internal/pkgbits: add fingerprints to unified IR export format

So far unified IR has been relying on the backwards-compat iexport
data to supply package fingerprints for imports. To be able to drop
the iexport data and natively use unified IR everywhere.

This CL applies basically the same idea that iexport used: simply
hash all of the export data as it's being written out, and then tack
on an 8-byte hash at the end.

Change-Id: Iaca5fbfd7443088bc7f422a1c58be3e762c29014
Reviewed-on: https://go-review.googlesource.com/c/go/+/396196
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/src/internal/pkgbits/encoder.go b/src/internal/pkgbits/encoder.go
index 820c707940..4780f01c39 100644
--- a/src/internal/pkgbits/encoder.go
+++ b/src/internal/pkgbits/encoder.go
@@ -8,6 +8,7 @@ package pkgbits
 
 import (
 	"bytes"
+	"crypto/md5"
 	"encoding/binary"
 	"go/constant"
 	"io"
@@ -30,7 +31,10 @@ func NewPkgEncoder(syncFrames int) PkgEncoder {
 	}
 }
 
-func (pw *PkgEncoder) DumpTo(out io.Writer) {
+func (pw *PkgEncoder) DumpTo(out0 io.Writer) (fingerprint [8]byte) {
+	h := md5.New()
+	out := io.MultiWriter(out0, h)
+
 	writeUint32 := func(x uint32) {
 		assert(binary.Write(out, binary.LittleEndian, x) == nil)
 	}
@@ -57,6 +61,12 @@ func (pw *PkgEncoder) DumpTo(out io.Writer) {
 			assert(err == nil)
 		}
 	}
+
+	copy(fingerprint[:], h.Sum(nil))
+	_, err := out0.Write(fingerprint[:])
+	assert(err == nil)
+
+	return
 }
 
 func (pw *PkgEncoder) StringIdx(s string) int {