Remove unused imports via go/types.

Fixes #481

internal/literals/literals.go

@@ -10,7 +10,6 @@ import (
 	"go/token"
 	"go/types"
 	mathrand "math/rand"
-	"strconv"
 
 	"golang.org/x/tools/go/ast/astutil"
 	ah "mvdan.cc/garble/internal/asthelper"
@@ -130,46 +129,7 @@ func Obfuscate(file *ast.File, info *types.Info, fset *token.FileSet, linkString
 		return true
 	}
 
-	// Imports which are used might be marked as unused by only looking at the ast,
-	// because packages can declare a name different from the last element of their import path.
-	//
-	// 	package main
-	//
-	// 	import "github.com/user/somepackage"
-	//
-	//	func main(){
-	//		// this line uses github.com/user/somepackage
-	//		anotherpackage.Foo()
-	//	}
-	//
-	// TODO: remove this check and detect used imports with go/types somehow
-	prevUsedImports := make(map[string]bool)
-	for _, imp := range file.Imports {
-		path, err := strconv.Unquote(imp.Path.Value)
-		if err != nil {
-			panic(err)
-		}
-		prevUsedImports[path] = astutil.UsesImport(file, path)
-	}
-
-	file = astutil.Apply(file, pre, post).(*ast.File)
-
-	// some imported constants might not be needed anymore, remove unnecessary imports
-	for _, imp := range file.Imports {
-		path, err := strconv.Unquote(imp.Path.Value)
-		if err != nil {
-			panic(err)
-		}
-		if !prevUsedImports[path] || astutil.UsesImport(file, path) {
-			continue
-		}
-
-		if !astutil.DeleteImport(fset, file, path) {
-			panic(fmt.Sprintf("cannot delete unused import: %v", path))
-		}
-	}
-
-	return file
+	return astutil.Apply(file, pre, post).(*ast.File)
 }
 
 // withPos sets any token.Pos fields under node which affect printing to pos.

main.go

@@ -1453,6 +1453,50 @@ func (tf *transformer) transformGo(file *ast.File) *ast.File {
 	// and that's not allowed in the runtime itself.
 	if flagLiterals && curPkg.ToObfuscate {
 		file = literals.Obfuscate(file, tf.info, fset, tf.linkerVariableStrings)
+
+		// some imported constants might not be needed anymore, remove unnecessary imports
+		usedImports := make(map[string]bool)
+		ast.Inspect(file, func(n ast.Node) bool {
+			node, ok := n.(*ast.Ident)
+			if !ok {
+				return true
+			}
+
+			uses, ok := tf.info.Uses[node].(*types.PkgName)
+			if !ok {
+				return true
+			}
+
+			usedImports[uses.Imported().Path()] = true
+
+			return true
+		})
+
+		for _, imp := range file.Imports {
+			if imp.Name != nil && (imp.Name.Name == "_" || imp.Name.Name == ".") {
+				continue
+			}
+
+			path, err := strconv.Unquote(imp.Path.Value)
+			if err != nil {
+				panic(err)
+			}
+
+			// The import path can't be used directly here, because the actual
+			// path resolved via go/types might be different from the naive path.
+			lpkg, err := listPackage(path)
+			if err != nil {
+				panic(err)
+			}
+
+			if usedImports[lpkg.ImportPath] {
+				continue
+			}
+
+			if !astutil.DeleteImport(fset, file, path) {
+				panic(fmt.Sprintf("cannot delete unused import: %q", path))
+			}
+		}
 	}
 
 	pre := func(cursor *astutil.Cursor) bool {

testdata/scripts/literals.txt

@@ -64,7 +64,7 @@ package main
 import (
 	_ "runtime/debug"
 
-	"test/main/imported"
+	"test/main/imp"
 )
 
 type structTest struct {
@@ -295,7 +295,7 @@ func shadowTest() {
 		println("obfuscated with shadowed builtins (types)")
 	}
 }
--- imported/imported.go --
+-- imp/imported.go --
 package imported
 
 type ImportedType int