reduce false positives of sliceInitialLength

sliceinitiallength/slicemutation.go

@@ -2,6 +2,7 @@ package sliceinitiallength
 
 import (
 	"go/ast"
+	"go/token"
 	"go/types"
 
 	"github.com/seiyab/gost/utils"
@@ -13,6 +14,7 @@ type mutation int
 const (
 	appended mutation = iota + 1
 	assigned
+	replaced
 	copied
 	mixed
 )
@@ -62,17 +64,21 @@ func collectSliceMutations(pass *analysis.Pass) map[types.Object]mutation {
 }
 
 func visitAssign(n *ast.AssignStmt, pass *analysis.Pass) map[types.Object]mutation {
+	if n.Tok != token.ASSIGN {
+		return nil
+	}
 	var muts = make(map[types.Object]mutation)
 	for i, lhs := range n.Lhs {
 		if i >= len(n.Rhs) {
 			break
 		}
-		if ident, ok := lhs.(*ast.Ident); ok {
-			t := pass.TypesInfo.TypeOf(ident)
+		switch lhs := lhs.(type) {
+		case *ast.Ident:
+			t := pass.TypesInfo.TypeOf(lhs)
 			if t == nil {
 				continue
 			}
-			o := pass.TypesInfo.ObjectOf(ident)
+			o := pass.TypesInfo.ObjectOf(lhs)
 			if o == nil {
 				continue
 			}
@@ -81,17 +87,26 @@ func visitAssign(n *ast.AssignStmt, pass *analysis.Pass) map[types.Object]mutati
 			}
 			call, ok := n.Rhs[i].(*ast.CallExpr)
 			if !ok {
+				muts[o] = replaced
 				continue
 			}
 			if !appendMatcher.Matches(pass, call) {
+				muts[o] = replaced
+				continue
+			}
+			orig, ok := call.Args[0].(*ast.Ident)
+			if !ok {
+				muts[o] = replaced
+				continue
+			}
+			if pass.TypesInfo.ObjectOf(orig) != o {
+				muts[o] = replaced
 				continue
 			}
 			muts[o] = appended
 			continue
-		}
-
-		if idx, ok := lhs.(*ast.IndexExpr); ok {
-			if ident, ok := idx.X.(*ast.Ident); ok {
+		case *ast.IndexExpr:
+			if ident, ok := lhs.X.(*ast.Ident); ok {
 				t := pass.TypesInfo.TypeOf(ident)
 				if t == nil {
 					continue
@@ -107,6 +122,7 @@ func visitAssign(n *ast.AssignStmt, pass *analysis.Pass) map[types.Object]mutati
 				continue
 			}
 		}
+
 	}
 	return muts
 }

sliceinitiallength/testdata/a.go

@@ -54,3 +54,25 @@ func _() {
 	}
 	fmt.Println(ys)
 }
+
+func _() {
+	xs := []string{"a", "b", "c"}
+	ys := make([]int, len(xs))
+
+	ys = ys[:0]
+	for _, x := range xs {
+		ys = append(ys, len(x))
+	}
+	fmt.Println(ys)
+}
+
+func _() {
+	xs := []string{"a", "b", "c"}
+	ys := make([]int, len(xs))
+
+	ys = append(ys[:0], 0)
+	for _, x := range xs {
+		ys = append(ys, len(x))
+	}
+	fmt.Println(ys)
+}