Attempt to restore 1.3 and 1.4 compat

go13.go

@@ -3,8 +3,13 @@
 package gotool
 
 import (
+	"go/build"
 	"path/filepath"
 	"runtime"
 )
 
 var gorootSrcPkg = filepath.Join(runtime.GOROOT(), "src", "pkg")
+
+func shouldIgnoreImport(p *build.Package) bool {
+	return true
+}

go14.go

@@ -3,8 +3,13 @@
 package gotool
 
 import (
+	"go/build"
 	"path/filepath"
 	"runtime"
 )
 
 var gorootSrcPkg = filepath.Join(runtime.GOROOT(), "src")
+
+func shouldIgnoreImport(p *build.Package) bool {
+	return true
+}

go15.go

@@ -0,0 +1,16 @@
+// +build go1.5
+// +build !go1.4
+
+package gotool
+
+import (
+	"go/build"
+	"path/filepath"
+	"runtime"
+)
+
+var gorootSrcPkg = filepath.Join(runtime.GOROOT(), "src", "pkg")
+
+func shouldIgnoreImport(p *build.Package) bool {
+	return p == nil || len(p.InvalidGoFiles) == 0
+}

match.go

@@ -264,7 +264,7 @@ func matchPackagesInFS(pattern string) []string {
 		// as not matching the pattern. Go 1.5 and earlier skipped, but that
 		// behavior means people miss serious mistakes.
 		// See golang.org/issue/11407.
-		if p, err := build.ImportDir(path, 0); err != nil && (p == nil || len(p.InvalidGoFiles) == 0) {
+		if p, err := build.ImportDir(path, 0); err != nil && shouldIgnoreImport(p) {
 			if _, noGo := err.(*build.NoGoError); !noGo {
 				log.Print(err)
 			}