checkers: fix unlambda panic on variadic func literals (#992)

Fixes #991

Signed-off-by: Iskander Sharipov <[email protected]>

Author: quasilyte

checkers/testdata/unlambda/positive_tests.go

@@ -22,6 +22,36 @@ func functionLiterals() {
 	_ = func(x int, y int) int { return add(x, y) }
 }
 
+func variadicInt(xs ...int) int { return 0 }
+
+func variadicTest() {
+	_ = func(x int) int { return variadicInt(x) }
+	_ = func(x int) int { return variadicInt(x, 1) }
+	_ = func(x, y int) int { return variadicInt(x, y) }
+	_ = func(x, y int) int { return variadicInt(x) }
+
+	/*! replace `func(xs ...int) int { return variadicInt(xs...) }` with `variadicInt` */
+	_ = func(xs ...int) int { return variadicInt(xs...) }
+
+	_ = func(x int, ys ...int) int { return variadicInt(1, 2) }
+	_ = func(x int, y int, _ ...int) int { return variadicInt(x, y) }
+}
+
+func variadicInterfaces(x int, y interface{}, ys ...interface{}) int { return 0 }
+
+func TestSomething() {
+	// See #991
+	_ = func(x int, y interface{}, _ ...interface{}) int {
+		return variadicInterfaces(x, y)
+	}
+	_ = func(x int, y interface{}, _ ...interface{}) int {
+		return variadicInterfaces(x, y, 5, "?")
+	}
+
+	/*! replace `func(x int, y interface{}, zs ...interface{}) int { return variadicInterfaces(x, y, zs...) }` with `variadicInterfaces` */
+	_ = func(x int, y interface{}, zs ...interface{}) int { return variadicInterfaces(x, y, zs...) }
+}
+
 type object struct{}
 
 func (object) returnInt(x int) int { return x }

checkers/unlambda_checker.go

@@ -2,6 +2,7 @@ package checkers
 
 import (
 	"go/ast"
+	"go/token"
 	"go/types"
 
 	"github.com/go-critic/go-critic/checkers/internal/astwalk"
@@ -61,6 +62,14 @@ func (c *unlambdaChecker) VisitExpr(x ast.Expr) {
 	// Now check that all arguments match the parameters.
 	n := 0
 	for _, params := range fn.Type.Params.List {
+		if _, ok := params.Type.(*ast.Ellipsis); ok {
+			if result.Ellipsis == token.NoPos {
+				return
+			}
+			n++
+			continue
+		}
+
 		for _, id := range params.Names {
 			if !astequal.Expr(id, result.Args[n]) {
 				return