rules.go: add exprUnparen rule

Refs go-critic/go-critic#836

Signed-off-by: Iskander Sharipov <quasilyte@gmail.com>

analyzer/testdata/src/extra/file.go

@@ -329,3 +329,16 @@ func testYodaExpr() {
 	if nil != clusterContext.PostInstallData.AnotherNestedStruct.DeeplyNestedField { // want `\Qsuggestion: $s != nil`
 	}
 }
+
+func superfluousParens() {
+	f := func(xs ...interface{}) int { return 0 }
+	xs := []int{1, 2}
+
+	f(0)
+	f((1))                   // want `\Qthe parentheses around 1 are superfluous`
+	f((xs[0] + 2))           // want `\Qthe parentheses around xs[0] + 2 are superfluous`
+	f(0, (1 + 2))            // want `\Qthe parentheses around 1 + 2 are superfluous`
+	f(0, 1, (xs[0] + xs[1])) // want `\Qthe parentheses around xs[0] + xs[1] are superfluous`
+	f(0, (f(0)), 0)          // want `\Qthe parentheses around f(0) are superfluous`
+	f((0), (1))              // want `\Qthe parentheses around 0 are superfluous`
+}

analyzer/testdata/src/extra/rules.go

@@ -37,6 +37,9 @@ func _(m fluent.Matcher) {
 	// that ||, the result would not be functionally identical.
 	m.Match(`($a) || ($b)`).Report(`rewrite as '$a || $b'`)
 	m.Match(`($a) && ($b)`).Report(`rewrite as '$a && $b'`)
+	m.Match(`$f($*_, ($x), $*_)`).
+		Report(`the parentheses around $x are superfluous`).
+		Suggest(`$f($x)`)
 
 	m.Match(`context.TODO()`).Report(`might want to replace context.TODO()`)
 

rules.go

@@ -90,6 +90,12 @@ func _(m fluent.Matcher) {
 		Suggest(`$a+$b`)
 }
 
+func exprUnparen(m fluent.Matcher) {
+	m.Match(`$f($*_, ($x), $*_)`).
+		Report(`the parentheses around $x are superfluous`).
+		Suggest(`$f($x)`)
+}
+
 func osFilepath(m fluent.Matcher) {
 	// path/filepath package forwards path separators so if
 	// the file already uses filepath-related API it might be