Match the MA0110 regex arguments by parameter instead of position

[meziantou]

Problem

Roslyn lists the arguments of an operation in evaluation order, so explicitly reordered named arguments do not line up with the parameters. UseRegexSourceGeneratorAnalyzer nevertheless recorded fixed indices for the pattern, the options and the match timeout, and UseRegexSourceGeneratorFixer removed and lifted the arguments at those indices.

For this valid input:

Regex.IsMatch(pattern: "a", input: "b")

the fix produced:

[GeneratedRegex("b")]
private static partial Regex MyRegex { get; }
// ...
MyRegex.IsMatch(pattern: "a")

The pattern was taken from the wrong argument, and the generated call does not compile (CS1501) even after the real Regex source generator runs. The constructor and every supported static Regex method shared the same positional assumption. The analyzer's constant check was positional too, so it validated input instead of pattern.

What changed

UseRegexSourceGeneratorAnalyzer

• The pattern, the options and the match timeout arguments are located from IArgumentOperation.Parameter (pattern, options, matchTimeout) instead of a hardcoded position, and the resolved indices are what the diagnostic properties carry.
• The constant check applies to exactly those three arguments, replacing the positional skip index 0 (and index 2 for Replace) loops.
• An overload with a parameter that is neither lifted nor a known runtime parameter (input, replacement, evaluator) is no longer reported: the code fixer would otherwise silently drop that argument.
• The IsMatch/Match/Matches/Split and Replace branches collapse into a single path, as parameter identity makes the per-method shapes irrelevant.

UseRegexSourceGeneratorFixer

• Argument removal moves to a shared GetRemainingArgumentSyntaxes helper used by both the type-declaration and the top-level-statement paths. It keeps the surviving arguments in their source (evaluation) order with their name: colons intact, so the evaluation order of the runtime arguments is preserved.
• RegisterCodeFixesAsync validates the semantic model, the Regex / GeneratedRegexAttribute / RegexOptions symbols, the operation kind and the reported indices before registering either code action, following the fixer convention in AGENTS.md. Index lookups are bounds checked.

No name translation is needed when switching from the static to the instance overload: the two sets of parameters use identical names (input, replacement, evaluator). The tests compile the fixed code with the real source generator, so any mismatch would surface as CS1501.

Tests

Six tests added to UseRegexSourceGeneratorAnalyzerTests:

• RegexIsMatch_NamedArgumentsInReverseOrder (the reported case, partial method)
• RegexIsMatch_NamedArgumentsInReverseOrder_PartialProperty (the reported case, partial property)
• RegexIsMatch_Options_Timeout_NamedArgumentsInReverseOrder (all four arguments reversed)
• RegexReplace_NamedArgumentsInReverseOrder
• NewRegex_Options_Timeout_NamedArgumentsInReverseOrder (constructor)
• RegexIsMatch_NonConstantPatternPassedAsNamedArgument (no diagnostic; previously the positional check looked at input)

Verification

• dotnet build — succeeded, 0 warnings.
• dotnet test tests/Meziantou.Analyzer.Test/Meziantou.Analyzer.Test.roslyn5.9.csproj — 4186/4186 passing.
• MA0110 tests on every Roslyn version — 41/41 on roslyn4.8 and roslyn4.14, 59/59 on roslyn5.0, roslyn5.6 and roslyn5.9.
• dotnet run --project src/DocumentationGenerator — exit code 0, no markdown changes (no rule metadata changed).