cmd/compile: reintroduce support for version 0 export format

The Go1.7 export format didn't encode the field package for
blank struct fields (#15514). Re-introduce support for that
format so we can read it w/o error.

For #16881.

Change-Id: Ib131d41aac56dbf970aab15ae7e75ef3944b412d
Reviewed-on: https://go-review.googlesource.com/27912
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/compile/internal/gc/bimport.go b/src/cmd/compile/internal/gc/bimport.go
index 39fa844457825846adb9287ef5cb5190a21c3c78..99c8554729a7adda34e0e7f05a6495dac36bd573 100644 (file)
--- a/src/cmd/compile/internal/gc/bimport.go
+++ b/src/cmd/compile/internal/gc/bimport.go
@@ -623,6 +623,11 @@ func (p *importer) method() *Node {
 // parser.go:sym,hidden_importsym
 func (p *importer) fieldName() *Sym {
        name := p.string()
+       if p.version == 0 && name == "_" {
+               // version 0 didn't export a package for _ fields
+               // but used the builtin package instead
+               return builtinpkg.Lookup(name)
+       }
        pkg := localpkg
        if name != "" && !exportname(name) {
                if name == "?" {