Only obfuscate required identifiers (#79)

The following identifiers are now skipped,
because they never show up in the binary:

- constant identifiers
- identifiers of local variables
(includes function params and named returns)
- identifiers of local types

main.go

@@ -730,11 +730,6 @@ func transformGo(file *ast.File, info *types.Info, blacklist map[types.Object]st
 		}
 		obj := info.ObjectOf(node)
 		if obj == nil {
-			switch cursor.Parent().(type) {
-			case *ast.AssignStmt:
-				// symbolic var v in v := expr.(type)
-				node.Name = hashWith(buildInfo.buildID, node.Name)
-			}
 			return true
 		}
 		pkg := obj.Pkg()
@@ -771,8 +766,17 @@ func transformGo(file *ast.File, info *types.Info, blacklist map[types.Object]st
 				// encoding/json without struct tags
 				return true
 			}
-		case *types.Const:
+
+			if obj.Parent() != pkg.Scope() {
+				// identifiers of non-global variables never show up in the binary
+				return true
+			}
+
 		case *types.TypeName:
+			if obj.Parent() != pkg.Scope() {
+				// identifiers of non-global types never show up in the binary
+				return true
+			}
 		case *types.Func:
 			sign := obj.Type().(*types.Signature)
 			if obj.Exported() && sign.Recv() != nil {

testdata/scripts/syntax.txt

@@ -1,9 +1,20 @@
-garble build main.go
-exec ./main
+go build
+exec ./main$exe
 cmp stderr main.stderr
 
-! binsubstr main$exe 'valuable information'
+binsubstr main$exe 'globalVar' # 'globalType' only matches on go < 1.15 
+! binsubstr main$exe 'localName' 'globalConst'
 
+garble -debugdir=debug build
+exec ./main$exe
+cmp stderr main.stderr
+
+! binsubstr main$exe 'localName' 'globalConst' 'globalVar' 'globalType' 'valuable information'
+
+binsubstr debug/main/z1.go 'localName' 'globalConst'
+
+-- go.mod --
+module test/main
 -- main.go --
 package main
 
@@ -53,7 +64,41 @@ func main() {
 
 	enc, _ := json.Marshal(EncodingT{Foo: 3})
 	println(string(enc))
+	scopesTest()
+}
+
+-- scopes.go --
+package main
+
+const globalConst = 1
+
+type globalType int
+
+var (
+	globalVar                 = 1
+	globalVarTyped globalType = 1
+)
+
+func scopesTest() {
+	println(globalVar, globalConst, globalVarTyped)
+	const localNameConst = 1
+
+	localNameShort := 4
+
+	type localNameType int
+
+	var (
+		localNameVar                   = 5
+		localNameTypeVar localNameType = 1
+	)
+
+	println(localNameConst, localNameShort, localNameVar, localNameTypeVar, input("input"))
 }
+
+func input(localNameParam string) (localNameReturn string) { return localNameParam }
+
 -- main.stderr --
 nil case
 {"Foo":3}
+1 1 1
+1 4 5 1 input