Compare semantic strings by value and expose path values on interfaces

[matt-edmondson]

The bug

SemanticString<T>.CompareTo(object) forwarded straight to string.CompareTo(object), which accepts only a System.String:

public int CompareTo(object? value) => WeakString.CompareTo(value: value);

Sorting a collection typed as an interface that carries no IComparable<T> — such as IPath — makes LINQ and Comparer<T>.Default fall back to that non-generic overload and hand it another semantic string, not a string. Result:

System.InvalidOperationException: Failed to compare two elements in the array.
 ---> System.ArgumentException: Object must be of type String.
   at System.String.CompareTo(Object value)
   at ktsu.Semantics.Strings.SemanticString`1.CompareTo(Object value)

Reported downstream as ktsu-dev/ImGuiApp#273, where it crashed every file dialog as soon as the listed directory held two entries of the same kind. Not platform-specific despite the report title — it reproduces anywhere.

CompareTo(object) now unwraps ISemanticString and compares underlying values. null still sorts first and unsupported types still throw ArgumentException.

Why the sort reached the boxing path at all

IPath, IFileName, IFileExtension and IDirectoryName were empty marker interfaces. Since SemanticDirectoryPath.GetContents() returns IEnumerable<IPath>, the library handed consumers a type from which the path value could not be recovered without a downcast. That is what the downstream code had to write:

AbsoluteDirectoryPath? directory = path as AbsoluteDirectoryPath;
AbsoluteFilePath? file = path as AbsoluteFilePath;
string displayPath = directory?.WeakString ?? file?.WeakString ?? string.Empty;

• All four interfaces now expose WeakString. Every implementation already had it via SemanticString<TDerived>, so no implementation changed. ToString() was the only prior option and returns string?, costing every call site a !.
• IPath declares IComparable<IPath>, so Comparer<IPath>.Default resolves to GenericComparer instead of ObjectComparer and never boxes into the non-generic path. SemanticPath<TDerived> implements it explicitly — a public overload taking IPath would make pathA.CompareTo(pathB) ambiguous against the inherited overload taking ISemanticString, because a concrete path satisfies both parameter types and neither is more specific. There's a test whose failure to compile is the regression signal for that.

Build fix

.gitattributes gains *.cs text eol=crlf to match .editorconfig, mirroring ktsu-dev/ImGuiApp@dd44580. Without it a Linux checkout produces LF working files that violate end_of_line = crlf and the repo cannot build at all — 1711 IDE0055 errors before a single line of real work.

Tests

16 new tests: CompareTo(object) with semantic strings and unsupported types, sorting via OrderBy/ThenBy/Comparer<T>.Default/List<IPath>.Sort(), WeakString through each interface, GetContents() read without downcasting, and the comparer-selection and no-ambiguity guards. Reverting the CompareTo fix fails 5 of them.

977 passed, 93 failed — the 93 are pre-existing and unrelated: path tests hard-coding Windows separators and C:\ roots, which cannot pass on Linux. Verified by stashing this branch and re-running on a clean tree: identical 93. Baseline was 961 passing.

Packs clean (Semantics.Paths sets EnablePackageValidation=false, so there's no baseline API check to trip).

Note on the version tag

Tagged [minor]. Adding members to a public interface is a source break for anyone implementing these interfaces outside the library — though no public API accepts an IPath (or any descendant) as a parameter, so an external implementation has nothing to plug into today. If you'd rather treat interface-member additions as major, retag before merge.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WFRwYRHhEmVMGvrH2BbtbW

[sonarqubecloud]

Quality Gate failed

Failed conditions
30.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud