do not shadow existing errors

noinlineerr.go

@@ -63,9 +63,11 @@ func inlineErrorInspector(pass *analysis.Pass) func(n ast.Node) {
 				continue
 			}
 
-			if len(assignStmt.Lhs) != 1 {
-				// if there are more than 1 assignment then we can make a shadow conflict with other variables
-				// so don't do anything beside simple error message
+			// if there are more than 1 assignment
+			// or there are any variables with same name
+			// then we can make a shadow conflict with other variables
+			// so don't do anything beside simple error message
+			if len(assignStmt.Lhs) != 1 || shadowVarsExists(ident.Name, pass.TypesInfo.Scopes[ifStmt]) {
 				pass.Reportf(ident.Pos(), errMessage)
 				return
 			}
@@ -75,6 +77,7 @@ func inlineErrorInspector(pass *analysis.Pass) func(n ast.Node) {
 			// and we can autofix that
 
 			var buf bytes.Buffer
+
 			_ = printer.Fprint(&buf, pass.Fset, assignStmt)
 			assignText := buf.String()
 
@@ -116,3 +119,16 @@ func isError(obj types.Object) bool {
 
 	return types.AssignableTo(obj.Type(), errorType)
 }
+
+func shadowVarsExists(name string, scope *types.Scope) bool {
+	if scope == nil {
+		return false
+	}
+
+	parentScope := scope.Parent()
+	if parentScope == nil {
+		return false
+	}
+
+	return parentScope.Lookup(name) != nil
+}

testdata/src/a/main.go

@@ -7,7 +7,7 @@ import (
 
 type MyAliasErr error
 
-type MyCustomError struct {}
+type MyCustomError struct{}
 
 func (mc *MyCustomError) Error() string {
 	return "error"
@@ -84,3 +84,22 @@ func invalid() error {
 
 	return nil
 }
+
+func errShadow() error {
+	var err error
+	if err := doSomething(); err != nil { // want "avoid inline error handling using `if err := ...; err != nil`; use plain assignment `err := ...`"
+		return err
+	}
+	fmt.Println(err)
+
+	return nil
+}
+
+func naming() error {
+	if otherName := doSomething(); otherName != nil { // want "avoid inline error handling using `if err := ...; err != nil`; use plain assignment `err := ...`"
+		return otherName
+	}
+
+	return nil
+}
+

testdata/src/a/main.go.golden

@@ -8,7 +8,7 @@ import (
 
 type MyAliasErr error
 
-type MyCustomError struct {}
+type MyCustomError struct{}
 
 func (mc *MyCustomError) Error() string {
 	return "error"
@@ -86,6 +86,25 @@ func invalid() error {
     if err != nil { // want "avoid inline error handling using `if err := ...; err != nil`; use plain assignment `err := ...`"
 		return err
 	}
+
+    return nil
+}
+
+func errShadow() error {
+	var err error
+	if err := doSomething(); err != nil { // want "avoid inline error handling using `if err := ...; err != nil`; use plain assignment `err := ...`"
+		return err
+	}
+	fmt.Println(err)
+
+	return nil
+}
+
+func naming() error {
+    otherName := doSomething()
+    if otherName != nil { // want "avoid inline error handling using `if err := ...; err != nil`; use plain assignment `err := ...`"
+        return otherName
+    }
 
     return nil
 }