ILVerify: list the error names in ilverify --help --verbose? #136056

TL;DR: ILVerify's --ignore-error and --ignore-error-file match error names that the tool does not list anywhere and does not always print. I propose that ilverify --help --verbose print those names after the usual help text, with each verification error's message; plain --help would not change. I ask whether you would take a PR, whether --help --verbose is the right trigger, and whether the type system names should be listed.

--ignore-error and --ignore-error-file take regular expressions that ILVerify matches against error names. Verification errors use VerifierError names such as StackUnexpected. Errors from the type system, such as a type that fails to load or a missing method, use ExceptionStringID names such as ClassLoadGeneral when ILVerify keeps the name. An error with neither name, such as an exception thrown while verifying a method, matches as None. The matching is in ShouldIgnoreVerificationResult in src/coreclr/tools/ILVerify/Program.cs.

The tool does not list these names anywhere, and its output does not always show them: errors found while verifying a type print only their message, and a method error that matches as None is printed as [IL]: Error []: .... A user may have to read VerifierError.cs and ExceptionStringID.cs to find a name.

I'd like to propose that ilverify --help --verbose prints the names after the usual help text, with each verification error's message. Plain --help would not change.

It would add no new error messages to maintain: the messages are the existing ones in Strings.resx, read at run time. ILVerify already compiles src/coreclr/tools/Common/CommandLineHelpers.cs, whose UseExtendedHelp appends text after the help for crossgen2, ILCompiler and dotnet-pgo. ILVerify would call it next to UseVersion(), with a callback that checks --verbose.

I tried this locally on main, adding 24 lines to ILVerifyRootCommand.cs and Program.cs and changing one. With --help --verbose, the end of the output looks like this:

  -?, -h, --help                           Show help and usage information
  -v, --version                            Show version information

Verification errors (--ignore-error matches these names):
  UnknownOpcode: Unknown opcode.
  MethodFallthrough: Fall through end of the method without returning.
  EHClauseOutOfRange: Exception handling clause bounds outside code size.
  ...
  UnalignedAlignment: Alignment specified for 'unaligned.' must be 1, 2, or 4.

Type system errors (--ignore-error also matches these names):
  ClassLoadGeneral
  ClassLoadExplicitGeneric
  ...
  AmbiguousMatchUnsafeAccessor

An error with neither kind of name, such as an exception while verifying a method, matches None.

That is 124 verification errors and 25 type system errors. Five messages contain placeholders such as '{0}', which ILVerify fills in when it reports the error; the list would show them unfilled.

Questions:

1. Would you take a PR for this?
2. Is --help --verbose the right trigger? A dedicated option, such as --help --error-codes or a standalone --list-errors, would have its own help entry. The help entry for --verbose only says "Verbose output".
3. Should the type system names be listed? --ignore-error already matches them, but they come from the shared type system, which you said on #135989 should not be presented as something others can depend on.