint, format string, a ...interface{}) error
 }
 
 func sealed(serr *sealError, v Vice, skip uint) error {
-	serr.frame = xerrors.Caller(int(2 + skip))
+	serr.frame = caller(int(2 + skip))
 	switch v {
 	case Timeout:
 		return &timeoutSeal{*serr}
@@ -129,7 +125,7 @@ func sealed(serr *sealError, v Vice, skip uint) error {
 }
 
 func wrapped(werr *wrapError, v Vice, skip uint) error {
-	werr.frame = xerrors.Caller(int(2 + skip))
+	werr.frame = caller(int(2 + skip))
 	switch v {
 	case Timeout:
 		return &timeoutWrap{*werr}
@@ -163,17 +159,10 @@ func wrapped(werr *wrapError, v Vice, skip uint) error {
 type sealError struct {
 	msg   string
 	err   error
-	frame xerrors.Frame
+	frame frame
 }
 
-func (e *sealError) Error() string              { return fmt.Sprint(e) }
-func (e *sealError) Format(s fmt.State, v rune) { xerrors.FormatError(e, s, v) }
-
-func (e *sealError) FormatError(p xerrors.Printer) (next error) {
-	p.Print(e.msg)
-	e.frame.Format(p)
-	return e.err
-}
+func (e *sealError) Error() string { return fmt.Sprint(e) }
 
 type wrapError struct {
 	sealError

skip/frame.go

@@ -0,0 +1,26 @@
+// frame reimplements stack frame handling in a way that is compatible with
+// multiple error ecosystems.
+
+package skip
+
+import "runtime"
+
+type frame [3]uintptr
+
+func caller(skip int) frame {
+	var f frame
+	runtime.Callers(skip+1, f[:])
+	return f
+}
+
+func (f frame) detail() (string, string, int) {
+	frs := runtime.CallersFrames(f[:])
+
+	if _, ok := frs.Next(); ok {
+		if fr, ok := frs.Next(); ok {
+			return fr.Function, fr.File, fr.Line
+		}
+	}
+
+	return "", "", 0
+}

skip/xerrors.go

@@ -0,0 +1,34 @@
+// This file holds xerrors specific logic. xerrors was meant to be the
+// behaviour that would land in the standard library in go 1.13. Not all
+// of it did, but this still remains the default for vice. Still, it is kept
+// in its own file to make it easier to remove or put behind a build tag.
+
+package skip
+
+import (
+	"fmt"
+
+	"golang.org/x/xerrors"
+)
+
+func (e *sealError) Format(s fmt.State, v rune) { xerrors.FormatError(e, s, v) }
+
+func (e *sealError) FormatError(p xerrors.Printer) (next error) {
+	p.Print(e.msg)
+	e.frame.Format(p)
+	return e.err
+}
+
+func (f frame) Format(p xerrors.Printer) {
+	if !p.Detail() {
+		return
+	}
+
+	fn, file, line := f.detail()
+	if fn != "" {
+		p.Printf("%s\n    ", fn)
+	}
+	if file != "" {
+		p.Printf("%s:%d\n", file, line)
+	}
+}