chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/command/split.go

@@ -8,13 +8,6 @@ import (
 	"unicode/utf8"
 )
 
-var (
-	errCommandEmpty            = errors.New("command is empty")
-	errSingleQuoteUnterminated = errors.New("unterminated single-quoted string")
-	errDoubleQuoteUnterminated = errors.New("unterminated double-quoted string")
-	errEscapeUnterminated      = errors.New("unterminated backslash-escape")
-)
-
 // split splits a command string into a slice of arguments.
 // This is especially important for commands such as:
 // /bin/sh -c "echo hello"
@@ -25,7 +18,7 @@ var (
 // - expansion (brace, shell or pathname).
 func split(command string) (words []string, err error) {
 	if command == "" {
-		return nil, fmt.Errorf("%w", errCommandEmpty)
+		return nil, errors.New("command is empty")
 	}
 
 	const bufferSize = 1024
@@ -42,7 +35,7 @@ func split(command string) (words []string, err error) {
 		case character == '\\':
 			// Look ahead to eventually skip an escaped newline
 			if command[startIndex+runeSize:] == "" {
-				return nil, fmt.Errorf("%w: %q", errEscapeUnterminated, command)
+				return nil, fmt.Errorf("unterminated backslash-escape: %q", command)
 			}
 			character, runeSize := utf8.DecodeRuneInString(command[startIndex+runeSize:])
 			if character == '\n' {
@@ -119,7 +112,7 @@ func handleDoubleQuoted(input string, startIndex int, buffer *bytes.Buffer) (
 			startIndex = cursor
 		}
 	}
-	return "", 0, fmt.Errorf("%w", errDoubleQuoteUnterminated)
+	return "", 0, errors.New("unterminated double-quoted string")
 }
 
 func handleSingleQuoted(input string, startIndex int, buffer *bytes.Buffer) (
@@ -127,7 +120,7 @@ func handleSingleQuoted(input string, startIndex int, buffer *bytes.Buffer) (
 ) {
 	closingQuoteIndex := strings.IndexRune(input[startIndex:], '\'')
 	if closingQuoteIndex == -1 {
-		return "", 0, fmt.Errorf("%w", errSingleQuoteUnterminated)
+		return "", 0, errors.New("unterminated single-quoted string")
 	}
 	buffer.WriteString(input[startIndex : startIndex+closingQuoteIndex])
 	const singleQuoteRuneLength = 1
@@ -139,7 +132,7 @@ func handleEscaped(input string, startIndex int, buffer *bytes.Buffer) (
 	word string, newStartIndex int, err error,
 ) {
 	if input[startIndex:] == "" {
-		return "", 0, fmt.Errorf("%w", errEscapeUnterminated)
+		return "", 0, errors.New("unterminated backslash-escape")
 	}
 	character, runeLength := utf8.DecodeRuneInString(input[startIndex:])
 	if character != '\n' { // backslash-escaped newline is ignored

internal/command/split_test.go

@@ -12,12 +12,10 @@ func Test_split(t *testing.T) {
 	testCases := map[string]struct {
 		command    string
 		words      []string
-		errWrapped error
 		errMessage string
 	}{
 		"empty": {
 			command:    "",
-			errWrapped: errCommandEmpty,
 			errMessage: "command is empty",
 		},
 		"concrete_sh_command": {
@@ -74,22 +72,18 @@ func Test_split(t *testing.T) {
 		},
 		"unterminated_single_quote": {
 			command:    "'abc'\\''def",
-			errWrapped: errSingleQuoteUnterminated,
 			errMessage: `splitting word in "'abc'\\''def": unterminated single-quoted string`,
 		},
 		"unterminated_double_quote": {
 			command:    "\"abc'def",
-			errWrapped: errDoubleQuoteUnterminated,
 			errMessage: `splitting word in "\"abc'def": unterminated double-quoted string`,
 		},
 		"unterminated_escape": {
 			command:    "abc\\",
-			errWrapped: errEscapeUnterminated,
 			errMessage: `splitting word in "abc\\": unterminated backslash-escape`,
 		},
 		"unterminated_escape_only": {
 			command:    "   \\",
-			errWrapped: errEscapeUnterminated,
 			errMessage: `unterminated backslash-escape: "   \\"`,
 		},
 	}
@@ -101,9 +95,10 @@ func Test_split(t *testing.T) {
 			words, err := split(testCase.command)
 
 			assert.Equal(t, testCase.words, words)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
-				assert.EqualError(t, err, testCase.errMessage)
+			if testCase.errMessage != "" {
+				assert.ErrorContains(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}