add crstrings library

crstrings/utils.go

@@ -0,0 +1,99 @@
+// Copyright 2024 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package crstrings
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+)
+
+// JoinStringers concatenates the string representations of the given
+// fmt.Stringer implementations.
+func JoinStringers[T fmt.Stringer](delim string, args ...T) string {
+	switch len(args) {
+	case 0:
+		return ""
+	case 1:
+		return args[0].String()
+	}
+	elems := make([]string, len(args))
+	for i := range args {
+		elems[i] = args[i].String()
+	}
+	return strings.Join(elems, delim)
+}
+
+// MapAndJoin converts each argument to a string using the given function and
+// joins the strings with the given delimiter.
+func MapAndJoin[T any](fn func(T) string, delim string, args ...T) string {
+	switch len(args) {
+	case 0:
+		return ""
+	case 1:
+		return fn(args[0])
+	}
+	elems := make([]string, len(args))
+	for i := range args {
+		elems[i] = fn(args[i])
+	}
+	return strings.Join(elems, delim)
+}
+
+// If returns the given value if the flag is true, otherwise an empty string.
+func If(flag bool, trueValue string) string {
+	return IfElse(flag, trueValue, "")
+}
+
+// IfElse returns the value that matches the value of the flag.
+func IfElse(flag bool, trueValue, falseValue string) string {
+	if flag {
+		return trueValue
+	}
+	return falseValue
+}
+
+// WithSep prints the strings a and b with the given separator in-between,
+// unless one of the strings is empty (in which case the other string is
+// returned).
+func WithSep(a string, separator string, b string) string {
+	if a == "" {
+		return b
+	}
+	if b == "" {
+		return a
+	}
+	return strings.Join([]string{a, b}, separator)
+}
+
+// FilterEmpty removes empty strings from the given slice.
+func FilterEmpty(elems []string) []string {
+	return slices.DeleteFunc(elems, func(s string) bool {
+		return s == ""
+	})
+}
+
+// Lines breaks up the given string into lines.
+func Lines(s string) []string {
+	// Remove any trailing newline (to avoid getting an extraneous empty line at
+	// the end).
+	s = strings.TrimSuffix(s, "\n")
+	if s == "" {
+		// In this case, Split returns a slice with a single empty string (which is
+		// not what we want).
+		return nil
+	}
+	return strings.Split(s, "\n")
+}

crstrings/utils_test.go

@@ -0,0 +1,83 @@
+// Copyright 2024 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package crstrings
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+type num int
+
+func (n num) String() string {
+	return fmt.Sprintf("%03d", int(n))
+}
+
+func TestJoinStringers(t *testing.T) {
+	nums := []num{0, 1, 2, 3}
+	expect(t, "", JoinStringers(", ", nums[:0]...))
+	expect(t, "000", JoinStringers(", ", nums[0]))
+	expect(t, "000, 001", JoinStringers(", ", nums[0], nums[1]))
+	expect(t, "000, 001, 002, 003", JoinStringers(", ", nums...))
+}
+
+func TestMapAndJoin(t *testing.T) {
+	nums := []int{0, 1, 2, 3}
+	fn := func(n int) string {
+		return fmt.Sprintf("%d", n)
+	}
+	expect(t, "", MapAndJoin(fn, ", ", nums[:0]...))
+	expect(t, "0", MapAndJoin(fn, ", ", nums[0]))
+	expect(t, "0, 1", MapAndJoin(fn, ", ", nums[0], nums[1]))
+	expect(t, "0, 1, 2, 3", MapAndJoin(fn, ", ", nums...))
+}
+
+func expect(t *testing.T, expected, actual string) {
+	t.Helper()
+	if actual != expected {
+		t.Errorf("expected %q got %q", expected, actual)
+	}
+}
+
+func TestIf(t *testing.T) {
+	expect(t, "", If(false, "true"))
+	expect(t, "true", If(true, "true"))
+}
+
+func TestIfElse(t *testing.T) {
+	expect(t, "false", IfElse(false, "true", "false"))
+	expect(t, "true", IfElse(true, "true", "false"))
+}
+
+func TestWithSep(t *testing.T) {
+	expect(t, "a,b", WithSep("a", ",", "b"))
+	expect(t, "a", WithSep("a", ",", ""))
+	expect(t, "b", WithSep("", ",", "b"))
+}
+
+func TestFilterEmpty(t *testing.T) {
+	s := []string{"a", "", "b", "", "c", ""}
+	expect(t, "a,b,c", strings.Join(FilterEmpty(s), ","))
+}
+
+func TestLines(t *testing.T) {
+	expect(t, `["a" "b" "c"]`, fmt.Sprintf("%q", Lines("a\nb\nc")))
+	expect(t, `["a" "b" "c"]`, fmt.Sprintf("%q", Lines("a\nb\nc\n")))
+	expect(t, `["a" "b" "c" ""]`, fmt.Sprintf("%q", Lines("a\nb\nc\n\n")))
+	expect(t, `["" "a" "b" "c"]`, fmt.Sprintf("%q", Lines("\na\nb\nc\n")))
+	expect(t, `[]`, fmt.Sprintf("%q", Lines("")))
+	expect(t, `[]`, fmt.Sprintf("%q", Lines("\n")))
+}