critbits: fix error from strictFuncs (#16877)

Previously, compiling a file containing just `import critbits` with
`nim c --experimental:strictFuncs` would produce the following error:
    critbits.nim(529, 6) Error: 'toCritBitTree' can have side effects

This was introduced by 2aed4186989e (#16564).

Fixes: #16873

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/pure/collections/critbits.nim b/lib/pure/collections/critbits.nim
index 000ea5080..dd2203e13 100644
--- a/lib/pure/collections/critbits.nim
+++ b/lib/pure/collections/critbits.nim
@@ -518,7 +518,7 @@ func commonPrefixLen*[T](c: CritBitTree[T]): int {.inline, since((1, 3)).} =
     else: c.root.byte
   else: 0
 
-func toCritBitTree*[T](pairs: openArray[(string, T)]): CritBitTree[T] {.since: (1, 3).} =
+proc toCritBitTree*[T](pairs: openArray[(string, T)]): CritBitTree[T] {.since: (1, 3).} =
   ## Creates a new `CritBitTree` that contains the given `pairs`.
   runnableExamples:
     doAssert {"a": "0", "b": "1", "c": "2"}.toCritBitTree is CritBitTree[string]
@@ -526,7 +526,7 @@ func toCritBitTree*[T](pairs: openArray[(string, T)]): CritBitTree[T] {.since: (
 
   for item in pairs: result.incl item[0], item[1]
 
-func toCritBitTree*(items: openArray[string]): CritBitTree[void] {.since: (1, 3).} =
+proc toCritBitTree*(items: openArray[string]): CritBitTree[void] {.since: (1, 3).} =
   ## Creates a new `CritBitTree` that contains the given `items`.
   runnableExamples:
     doAssert ["a", "b", "c"].toCritBitTree is CritBitTree[void]