Bug 19042 – Chunking a padRight'ed range leads to range violations

The following code exhibits a range violation: import std.stdio; import std.range; import std.conv; void main() { pragma(msg, [2,5,13].padRight(42, 10).chunks(5).to!string); } Compiler output: /dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(12811): Error: slice [5..3] exceeds array bounds [0..3] /dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(12811): called from here: Result(null, 0, 0LU, 0LU, 0LU).this(b <= this.data.length ? this.data[a..b] : this.data[a..this.data.length], this.element, b - a) /dlang/dmd/linux/bin64/../../src/phobos/std/range/primitives.d(1743): called from here: r.opSlice(n, __dollar) /dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(7704): called from here: popFrontN(this._source, this._chunkSize) /dlang/dmd/linux/bin64/../../src/phobos/std/format.d(3299): called from here: val.popFront() /dlang/dmd/linux/bin64/../../src/phobos/std/format.d(4127): called from here: formatRange(w, val, f) /dlang/dmd/linux/bin64/../../src/phobos/std/format.d(1845): called from here: formatValueImpl(w, val, f) /dlang/dmd/linux/bin64/../../src/phobos/std/conv.d(151): called from here: formatValue(w, src, f) /dlang/dmd/linux/bin64/../../src/phobos/std/conv.d(1018): called from here: toStr(value) /dlang/dmd/linux/bin64/../../src/phobos/std/conv.d(222): called from here: toImpl(_param_0) onlineapp.d(7): called from here: to(chunks(padRight([2, 5, 13], 42, 10LU), 5LU)) onlineapp.d(7): while evaluating pragma(msg, chunks(padRight([2, 5, 13], 42, 10LU), 5LU).to!string) The problem occurs almost indepentently from the supplied arguments and is not restricted to compile-time evaluation, the only requirement that I could determine is that padRight needs to extend its input by at least one element. Replacing chunks with evenChunks results in the same error. padLeft does not appear to be affected by this issue. It can be reproduced in all versions since the introduction of padRight (2.072).

This bug is triggered when a slice is taken entirely from the pad section at the end of the range. Here's another variation: ---- issue_19042.d ---- import std.range; import std.stdio; void main(string[] args) { auto r = [1, 2, 3, 4].padRight(0, 10); writeln("r[7 .. 9] : ", r[7 .. 9]); } ---- Run ------- $ dmd issue_19042.d $ ./issue_19042 core.exception.RangeError@INSTALLDIR/dmd2-2.084.0/osx/bin/../../src/phobos/std/range/package.d(12868): Range violation ---------------- ??:? _d_arrayboundsp [0x73c2b71] ??:? pure nothrow @nogc @safe std.range.padRight!(int[], int).padRight(int[], int, ulong).Result std.range.padRight!(int[], int).padRight(int[], int, ulong).Result.opSlice(ulong, ulong) [0x73aab65] ??:? _Dmain [0x73aa596]

Phobos PR 6865: https://github.com/dlang/phobos/pull/6865

dlang/phobos pull request #6865 "Fix issues 19042, 19681 - std.range.padRight bugs" was merged: https://github.com/dlang/phobos/pull/6865