lib/strings+test: port join from Hare str... variadic (#19)

lib/strings/strings.ww

@@ -129,6 +129,47 @@ export fn concat(strs: str...) str = {
 	return r;
 };
 
+// join — fresh allocation with `delim` placed between each element of
+// `strs`. Caller releases with `os.free(r.ptr, r.len: u64)`.
+// ref/hare/strings/concat.ha:46. Hare's `nomem` return is dropped:
+// `os.alloc` aborts on OOM.
+export fn join(delim: str, strs: str...) str = {
+	let total: i32 = 0;
+	let i: i32 = 0;
+	for (i < strs.len) {
+		total += strs[i].len;
+		if (i + 1 < strs.len) { total += delim.len; };
+		i += 1;
+	};
+	let r: str;
+	r.ptr = nil;
+	r.len = 0;
+	if (total == 0) { return r; };
+	let buf: *u8 = os.alloc(total: u64): *u8;
+	let off: i32 = 0;
+	i = 0;
+	for (i < strs.len) {
+		let j: i32 = 0;
+		for (j < strs[i].len) {
+			buf[off + j] = strs[i][j];
+			j += 1;
+		};
+		off += strs[i].len;
+		if (i + 1 < strs.len) {
+			j = 0;
+			for (j < delim.len) {
+				buf[off + j] = delim[j];
+				j += 1;
+			};
+			off += delim.len;
+		};
+		i += 1;
+	};
+	r.ptr = buf;
+	r.len = total;
+	return r;
+};
+
 // sub — borrowed `s[start..end]`. ref/hare/strings/sub.ha:30 is
 // rune-wise; this ww form is byte-wise (no rune iterator yet, planned
 // for commit 2). Clamps out-of-range silently where Hare aborts —

lib/strings/stringstest.ww

@@ -99,6 +99,62 @@ fn streq(a: str, b: str) bool = {
 	};
 };
 
+// ---- join -------------------------------------------------------------
+// ref/hare/strings/concat.ha:64. Rows mirror Hare's @test fn join
+// (0-arg, 1-arg, empty-sep, 3-arg.) plus 2-arg, all-empties, long sep,
+// multibyte, empty-mid (delim still inserted around the empty slot).
+// Per-row `signalled` 1620+i narrows the failing row.
+
+@test fn join_cases() void = {
+	let pool: [19]str;
+	pool[0]  = "hello";
+	pool[1]  = "a";
+	pool[2]  = "b";
+	pool[3]  = "a";
+	pool[4]  = "b";
+	pool[5]  = "c";
+	pool[6]  = "a";
+	pool[7]  = "b";
+	pool[8]  = "c";
+	pool[9]  = "";
+	pool[10] = "";
+	pool[11] = "a";
+	pool[12] = "b";
+	pool[13] = "c";
+	pool[14] = "こん";
+	pool[15] = "にちは";
+	pool[16] = "a";
+	pool[17] = "";
+	pool[18] = "b";
+
+	let argo:   [9]i32;
+	let argn:   [9]i32;
+	let seps:   [9]str;
+	let want:   [9]str;
+	argo[0]=0;  argn[0]=0; seps[0]=".";    want[0]="";
+	argo[1]=0;  argn[1]=1; seps[1]=".";    want[1]="hello";
+	argo[2]=1;  argn[2]=2; seps[2]=", ";   want[2]="a, b";
+	argo[3]=3;  argn[3]=3; seps[3]=".";    want[3]="a.b.c";
+	argo[4]=6;  argn[4]=3; seps[4]="";     want[4]="abc";
+	argo[5]=9;  argn[5]=2; seps[5]=",";    want[5]=",";
+	argo[6]=11; argn[6]=3; seps[6]=" :: "; want[6]="a :: b :: c";
+	argo[7]=14; argn[7]=2; seps[7]="・";   want[7]="こん・にちは";
+	argo[8]=16; argn[8]=3; seps[8]="-";    want[8]="a--b";
+
+	let i: i32 = 0;
+	for (i < 9) {
+		signalled = 1620 + i;
+		let argv: []str;
+		argv.ptr = &pool[argo[i]];
+		argv.len = argn[i];
+		argv.cap = argn[i];
+		let got: str = strings.join(seps[i], argv...);
+		if (!streq(got, want[i])) { fail(); };
+		if (got.len > 0) { os.free(got.ptr: *void, got.len: u64); };
+		i += 1;
+	};
+};
+
 // ---- hasprefix --------------------------------------------------------
 // ref/hare/strings/suffix.ha:18.
 
@@ -842,6 +898,7 @@ fn streq(a: str, b: str) bool = {
 export fn main() i32 = {
 	signalled = 1;  dup_cases();
 	signalled = 2;  concat_cases();
+	signalled = 30; join_cases();
 	signalled = 3;  hasprefix_cases();
 	signalled = 4;  hassuffix_cases();
 	signalled = 5;  contains_cases();