better error tracking

3 files changed, 80 insertions, 16 deletions

diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..681ef4f
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,52 @@
+package main
+
+import (
+	"os/exec"
+	"strings"
+)
+
+type ProcessError struct {
+	*exec.ExitError
+	Cmd string
+}
+
+func (e *ProcessError) Error() string {
+	lines := strings.Split(string(e.ExitError.Stderr), "\n")
+	if lines[len(lines)-1] == "" {
+		lines = lines[:len(lines)-1]
+	}
+	ret := e.Cmd + ": " + e.ExitError.Error()
+	if len(lines) > 0 {
+		ret += ":\n > " + strings.Join(lines, "\n > ")
+	}
+	return ret
+}
+
+type ErrorCollector struct {
+	errs []error
+}
+
+func (ec ErrorCollector) Error() string {
+	lines := make([]string, len(ec.errs))
+	for i := range ec.errs {
+		lines[i] = ec.errs[i].Error()
+	}
+	return strings.Join(lines, "\n")
+}
+
+func (ec *ErrorCollector) Add(err error) {
+	if err != nil {
+		ec.errs = append(ec.errs, err)
+	}
+}
+
+func (ec ErrorCollector) Err() error {
+	switch len(ec.errs) {
+	case 0:
+		return nil
+	case 1:
+		return ec.errs[0]
+	default:
+		return ec
+	}
+}
diff --git a/filter.go b/filter.go
index ea6a89e..1ff34ac 100644
--- a/filter.go
+++ b/filter.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"bytes"
-	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
@@ -11,6 +10,7 @@ import (
 	"strings"
 
 	"git.lukeshu.com/go/libfastimport"
+	"github.com/pkg/errors"
 )
 
 type fullcommit struct {
@@ -86,7 +86,7 @@ func (f *Filter) pkgbuild2srcinfo(pkgbuildId string) (string, error) {
 			return "", err
 		}
 		if sha1 != pkgbuildId {
-			return "", fmt.Errorf("PKGBUILD sha1 mismatch: %q != %q", pkgbuildId, sha1)
+			return "", errors.Errorf("PKGBUILD sha1 mismatch: %q != %q", pkgbuildId, sha1)
 		}
 		// Write the PKGBUILD to a temporary file to pass to makepkg
 		file, err := os.OpenFile(f.infofile("tmp/PKGBUILD"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
@@ -103,7 +103,7 @@ func (f *Filter) pkgbuild2srcinfo(pkgbuildId string) (string, error) {
 		cmd.Dir = f.infofile("tmp")
 		srcinfoBody, err := cmd.Output()
 		if err != nil {
-			return "", err
+			return "", &ProcessError{ExitError: err.(*exec.ExitError), Cmd: "makepkg --printsrcinfo"}
 		}
 		// Write the .SRCINFO back in to git
 		mark := f.newmark()
@@ -164,7 +164,7 @@ func (f *Filter) Run() error {
 			}
 			cmd, err := f.frontend.ReadCmd()
 			if cmd != nil || err != io.EOF {
-				return fmt.Errorf("git fast-export kept going after 'done': cmd=%v err=%v", cmd, err)
+				return errors.Errorf("git fast-export kept going after 'done': cmd=%v err=%v", cmd, err)
 			}
 			return nil
 		case libfastimport.CmdReset:
@@ -263,7 +263,7 @@ func (f *Filter) Run() error {
 			branch_ref := f.toPfx + "/" + branchname
 			from_dataref, from_dataref_ok := f.refs[branch_ref]
 			if !from_dataref_ok {
-				return fmt.Errorf("cannot delete file %q from branch %q, because that branch doesn't exist!", cmdt.Path, branchname)
+				return errors.Errorf("cannot delete file %q from branch %q, because that branch doesn't exist!", cmdt.Path, branchname)
 			}
 			file_mode, _, _, err := f.backend.Ls(libfastimport.CmdLs{DataRef: from_dataref, Path: cmdt.Path})
 			if err != nil {
diff --git a/git.go b/git.go
index c6509ff..09622b3 100644
--- a/git.go
+++ b/git.go
@@ -2,12 +2,12 @@ package main
 
 import (
 	"bytes"
-	"fmt"
 	"os"
 	"os/exec"
 	"strings"
 
 	"git.lukeshu.com/go/libfastimport"
+	"github.com/pkg/errors"
 )
 
 func gitFastExport(args ...string) (*libfastimport.Frontend, error) {
@@ -27,13 +27,19 @@ func gitFastExport(args ...string) (*libfastimport.Frontend, error) {
 	}
 
 	frontend := libfastimport.NewFrontend(stdout, nil, func(err error) error {
-		if _err := cmd.Wait(); _err != nil {
-			if ee, ok := _err.(*exec.ExitError); ok {
+		errs := ErrorCollector{}
+
+		errs.Add(err)
+
+		if err := cmd.Wait(); err != nil {
+			if ee, ok := err.(*exec.ExitError); ok {
 				ee.Stderr = stderr.Bytes()
+				err = &ProcessError{ExitError: ee, Cmd: "git fast-export"}
 			}
-			err = _err
+			errs.Add(err)
 		}
-		return err
+
+		return errs.Err()
 	})
 
 	return frontend, nil
@@ -66,15 +72,21 @@ func gitFastImport(args ...string) (*libfastimport.Backend, error) {
 	pipw.Close()
 
 	backend := libfastimport.NewBackend(stdin, pipr, func(err error) error {
-		pipr.Close()
+		errs := ErrorCollector{}
+
+		errs.Add(err)
+
 		stdin.Close()
-		if _err := cmd.Wait(); _err != nil {
-			if ee, ok := _err.(*exec.ExitError); ok {
+		pipr.Close()
+		if err = cmd.Wait(); err != nil {
+			if ee, ok := err.(*exec.ExitError); ok {
 				ee.Stderr = stderr.Bytes()
+				err = &ProcessError{ExitError: ee, Cmd: "git fast-import"}
 			}
-			err = _err
+			errs.Add(err)
 		}
-		return err
+
+		return errs.Err()
 	})
 
 	return backend, nil
@@ -95,7 +107,7 @@ func gitRefs() (map[string]string, error) {
 		sp := strings.IndexByte(line, ' ')
 		ht := strings.IndexByte(line, '\t')
 		if sp < 0 || ht < sp {
-			return nil, fmt.Errorf("malformed git for-each-ref line: %q", line)
+			return nil, errors.Errorf("malformed git for-each-ref line: %q", line)
 		}
 		refTarget := line[:sp]
 		refType := line[sp+1 : ht]