cmd/compile/internal/importer: support final unified IR export format

This updates the cmd/compile/internal/importer to natively support the
"final" unified IR export format. This is really just for unit tests
and symmetry with go/internal/gcimporter though, since
cmd/compile/internal/noder has its own types2.Importer.

Change-Id: I52fbb6134dbc0a903d62c1b04f95d33bd29e0414
Reviewed-on: https://go-review.googlesource.com/c/go/+/388617
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/importer/exportdata.go

@@ -41,7 +41,9 @@ func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
 // start of the file before calling this function. The hdr result
 // is the string before the export data, either "$$" or "$$B".
 //
-func FindExportData(r *bufio.Reader) (hdr string, err error) {
+// If size is non-negative, it's the number of bytes of export data
+// still available to read from r.
+func FindExportData(r *bufio.Reader) (hdr string, size int, err error) {
 	// Read first line to make sure this is an object file.
 	line, err := r.ReadSlice('\n')
 	if err != nil {
@@ -52,7 +54,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
 	if string(line) == "!<arch>\n" {
 		// Archive file. Scan to __.PKGDEF.
 		var name string
-		if name, _, err = readGopackHeader(r); err != nil {
+		if name, size, err = readGopackHeader(r); err != nil {
 			return
 		}
 
@@ -76,6 +78,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
 		err = fmt.Errorf("not a Go object file")
 		return
 	}
+	size -= len(line)
 
 	// Skip over object header to export data.
 	// Begins after first line starting with $$.
@@ -84,6 +87,7 @@ func FindExportData(r *bufio.Reader) (hdr string, err error) {
 			err = fmt.Errorf("can't find export data (%v)", err)
 			return
 		}
+		size -= len(line)
 	}
 	hdr = string(line)
 

src/cmd/compile/internal/importer/gcimporter.go

@@ -10,6 +10,7 @@ import (
 	"cmd/compile/internal/types2"
 	"fmt"
 	"go/build"
+	"internal/pkgbits"
 	"io"
 	"io/ioutil"
 	"os"
@@ -134,9 +135,9 @@ func Import(packages map[string]*types2.Package, path, srcDir string, lookup fun
 	}
 	defer rc.Close()
 
-	var hdr string
 	buf := bufio.NewReader(rc)
-	if hdr, err = FindExportData(buf); err != nil {
+	hdr, size, err := FindExportData(buf)
+	if err != nil {
 		return
 	}
 
@@ -146,17 +147,33 @@ func Import(packages map[string]*types2.Package, path, srcDir string, lookup fun
 
 	case "$$B\n":
 		var data []byte
-		data, err = ioutil.ReadAll(buf)
+		var r io.Reader = buf
+		if size >= 0 {
+			r = io.LimitReader(r, int64(size))
+		}
+		data, err = ioutil.ReadAll(r)
 		if err != nil {
 			break
 		}
 
+		if len(data) == 0 {
+			err = fmt.Errorf("import %q: missing export data", path)
+			break
+		}
+		exportFormat := data[0]
+		s := string(data[1:])
+
 		// The indexed export format starts with an 'i'; the older
 		// binary export format starts with a 'c', 'd', or 'v'
 		// (from "version"). Select appropriate importer.
-		if len(data) > 0 && data[0] == 'i' {
+		switch exportFormat {
-			pkg, err = ImportData(packages, string(data[1:]), id)
+		case 'u':
-		} else {
+			s = s[:strings.Index(s, "\n$$\n")]
+			input := pkgbits.NewPkgDecoder(id, s)
+			pkg = ReadPackage(nil, packages, input)
+		case 'i':
+			pkg, err = ImportData(packages, s, id)
+		default:
 			err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
 		}