Files
Nim/tests/stdlib/theapqueue.nim
Rybnikov Alex 393d27b57d fix(stdlib): use first-element flag in $ for collections (#18583) (#25832)
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>
2026-05-21 13:40:35 +02:00

119 lines
2.7 KiB
Nim

discard """
matrix: "--mm:refc; --mm:orc"
"""
import std/heapqueue
import std/assertions
proc toSortedSeq[T](h: HeapQueue[T]): seq[T] =
var tmp = h
result = @[]
while tmp.len > 0:
result.add(pop(tmp))
proc heapProperty[T](h: HeapQueue[T]): bool =
for k in 0 .. h.len - 2: # the last element is always a leaf
let left = 2 * k + 1
if left < h.len and h[left] < h[k]:
return false
let right = left + 1
if right < h.len and h[right] < h[k]:
return false
true
template main() =
block: # simple sanity test
var heap = initHeapQueue[int]()
let data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0]
for item in data:
push(heap, item)
doAssert(heap == data.toHeapQueue)
doAssert(heap[0] == 0)
doAssert(heap.toSortedSeq == @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
block: # test del
var heap = initHeapQueue[int]()
let data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0]
for item in data: push(heap, item)
heap.del(0)
doAssert(heap[0] == 1)
heap.del(heap.find(7))
doAssert(heap.toSortedSeq == @[1, 2, 3, 4, 5, 6, 8, 9])
heap.del(heap.find(5))
doAssert(heap.toSortedSeq == @[1, 2, 3, 4, 6, 8, 9])
heap.del(heap.find(6))
doAssert(heap.toSortedSeq == @[1, 2, 3, 4, 8, 9])
heap.del(heap.find(2))
doAssert(heap.toSortedSeq == @[1, 3, 4, 8, 9])
doAssert(heap.find(2) == -1)
block: # test del last
var heap = initHeapQueue[int]()
let data = [1, 2, 3]
for item in data: push(heap, item)
heap.del(2)
doAssert(heap.toSortedSeq == @[1, 2])
heap.del(1)
doAssert(heap.toSortedSeq == @[1])
heap.del(0)
doAssert(heap.toSortedSeq == @[])
block: # testing the heap proeprty
var heap = [1, 4, 2, 5].toHeapQueue
doAssert heapProperty(heap)
heap.push(42)
doAssert heapProperty(heap)
heap.push(0)
doAssert heapProperty(heap)
heap.push(3)
doAssert heapProperty(heap)
heap.push(3)
doAssert heapProperty(heap)
# [0, 3, 1, 4, 42, 2, 3, 5]
discard heap.pop()
doAssert heapProperty(heap)
discard heap.pop()
doAssert heapProperty(heap)
heap.del(2)
doAssert heapProperty(heap)
# [2, 3, 5, 4, 42]
discard heap.replace(12)
doAssert heapProperty(heap)
discard heap.replace(1)
doAssert heapProperty(heap)
discard heap.pushpop(2)
doAssert heapProperty(heap)
discard heap.pushpop(0)
doAssert heapProperty(heap)
static: main()
main()
# https://github.com/nim-lang/Nim/issues/18583
type EmptyStr18583HeapQ = object
proc `$`(x: EmptyStr18583HeapQ): string = ""
proc `<`(a, b: EmptyStr18583HeapQ): bool = false
block:
var h = initHeapQueue[EmptyStr18583HeapQ]()
push(h, EmptyStr18583HeapQ())
push(h, EmptyStr18583HeapQ())
let s = $h
doAssert s == "[, ]", "got: " & s