go/packages: allow Load to use source if no export data is possible

We ask the underlying tool to produce export data if needed, but if it
cant we should fall back to source rather than just failing.

Change-Id: I376d41b4c8ad4d3c1aef3ca4ab4e3d0466b83b56
Reviewed-on: https://go-review.googlesource.com/126875
Run-TryBot: Ian Cottrell <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: ianthehat

go/packages/packages.go

@@ -17,9 +17,10 @@ import (
 	"os"
 	"sync"
 
-	"golang.org/x/tools/go/gcexportdata"
 	"path/filepath"
 	"strings"
+
+	"golang.org/x/tools/go/gcexportdata"
 )
 
 // A LoadMode specifies the amount of detail to return when loading packages.
@@ -296,11 +297,6 @@ func (ld *loader) load(patterns ...string) ([]*Package, error) {
 	// See if the extra process invocation can be avoided.
 	list, err := listfunc(rawCfg, patterns...)
 	if _, ok := err.(GoTooOldError); ok {
-		if ld.Config.Mode >= LoadTypes {
-			// Upgrade to LoadAllSyntax because we can't depend on the existance
-			// of export data. We can remove this once iancottrell's cl is in.
-			ld.Config.Mode = LoadAllSyntax
-		}
 		listfunc = golistPackagesFallback
 		list, err = listfunc(rawCfg, patterns...)
 	}
@@ -358,8 +354,7 @@ func (ld *loader) loadFrom(list ...*rawPackage) ([]*Package, error) {
 				GoFiles:    pkg.GoFiles,
 				OtherFiles: pkg.OtherFiles,
 			},
-			// TODO: should needsrc also be true if pkg.Export == ""
-			needsrc: ld.Mode >= LoadAllSyntax,
+			needsrc: ld.Mode >= LoadAllSyntax || pkg.Export == "",
 		}
 		ld.pkgs[lpkg.ID] = lpkg
 		if !pkg.DepOnly {

go/packages/packages_test.go

@@ -533,13 +533,12 @@ func TestTypeCheckError(t *testing.T) {
 		wantTypes    bool
 		wantSyntax   bool
 		wantIllTyped bool
-		wantErrs     []string
 	}{
-		{"a", true, true, true, nil},
-		{"b", true, true, true, nil},
-		{"c", true, true, true, []string{"could not import d (no export data file)"}},
-		{"d", false, false, true, nil},  // missing export data
-		{"e", false, false, false, nil}, // type info not requested (despite type error)
+		{"a", true, true, true},
+		{"b", true, true, true},
+		{"c", true, true, true},
+		{"d", false, false, true},  // missing export data
+		{"e", false, false, false}, // type info not requested (despite type error)
 	} {
 		if usesOldGolist && test.id == "c" || test.id == "d" || test.id == "e" {
 			// Behavior is different for old golist because it upgrades to wholeProgram.
@@ -568,9 +567,6 @@ func TestTypeCheckError(t *testing.T) {
 		if p.IllTyped != test.wantIllTyped {
 			t.Errorf("IllTyped was %t for %s", p.IllTyped, test.id)
 		}
-		if errs := errorMessages(p.Errors); !reflect.DeepEqual(errs, test.wantErrs) {
-			t.Errorf("in package %s, got errors %s, want %s", p, errs, test.wantErrs)
-		}
 	}
 
 	// Check value of constant.