ireturn: update tests & docs (#3800)

Author: butuzov

.golangci.reference.yml

@@ -1159,13 +1159,14 @@ linters-settings:
     max: 5
 
   ireturn:
-    # ireturn allows using `allow` and `reject` settings at the same time.
+    # ireturn does not allow using `allow` and `reject` settings at the same time.
     # Both settings are lists of the keywords and regular expressions matched to interface or package names.
     # keywords:
     # - `empty` for `interface{}`
     # - `error` for errors
     # - `stdlib` for standard library
     # - `anon` for anonymous interfaces
+    # - `generic` for generic interfaces added in go 1.18
 
     # By default, it allows using errors, empty interfaces, anonymous interfaces,
     # and interfaces provided by the standard library.

test/testdata/configs/ireturn_reject_generics.yml

@@ -0,0 +1,4 @@
+linters-settings:
+  ireturn:
+    reject:
+    - generic

test/testdata/configs/ireturn_stdlib_reject.yml renamed to test/testdata/configs/ireturn_reject_stdlib.yml

@@ -0,0 +1,25 @@
+//golangcitest:args -Eireturn
+//golangcitest:config_path testdata/configs/ireturn_reject_generics.yml
+package testdata
+
+import (
+	"bytes"
+	"io"
+)
+
+func NewWriter() io.Writer {
+	var buf bytes.Buffer
+	return &buf
+}
+
+func TestError() error {
+	return nil
+}
+
+func Get[K comparable, V int64 | float64](m map[K]V) V { // want `Get returns generic interface \(V\)`
+	var s V
+	for _, v := range m {
+		s += v
+	}
+	return s
+}

test/testdata/ireturn_reject_generics.go

@@ -1,5 +1,5 @@
 //golangcitest:args -Eireturn
-//golangcitest:config_path testdata/configs/ireturn_stdlib_reject.yml
+//golangcitest:config_path testdata/configs/ireturn_reject_stdlib.yml
 package testdata
 
 import (