feat(strings): add CutLast

gs/strings/godoc.txt

@@ -12,6 +12,7 @@ func ContainsFunc(s string, f func(rune) bool) bool
 func ContainsRune(s string, r rune) bool
 func Count(s, substr string) int
 func Cut(s, sep string) (before, after string, found bool)
+func CutLast(s, sep string) (before, after string, found bool)
 func CutPrefix(s, prefix string) (after string, found bool)
 func CutSuffix(s, suffix string) (before string, found bool)
 func EqualFold(s, t string) bool

gs/strings/parity.json

@@ -29,7 +29,7 @@
     "Cut": {
       "status": "real"
     },
-    "CutLast": { "status": "blocked", "reason": "stdlib function added in a newer toolchain; not implemented by the override" },
+    "CutLast": { "status": "real", "since": "go1.27" },
     "CutPrefix": {
       "status": "real"
     },

gs/strings/strings.test.ts

@@ -10,6 +10,7 @@ import {
   ContainsRune,
   Count,
   Cut,
+  CutLast,
   CutPrefix,
   CutSuffix,
   EqualFold,
@@ -128,6 +129,16 @@ describe('strings', () => {
     })
   })
 
+  describe('CutLast', () => {
+    it('should cut around the last separator', () => {
+      expect(CutLast('a-b-c', '-')).toEqual(['a-b', 'c', true])
+      expect(CutLast('hello', '-')).toEqual(['hello', '', false])
+      expect(CutLast('', '-')).toEqual(['', '', false])
+      expect(CutLast('a--b', '--')).toEqual(['a', 'b', true])
+      expect(CutLast('abc', '')).toEqual(['abc', '', true])
+    })
+  })
+
   describe('CutPrefix', () => {
     it('should cut prefix and report if found', () => {
       expect(CutPrefix('hello world', 'hello ')).toEqual(['world', true])

gs/strings/strings.ts

@@ -662,6 +662,15 @@ export function Cut(s: string, sep: string): [string, string, boolean] {
   return [s.slice(0, index), s.slice(index + sep.length), true]
 }
 
+// CutLast slices s around the last instance of sep, returning the text before and after sep.
+export function CutLast(s: string, sep: string): [string, string, boolean] {
+  const index = s.lastIndexOf(sep)
+  if (index === -1) {
+    return [s, '', false]
+  }
+  return [s.slice(0, index), s.slice(index + sep.length), true]
+}
+
 // CutPrefix returns s without the provided leading prefix string and reports whether it found the prefix.
 export function CutPrefix(s: string, prefix: string): [string, boolean] {
   if (s.startsWith(prefix)) {

tests/tests/strings_cutlast/expected.log

@@ -0,0 +1,4 @@
+CutLast: a/b c true
+Cut: a b/c true
+missing: abc true false
+multi: héllo::wörld end true

tests/tests/strings_cutlast/strings_cutlast.go

@@ -0,0 +1,19 @@
+package main
+
+import "strings"
+
+func main() {
+	// CutLast splits around the last separator, like Cut does around the first.
+	before, after, found := strings.CutLast("a/b/c", "/")
+	println("CutLast:", before, after, found)
+	before, after, found = strings.Cut("a/b/c", "/")
+	println("Cut:", before, after, found)
+
+	// Without the separator, it returns s, "", false.
+	before, after, found = strings.CutLast("abc", "/")
+	println("missing:", before, after == "", found)
+
+	// A multi-byte separator and non-ASCII text cut at the last match.
+	before, after, found = strings.CutLast("héllo::wörld::end", "::")
+	println("multi:", before, after, found)
+}

tests/tests/strings_cutlast/strings_cutlast.gs.ts

@@ -0,0 +1,34 @@
+// Generated file based on strings_cutlast.go
+// Updated when compliance tests are re-run, DO NOT EDIT!
+
+import * as $ from "@goscript/builtin/index.js"
+import * as strings from "@goscript/strings/index.js"
+
+export async function main(): globalThis.Promise<void> {
+	// CutLast splits around the last separator, like Cut does around the first.
+	let [before, after, found] = strings.CutLast("a/b/c", "/")
+	await $.println("CutLast:", before, after, found)
+	let __goscriptTuple0: any = strings.Cut("a/b/c", "/")
+	before = __goscriptTuple0[0]
+	after = __goscriptTuple0[1]
+	found = __goscriptTuple0[2]
+	await $.println("Cut:", before, after, found)
+
+	// Without the separator, it returns s, "", false.
+	let __goscriptTuple1: any = strings.CutLast("abc", "/")
+	before = __goscriptTuple1[0]
+	after = __goscriptTuple1[1]
+	found = __goscriptTuple1[2]
+	await $.println("missing:", before, $.stringEqual(after, ""), found)
+
+	// A multi-byte separator and non-ASCII text cut at the last match.
+	let __goscriptTuple2: any = strings.CutLast("h\xc3\xa9llo::w\xc3\xb6rld::end", "::")
+	before = __goscriptTuple2[0]
+	after = __goscriptTuple2[1]
+	found = __goscriptTuple2[2]
+	await $.println("multi:", before, after, found)
+}
+
+if ($.isMainScript(import.meta)) {
+	await main()
+}

tests/tests/strings_cutlast/tsconfig.json

@@ -0,0 +1,25 @@
+{
+  "compilerOptions": {
+    "paths": {
+      "*": [
+        "./*"
+      ],
+      "@go/github.com/s4wave/goscript/*": [
+        "../../../*"
+      ],
+      "@goscript/*": [
+        "../../../tests/tests/strings_cutlast/run/output/@goscript/*",
+        "../../../gs/*",
+        "../../../tests/deps/*"
+      ],
+      "@goscript/github.com/s4wave/goscript/tests/tests/strings_cutlast/*": [
+        "./*"
+      ]
+    }
+  },
+  "extends": "../../../tests/tsconfig.base.json",
+  "include": [
+    "index.ts",
+    "strings_cutlast.gs.ts"
+  ]
+}