[christophwille]

Draft: one of three candidate ports of ilspycmd off McMaster.Extensions.CommandLineUtils (System.CommandLine in #4305, ConsoleAppFramework, CliFx), to be compared side by side. This one uses CliFx 3.0.1 (source-generated since 3.0; no runtime dependencies on net10.0).

The contract tests from #4303 are the oracle: ICSharpCode.ILSpyCmd.Tests is green (111 tests, the 108 existing ones plus three rows added here that pin spellings the evaluated libraries would otherwise change: a bare -usepdb followed by a file name, a multi-value option followed by a file name, and -pd being an error rather than -p -d). Error and help wording changed; option and argument behavior did not.

Shape (the same in all three drafts)

• ILSpyCmdProgram is now the engine with plain settable properties; it validates the option combination itself (ValidateUsage: input files, -r directories, -usepdb/settings files exist, -p/-d need -o) and runs the request. It no longer knows a parser. ValidationAttributes.cs and the unused IHostEnvironment are gone, so Microsoft.Extensions.Hosting leaves the project too.
• LegacyCommand is the file that knows the library. It defines the verb-less command line and binds it into an ILSpyCmdProgram. Retiring the verb-less form later means deleting it (here: together with LegacyArgumentRewriter).

How CliFx fits

• LegacyCommand is CliFx's default command ([Command] without a name, a partial class with [CommandOption]/[CommandParameter] properties and a generated Descriptor). Verbs become named commands ([Command("dump table")], multi-word names nest by prefix) registered next to it; routing takes the longest leading token sequence that names a command, otherwise the default command. A file literally named like a verb needs ./verb.
• CliFx cannot parse the legacy grammar directly. Its parser reads positional parameters only until the first option, lets an option collect every following bare token (-r dir sample.dll would make the assembly a reference path), splits every single-dash token into one-letter options (-il is -i -l, short names are one char), and has no :/= delimiters. LegacyArgumentRewriter therefore turns the raw arguments into [input files..., --name value ...] first, using the generated descriptor for arity and short names plus a five-entry table for the multi-letter aliases (-il -lv -ds -genpdb -usepdb). It also rejects what CliFx would misread (unknown options, -pd, --) with the old exit code.
• CliFx reports every usage mistake it detects itself with exit code 1 (not configurable) and prints the help text after it; ilspycmd never used 1, so the host maps 1 to EX_USAGE. The command's own exit code is read back from the instance, which is handed to CliFx through UseTypeInstantiator.
• CliFx's stock enum conversion lets a bad -lv value escape as an exception with a stack trace; a small ScalarInputConverter throws CommandException(..., 64) instead, which CliFx prints as a one-line error.
• CliFx's SystemConsole opens the raw standard handles and bypasses Console.SetOut; the host passes a FakeConsole over two tiny write-only streams that hand the bytes back to Console.Out/Console.Error (this is also what lets the in-process tests see the output). Ctrl+C registration is lost; the tool never registered one.
• No hidden options exist in CliFx: the developer switch --generate-diagrammer-json-only is taken out of the arguments by the rewriter and set on the command directly.

Behavioral differences left (none pinned by the contract)

• Multi-letter aliases cannot appear in the help's option column (only in the description text).
• Help layout follows CliFx (USAGE/DESCRIPTION/PARAMETERS/OPTIONS, Default: <false>. on every flag, a Choices: list for --languageversion, the Remarks/Examples under DESCRIPTION, the version in the header); the README block was regenerated from the Release build.
• Long option names are matched case-insensitively by CliFx once they reach it; the rewriter itself is exact.

AOT

CliFx 3 binds through generated typed descriptors, so <TrimmerRootAssembly Include="ilspycmd" /> and the McMaster value-parser warm-up are gone. IlcTreatWarningsAsErrors=false stays for Mono.Cecil. Not run locally: the Native AOT publish. The IlspyCmdRidPackages CI job (win-x64/linux-x64 publish plus smoke test) is the gate for this PR.

Assisted-by: Claude:claude-fable-5-1:Claude Code