Add some additional linters (#250)

Both of these catch bugs, not style

Author: sethvargo

.golangci.yml

@@ -67,7 +67,9 @@ linters:
     - 'ineffassign'
     - 'loggercheck'
     - 'makezero'
+    - 'mirror'
     - 'misspell'
+    - 'nilerr'
     - 'noctx'
     - 'nolintlint'
     - 'nosprintfhostport'

cli/flags_test.go

@@ -531,7 +531,7 @@ func ExampleFlagSet_AfterParse_checkIfError() {
 		// Do not run this function if flag parsing or other AfterParse functions
 		// have failed.
 		if existingErr != nil {
-			return nil
+			return nil //nolint:nilerr
 		}
 
 		// Logic

renderer/funcs.go

@@ -125,7 +125,7 @@ func toStringSlice(i any) ([]string, error) {
 func joinStrings(i any, sep string) (string, error) {
 	l, err := toStringSlice(i)
 	if err != nil {
-		return "", nil
+		return "", err
 	}
 	return strings.Join(l, sep), nil
 }
@@ -134,7 +134,7 @@ func joinStrings(i any, sep string) (string, error) {
 func toSentence(i any, joiner string) (string, error) {
 	l, err := toStringSlice(i)
 	if err != nil {
-		return "", nil
+		return "", err
 	}
 
 	switch len(l) {