Fixes#18583.
## Problem
Several stdlib collection types compute the separator for `$` using
`result.len > 1`, where `result` starts as the opening bracket (`"["` or
`"{"`). This breaks when a collection element type has a `$` that
returns an empty string: `result.len` stays at 1 after the first item
contributes nothing, so the separator is never inserted for subsequent
items.
```nim
import std/deques
type Test = object
proc `$`(x: Test): string = ""
echo [Test(), Test()].toDeque # prints [] — expected [, ]
```
## Fix
Replace the length check with an explicit `first` flag in all affected
modules: `deques`, `heapqueue`, `lists`, `critbits`, and `strtabs`.
## Tests
Regression tests added to `tdeques`, `theapqueue`, and `tlists` using a
local type whose `$` returns `""`. All three test files pass with `nim c
-r`.
## Notes
I work with Claude as a co-processor. I'm 56, came to programming late,
and this is genuinely how I learn and contribute. I understand what I'm
submitting, but I didn't write it alone. If your project prefers
human-only contributions, just say so and I'll close without friction.
---------
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
* Unwind just the "pseudorandom probing" (whole hash-code-keyed variable
stride double hashing) part of recent sets & tables changes (which has
still been causing bugs over a month later (e.g., two days ago
https://github.com/nim-lang/Nim/issues/13794) as well as still having
several "figure this out" implementation question comments in them (see
just diffs of this PR).
This topic has been discussed in many places:
https://github.com/nim-lang/Nim/issues/13393https://github.com/nim-lang/Nim/pull/13418https://github.com/nim-lang/Nim/pull/13440https://github.com/nim-lang/Nim/issues/13794
Alternative/non-mandatory stronger integer hashes (or vice-versa opt-in
identity hashes) are a better solution that is more general (no illusion
of one hard-coded sequence solving all problems) while retaining the
virtues of linear probing such as cache obliviousness and age-less tables
under delete-heavy workloads (still untested after a month of this change).
The only real solution for truly adversarial keys is a hash keyed off of
data unobservable to attackers. That all fits better with a few families
of user-pluggable/define-switchable hashes which can be provided in a
separate PR more about `hashes.nim`.
This PR carefully preserves the better (but still hard coded!) probing
of the `intsets` and other recent fixes like `move` annotations, hash
order invariant tests, `intsets.missingOrExcl` fixing, and the move of
`rightSize` into `hashcommon.nim`.
* Fix `data.len` -> `dataLen` problem.
* Add neglected API call `find` to heapqueue.
* Add a changelog.md entry, `since` annotation and rename parameter to be
`heap` like all the other procs for consistency.
* Add missing import.
