refactor(argparse): drop the program name from argv with a list pattern

[bobzhang]

Summary

default_argv returns the process arguments without the program name. It
did so with a length guard plus an args[1:] slice:

let args = @env.args()
if args.length() > 1 {
  args[1:]
} else {
  []
}

The > 1 bound exists only because args[1:] would panic on an empty
array, so the emptiness handling is split across a comparison and a
branch. A list pattern says the same thing in one shape:

let args = @env.args()
match args {
  [_, .. rest] => rest
  [] => []
}

.. rest binds an ArrayView[String] — the same zero-copy view that
args[1:] produced — so behaviour and allocation profile are unchanged.

Sweep for similar sites

Follow-up to #4158 / #4159 (list patterns instead of manual prefix or
head handling). A structural sweep (moongrep over match blocks that
destructure the head off a sequence and return the tail with an empty
fallback, plus rg over length-guarded [1:] slices and .. rest]
patterns) found no further instances of this shape. The remaining
[.. rest]-style code in the tree — char/byte decoders peeling one
element per iteration, FixedArray::rev and debug::compact_lines
needing the last element, quickcheck shrink and ArrayView::join
reconstruction — genuinely uses the head or tail values, so a slice or
drop would not be equivalent.

Verification

• moon check argparse clean
• moon fmt --check argparse clean
• moon test argparse: 153 passed, 0 failed

Generated with SeekMoon

[Copilot]

🟢 Approval recommended

The change is a small, behavior-preserving refactor consistent with existing list-pattern usage and the PR notes indicate relevant checks/tests passed.

Pull request overview

Refactors argparse’s default_argv helper to drop the program name using a list-pattern match instead of a length guard plus slicing, preserving the existing zero-copy ArrayView[String] behavior.

Changes:

• Replace args.length() > 1 + args[1:] with match args { [_, .. rest] => rest; [] => [] } in default_argv.
• Keep allocation profile and return type (ArrayView[String]) consistent with prior behavior.

File summaries

File	Description
argparse/parser.mbt	Simplifies argv defaulting by using a list pattern to strip the program name while still returning an ArrayView[String].

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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[coveralls]

Coverage Report for CI Build 6557

Coverage remained the same at 89.19%

Details

• Coverage remained the same as the base build.
• Patch coverage: 1 uncovered change across 1 file (2 of 3 lines covered, 66.67%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
argparse/parser.mbt	3	2	66.67%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	18169
Covered Lines:	16205
Line Coverage:	89.19%
Coverage Strength:	275644.62 hits per line

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💛 - Coveralls