go/importer: better error messages when export data is not found

Fixes #17281.

Change-Id: I4e639998dbe3baa98879f1becc37d7c4d19351e7
Reviewed-on: https://go-review.googlesource.com/30473
Reviewed-by: Alan Donovan <adonovan@google.com>

diff --git a/src/go/internal/gcimporter/exportdata.go b/src/go/internal/gcimporter/exportdata.go
index 4c0d2fe7616588859cd4792017341909242bc462..c12e459c3db1b937f8b8890300029c490b28b83f 100644 (file)
--- a/src/go/internal/gcimporter/exportdata.go
+++ b/src/go/internal/gcimporter/exportdata.go
@@ -8,7 +8,6 @@ package gcimporter
 
 import (
        "bufio"
-       "errors"
        "fmt"
        "io"
        "strconv"
@@ -29,7 +28,7 @@ func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
        s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
        size, err = strconv.Atoi(s)
        if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
-               err = errors.New("invalid archive header")
+               err = fmt.Errorf("invalid archive header")
                return
        }
        name = strings.TrimSpace(string(hdr[:16]))
@@ -46,6 +45,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
        // Read first line to make sure this is an object file.
        line, err := r.ReadSlice('\n')
        if err != nil {
+               err = fmt.Errorf("can't find export data (%v)", err)
                return
        }
 
@@ -58,13 +58,14 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
 
                // First entry should be __.PKGDEF.
                if name != "__.PKGDEF" {
-                       err = errors.New("go archive is missing __.PKGDEF")
+                       err = fmt.Errorf("go archive is missing __.PKGDEF")
                        return
                }
 
                // Read first line of __.PKGDEF data, so that line
                // is once again the first line of the input.
                if line, err = r.ReadSlice('\n'); err != nil {
+                       err = fmt.Errorf("can't find export data (%v)", err)
                        return
                }
        }
@@ -72,7 +73,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
        // Now at __.PKGDEF in archive or still at beginning of file.
        // Either way, line should begin with "go object ".
        if !strings.HasPrefix(string(line), "go object ") {
-               err = errors.New("not a go object file")
+               err = fmt.Errorf("not a Go object file")
                return
        }
 
@@ -80,6 +81,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
        // Begins after first line starting with $$.
        for line[0] != '$' {
                if line, err = r.ReadSlice('\n'); err != nil {
+                       err = fmt.Errorf("can't find export data (%v)", err)
                        return
                }
        }