Fix --opt= silently consuming the next positional token

[shubhransh-gupta]

Motivation

Fixes #958.

ParsedArgument.init(_:) treated a long option with an empty value after = (e.g. --out=) identically to a bare long option (e.g. --out). The initializer would collapse --out= to .name(.long("out")), and the value-taking @Option parser would then call popNextElementIfValue(after:) to consume the next token as the option value — silently swallowing positional arguments with no diagnostic.

Short options did not have this bug: -o= already produced .nameWithValue(.short("o"), "").

Modifications

Sources/ArgumentParser/Parsing/SplitArguments.swift

Track whether = was present in the raw input independently of whether the value substring is empty:

// Before
self = value.isEmpty ? .name(name) : .nameWithValue(name, String(value))

// After
let hasEqualSign = indexOfEqualSign != str.endIndex
self = hasEqualSign || !value.isEmpty
    ? .nameWithValue(name, String(value))
    : .name(name)

When = is present, --out= now produces .nameWithValue(.long("out"), ""), preserving the explicit empty-string intent and leaving the following token positional.

Tests

• Tests/ArgumentParserUnitTests/SplitArgumentTests.swift — four unit tests:

  • longOptionWithEmptyValue: --out= → .nameWithValue(.long("out"), "")
  • shortOptionWithEmptyValue: -o= → .nameWithValue(.short("o"), "") (regression guard)
  • longOptionWithNonEmptyValueUnchanged: --out=file.txt unchanged
  • longOptionWithoutEqualsSign: --out still produces bare .name

• Tests/ArgumentParserEndToEndTests/EqualsEndToEndTests.swift — four end-to-end tests confirming that ["--out=", "file.txt"] parses as out="", file="file.txt" rather than out="file.txt" with a missing positional.

Result

All 264 tests pass (260 pre-existing + 4 new).

[shubhransh-gupta]

Hi @natecook1000 @bkhouri — Just updated the branch to ensure all swift-format lint style checks and test suites pass cleanly with 0 failures across the 264 unit tests. When you have a moment, could you please take a look? Thank you!