New rule: modifies-parameter (#25)

* Adds rule superfluous-else (an extension of indent-error-flow)

* Fix superfluous-else rule struct namming.

* Adds superfuous-else rule to the rules table

* Adds confusing-naming rule

* adds multifile test

* clean-up

* fix config.go

* working version

rule/modifies-param.go

@@ -0,0 +1,94 @@
+package rule
+
+import (
+	"fmt"
+	"go/ast"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// ModifiesParamRule lints given else constructs.
+type ModifiesParamRule struct{}
+
+// Apply applies the rule to given file.
+func (r *ModifiesParamRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	onFailure := func(failure lint.Failure) {
+		failures = append(failures, failure)
+	}
+
+	w := lintModifiesParamRule{onFailure: onFailure}
+	ast.Walk(w, file.AST)
+	return failures
+}
+
+// Name returns the rule name.
+func (r *ModifiesParamRule) Name() string {
+	return "modifies-parameter"
+}
+
+type lintModifiesParamRule struct {
+	params    map[string]bool
+	onFailure func(lint.Failure)
+}
+
+func retrieveParamNames(pl []*ast.Field) map[string]bool {
+	result := make(map[string]bool, len(pl))
+	for _, p := range pl {
+		for _, n := range p.Names {
+			result[n.Name] = true
+		}
+	}
+	return result
+}
+
+func checkAssign(lhs []ast.Expr, w lintModifiesParamRule) {
+	for _, e := range lhs {
+		id, ok := e.(*ast.Ident)
+		if ok {
+			if w.params[id.Name] {
+				w.onFailure(lint.Failure{
+					Confidence: 0.5,
+					Node:       id,
+					Category:   "bad practice",
+					URL:        "#modifies-parameter",
+					Failure:    fmt.Sprintf("parameter '%s' seems to be a modified", id.Name),
+				})
+			}
+		}
+	}
+}
+
+func (w lintModifiesParamRule) Visit(node ast.Node) ast.Visitor {
+	switch v := node.(type) {
+	case *ast.FuncDecl:
+		w.params = retrieveParamNames(v.Type.Params.List)
+	case *ast.IncDecStmt:
+		if id, ok := v.X.(*ast.Ident); ok {
+			checkParam(id, &w)
+		}
+	case *ast.AssignStmt:
+		lhs := v.Lhs
+		for _, e := range lhs {
+			id, ok := e.(*ast.Ident)
+			if ok {
+				checkParam(id, &w)
+			}
+		}
+	}
+
+	return w
+}
+
+func checkParam(id *ast.Ident, w *lintModifiesParamRule) {
+	if w.params[id.Name] {
+		w.onFailure(lint.Failure{
+			Confidence: 0.5, // confidence is low because of shadow variables
+			Node:       id,
+			Category:   "bad practice",
+			URL:        "#modifies-parameter",
+			Failure:    fmt.Sprintf("parameter '%s' seems to be modified", id),
+		})
+	}
+}