[PATCH] let bychunk() read the last element; guard for negative sz

["S. Gilles" <sgilles@xxxxxxxxxxxx>]

I mentioned on IRC that bychunk() was skipping the last element of
a slice, here's a fix for that, as well as some redundant tests and
some probably unneeded input validation. I don't have any strong
feelings about protecting someone from shooting themselves in the
foot with bychunk([1][:], -100), but it's easier to remove in review
than to add later.

---
 lib/iter/chunk.myr      |  4 ++--
 lib/iter/test/chunk.myr | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 lib/iter/test/chunk.myr

diff --git a/lib/iter/chunk.myr b/lib/iter/chunk.myr
index 5d0d68cc..80a74e63 100644
--- a/lib/iter/chunk.myr
+++ b/lib/iter/chunk.myr
@@ -12,7 +12,7 @@ pkg iter =
 ;;
 
 generic bychunk = {a, sz
-	-> [.sl = a, .idx = 0, .blksz = sz]
+	-> [.sl = a, .idx = 0, .blksz = std.max(sz, 1)]
 }
 
 impl iterable chunkiter(@a) -> @a[:] =
@@ -20,7 +20,7 @@ impl iterable chunkiter(@a) -> @a[:] =
 		var len
 
 		len = std.min(itp.blksz, itp.sl.len - itp.idx)
-		if itp.idx + len == itp.sl.len
+		if itp.idx + len > itp.sl.len || itp.idx >= itp.sl.len
 			-> false
 		;;
 		valp# = itp.sl[itp.idx: itp.idx + len]
diff --git a/lib/iter/test/chunk.myr b/lib/iter/test/chunk.myr
new file mode 100644
index 00000000..cd1498f9
--- /dev/null
+++ b/lib/iter/test/chunk.myr
@@ -0,0 +1,44 @@
+use std
+use testr
+
+use iter
+
+const main = {
+	testr.run([
+		[.name = "bychunk-01", .fn = bychunk01],
+		[.name = "bychunk-02", .fn = bychunk02],
+		[.name = "bychunk-03", .fn = bychunk03],
+		[.name = "bychunk-04", .fn = bychunk04],
+		[.name = "bychunk-05", .fn = bychunk05],
+	][:])
+}
+
+const verify_bychunk = {c, v, n, e
+	var sb : std.strbuf# = std.mksb()
+	std.sbfmt(sb, " ")
+	for w : iter.bychunk(v, n)
+		std.sbfmt(sb, "{} ", w)
+	;;
+	var a : byte[:] = std.sbfin(sb)
+	testr.check(c, std.eq(e, a), "expected “{}”, got “{}”", e, a)
+}
+
+const bychunk01 = {c
+	verify_bychunk(c, [1, 2, 3, 4][:], 1, " [1] [2] [3] [4] ")
+}
+
+const bychunk02 = {c
+	verify_bychunk(c, [1, 2, 3, 4, 5, 6, 7, 8][:], 3, " [1, 2, 3] [4, 5, 6] [7, 8] ")
+}
+
+const bychunk03 = {c
+	verify_bychunk(c, [1, 2, 3, 4][:], 99, " [1, 2, 3, 4] ")
+}
+
+const bychunk04 = {c
+	verify_bychunk(c, [1, 2, 3, 4][:], -2, " [1] [2] [3] [4] ")
+}
+
+const bychunk05 = {c
+	verify_bychunk(c, [][:], 3, " ")
+}
-- 
2.15.1