ToFrozenDictionary function throws ArgumentOutOfRangeException exception in .Net 8 Pewview 7

[CuteLeon]

Describe the bug

ToFrozenDictionary function throws ArgumentOutOfRangeException exception in .Net 8 Pewview 7

To Reproduce

var test = Enumerable.Empty<string>().ToFrozenDictionary(s => s);

Exceptions (if any)

System.ArgumentOutOfRangeException: 'minimumLength ('-2147483638') must be a non-negative value. (Parameter 'minimumLength')
Actual value was -2147483638.'

Further technical details

.NET SDK:
Version: 8.0.100-preview.7.23376.3
Commit: daebeea8ea

Tagging subscribers to this area: @dotnet/area-system-collections
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Describe the bug

ToFrozenDictionary function throws ArgumentOutOfRangeException exception in .Net 8 Pewview 7

To Reproduce

var test = Enumerable.Empty<string>().ToFrozenDictionary(s => s);

Exceptions (if any)

System.ArgumentOutOfRangeException: 'minimumLength ('-2147483638') must be a non-negative value. (Parameter 'minimumLength')
Actual value was -2147483638.'

Further technical details

.NET SDK:
Version: 8.0.100-preview.7.23376.3
Commit: daebeea8ea

Author:	CuteLeon
Assignees:	-
Labels:	area-System.Collections, untriaged
Milestone:	-

[eiriktsarpalis]

Can reproduce, seems like this code

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.cs

Lines 154 to 170 in 55c896f

	IEqualityComparer<string> stringComparer = (IEqualityComparer<string>)(object)comparer;
	// keys and values are needed for every strategy
	string[] keys = (string[])(object)source.Keys.ToArray();
	TValue[] values = source.Values.ToArray();
	// Calculate the minimum and maximum lengths of the strings in the dictionary. Several of the analyses need this.
	int minLength = int.MaxValue, maxLength = 0;
	foreach (string key in keys)
	{
	if (key.Length < minLength) minLength = key.Length;
	if (key.Length > maxLength) maxLength = key.Length;
	}
	Debug.Assert(minLength >= 0 && maxLength >= minLength);
	// Try to create an implementation that uses length buckets, where each bucket contains up to only a few strings of the same length.
	FrozenDictionary<string, TValue>? frozenDictionary = LengthBucketsFrozenDictionary<TValue>.CreateLengthBucketsFrozenDictionaryIfAppropriate(keys, values, stringComparer, minLength, maxLength);

does not account for empty dictionary inputs. This appears to be causing this assertion

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/LengthBucketsFrozenDictionary.cs

Line 35 in 55c896f

Debug.Assert(keys.Length != 0 && keys.Length == values.Length);

to fail in debug builds. cc @adamsitnik @stephentoub

[skyoxZ]

@eiriktsarpalis It would fail eariier at Line 167: Debug.Assert(minLength >= 0 && maxLength >= minLength);

And another issue:

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.cs

Line 232 in 55c896f

return new SmallFrozenDictionary<TKey, TValue>(source);

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/SmallFrozenDictionary.cs

Line 26 in 55c896f

Debug.Assert(source.Count != 0);

Maybe something is missing to ensure source is not empty at first?

[adamsitnik]

Both the fix (#90595) and backport (#90599) got merged.