Close #33

See the changelog and test case for more information

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes will be documented in this file.
 
 This document is written according to the [Keep a Changelog][kac] style.
 
+## 0.16.1
+
+This is a hotfix for [Issue #33], filed by GitHub user [@jonas-schievink].
+`BitVec::reserve` computed an incorrect element count to pass to `Vec::reserve`,
+causing `BitVec::resize` to panic when its `BitVec::reserve` call failed to
+sufficiently allocate memory before `BitVec::set_len` expanded into the memory
+it expected to be present.
+
 ## 0.16.0
 
 ### Added
@@ -569,6 +577,7 @@ Initial implementation and release.
 [@GeorgeGkas]: https://github.com/GeorgeGkas
 [@caelunshun]: https://github.com/caelunshun
 [@geq1t]: https://github.com/geq1t
+[@jonas-schievink]: https://github.com/jonas-schievink
 [@koushiro]: https://github.com/koushiro
 [@overminder]: https://github.com/overminder
 [@ratorx]: https://github.com/ratorx
@@ -582,5 +591,6 @@ Initial implementation and release.
 [Issue #15]: https://github.com/myrrlyn/bitvec/issues/15
 [Issue #16]: https://github.com/myrrlyn/bitvec/issues/16
 [Issue #28]: https://github.com/myrrlyn/bitvec/issues/28
+[Issue #33]: https://github.com/myrrlyn/bitvec/issues/33
 [`Sync`]: https://doc.rust-lang.org/stable/core/marker/trait.Sync.html
 [kac]: https://keepachangelog.com/en/1.0.0/

Cargo.toml

@@ -6,7 +6,7 @@
 
 [package]
 name = "bitvec"
-version = "0.16.0"
+version = "0.16.1"
 authors = [
 	"myrrlyn <self@myrrlyn.dev>",
 ]

src/vec/api.rs

@@ -105,7 +105,7 @@ where C: Cursor, T: BitStore {
 			BitPtr::<T>::MAX_BITS,
 		);
 		let (total_elts, _) = self.pointer.head().span(newlen);
-		if let Some(extra) = total_elts.checked_sub(self.capacity) {
+		if let Some(extra) = total_elts.checked_sub(self.pointer.elements()) {
 			self.do_unto_vec(|v| v.reserve(extra));
 		}
 	}

tests/issue_33.rs

@@ -0,0 +1,40 @@
+/*! Test case for [Issue #33], provided by GitHub user [@jonas-schievink].
+
+This report discovered an error in the implementation of `BitVec::reserve`,
+which caused it to fail to reällocate in certain conditions.
+
+The error was that the `reserve` method was testing the reservation amount
+passed in to `Vec::reserve` against the currently-allocated *capacity*, not the
+currently-occupied *element length*. `Vec::reserve` expects the difference to be
+against the element length, so `BitVec::reserve` was estimating too few elements
+and `Vec::reserve` did not see the request amount as requiring a reällocation.
+
+`BitVec::reserve` now tests the reservation amount against the current element
+length, which produces the correct reservation request for `Vec::reserve`,
+fixing the error.
+
+[Issue #33]: //github.com/myrrlyn/bitvec/issues/33
+[@jonas-schievink]: //github.com/jonas-schievink
+!*/
+
+#[cfg(feature = "alloc")]
+use bitvec::prelude::*;
+
+#[cfg(feature = "alloc")]
+#[test]
+fn issue_33() {
+	let mut swdio = BitVec::<LittleEndian, u8>::new();
+
+	swdio.resize(64, true);
+
+	let mut seq = 0xE79E; // LSb first
+	for _ in 0..16 {
+		swdio.push(seq & 0b1 != 0);
+		seq >>= 1;
+	}
+
+	swdio.reserve(64);
+	swdio.resize(swdio.len() + 64, true);
+
+	swdio.resize(swdio.len() + 10, false);
+}