constant-logical-expr (new rule) (#55)

* suspicious-logical-expr (new rule)

* renames 'suspicious-logical-expression' to 'constant-logical-expression'

README.md

@@ -265,6 +265,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | `unnecessary-stmt`    |  n/a   | Suggests removing or simplifying unnecessary statements          |    no    |  no   |
 | `struct-tag`          |  n/a   | Checks common struct tags like `json`,`xml`,`yaml`               |    no    |  no   |
 | `modifies-value-receiver` |  n/a   | Warns on assignments to value-passed method receivers        |    no    |  yes  |
+| `constant-logical-expr`   |  n/a   | Warns on constant logical expressions                        |    no    |  no   |
 | `bool-literal-in-expr`|  n/a   | Suggests removing Boolean literals from logic expressions        |    no    |  no   |
 
 ## Available Formatters

config.go

@@ -61,6 +61,7 @@ var allRules = append([]lint.Rule{
 	&rule.UnnecessaryStmtRule{},
 	&rule.StructTagRule{},
 	&rule.ModifiesValRecRule{},
+	&rule.ConstantLogicalExprRule{},
 	&rule.BoolLiteralRule{},
 }, defaultRules...)
 

fixtures/constant-logical-expr.go

@@ -0,0 +1,26 @@
+package fixtures
+
+// from github.com/ugorji/go/codec/helper.go
+func isNaN(f float64) bool { return f != f } // MATCH /expression always evaluates to false/
+
+func skip(f float64) bool { return f != g }
+
+func foo1(f float64) bool { return foo2(2.) > foo2(2.) } // MATCH /expression always evaluates to false/
+
+func foo2(f float64) bool { return f < f } // MATCH /expression always evaluates to false/
+
+func foo3(f float64) bool { return f <= f } // MATCH /expression always evaluates to false/
+
+func foo4(f float64) bool { return f >= f } // MATCH /expression always evaluates to false/
+
+func foo5(f float64) bool { return f == f } // MATCH /expression always evaluates to true/
+
+func foo6(f float64) bool { return fmt.Sprintf("%s", buf1.Bytes()) == fmt.Sprintf("%s", buf1.Bytes()) } // MATCH /expression always evaluates to true/
+
+func foo7(f float64) bool {
+	return fFoo(fBar(isNaN(10.), bpar), 10000) || fFoo(fBar(isNaN(10.), bpar), 10000) // MATCH /left and right hand-side sub-expressions are the same/
+}
+
+func foo8(f float64) bool {
+	return fFoo(fBar(isNaN(10.), bpar), 10000) && fFoo(fBar(isNaN(10.), bpar), 10000) // MATCH /left and right hand-side sub-expressions are the same/
+}

rule/constant-logical-expr.go

@@ -0,0 +1,106 @@
+package rule
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/mgechev/revive/lint"
+	"go/ast"
+	"go/format"
+	"go/token"
+)
+
+// ConstantLogicalExprRule warns on constant logical expressions.
+type ConstantLogicalExprRule struct{}
+
+// Apply applies the rule to given file.
+func (r *ConstantLogicalExprRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	onFailure := func(failure lint.Failure) {
+		failures = append(failures, failure)
+	}
+
+	astFile := file.AST
+	w := &lintConstantLogicalExpr{astFile, onFailure}
+	ast.Walk(w, astFile)
+	return failures
+}
+
+// Name returns the rule name.
+func (r *ConstantLogicalExprRule) Name() string {
+	return "constant-logical-expr"
+}
+
+type lintConstantLogicalExpr struct {
+	file      *ast.File
+	onFailure func(lint.Failure)
+}
+
+func (w *lintConstantLogicalExpr) Visit(node ast.Node) ast.Visitor {
+	switch n := node.(type) {
+	case *ast.BinaryExpr:
+		if !w.isOperatorWithLogicalResult(n.Op) {
+			return w
+		}
+
+		if !w.areEqual(n.X, n.Y) {
+			return w
+		}
+
+		if n.Op == token.EQL {
+			w.newFailure(n, "expression always evaluates to true")
+			return w
+		}
+
+		if w.isInequalityOperator(n.Op) {
+			w.newFailure(n, "expression always evaluates to false")
+			return w
+		}
+
+		w.newFailure(n, "left and right hand-side sub-expressions are the same")
+	}
+
+	return w
+}
+
+func (w *lintConstantLogicalExpr) isOperatorWithLogicalResult(t token.Token) bool {
+	switch t {
+	case token.LAND, token.LOR, token.EQL, token.LSS, token.GTR, token.NEQ, token.LEQ, token.GEQ:
+		return true
+	}
+
+	return false
+}
+
+func (w *lintConstantLogicalExpr) isInequalityOperator(t token.Token) bool {
+	switch t {
+	case token.LSS, token.GTR, token.NEQ, token.LEQ, token.GEQ:
+		return true
+	}
+
+	return false
+}
+
+func (w lintConstantLogicalExpr) areEqual(x, y ast.Expr) bool {
+	fset := token.NewFileSet()
+	var buf1 bytes.Buffer
+	if err := format.Node(&buf1, fset, x); err != nil {
+		return false // keep going in case of error
+	}
+
+	var buf2 bytes.Buffer
+	if err := format.Node(&buf2, fset, y); err != nil {
+		return false // keep going in case of error
+	}
+
+	return fmt.Sprintf("%s", buf1.Bytes()) == fmt.Sprintf("%s", buf2.Bytes())
+}
+
+func (w lintConstantLogicalExpr) newFailure(node ast.Node, msg string) {
+	w.onFailure(lint.Failure{
+		Confidence: 1,
+		Node:       node,
+		Category:   "logic",
+		Failure:    msg,
+	})
+}

test/constant-logical-expr_test.go

@@ -0,0 +1,12 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/rule"
+)
+
+// ConstantLogicalExpr rule.
+func TestConstantLogicalExpr(t *testing.T) {
+	testRule(t, "constant-logical-expr", &rule.ConstantLogicalExprRule{})
+}