modfile: support autolambda directive

[fennoai]

Resolves #158.

• Proposal: Auto Lambda xgo#2828

What

Adds support for the autolambda directive in gox.mod and stores the parsed result in Project.AutoLambdas.

autolambda times(1), forEver(0), onKey(1)

Each name(n) entry maps a command's identifier to the number of non-lambda arguments that appear before the (implicit) trailing lambda.

Details

• New autolambda case in parseVerb (modfile/rule.go), placed after the existing pack directive.
• Must be declared after a project definition (consistent with class / import / pack).
• Multiple entries may be declared in a single directive (comma-separated) or spread across multiple autolambda lines within the same project; all entries merge into Project.AutoLambdas.
• Robust parsing over the gox.mod token stream (the tokenizer splits (, ) and , into separate tokens), with descriptive error messages for malformed entries.

Tests

Added to modfile/rule_test.go:

• TestParseAutoLambda — single directive with multiple entries.
• TestParseMultiAutoLambda — entries spread across multiple lines.
• TestParseNoAutoLambda — absence leaves AutoLambdas nil.
• TestParseAutoLambdaErr — error cases (before project, missing args, malformed name(n), invalid number, missing separators, trailing comma).

go test ./... and go vet ./modfile/ pass. go.mod / go.sum are unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.23%. Comparing base (b41b6c1) to head (5b58a95).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #159      +/-   ##
==========================================
+ Coverage   76.96%   81.23%   +4.26%     
==========================================
  Files          11       10       -1     
  Lines         890      906      +16     
==========================================
+ Hits          685      736      +51     
+ Misses        186      151      -35     
  Partials       19       19              

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[fennoai]

Review: autolambda directive parser

The change is clean and well-structured: parseAutoLambdas is a pure, testable function, isIdent is the right choice over parseSymbol (autolambda names are lowercase method names), strconv.Atoi correctly rejects overflow and non-numeric input while the explicit nArgs < 0 check handles negatives, and the error paths are thoroughly tested. Build and the new tests pass locally.

Two concrete findings are left inline. Additional minor observations below.

Minor observations (non-blocking):

• modfile/rule.go:95 — the AutoLambdas field comment ("number of parameters before auto lambda") is terse; expanding it to explain what the count controls would help future readers.
• isIdent restricts command names to ASCII [A-Za-z_][A-Za-z0-9_]*, stricter than the underlying modfile tokenizer. Almost certainly intentional, but worth confirming XGo command names are never non-ASCII.
• No test pins the duplicate-name semantics (same name within one directive or across two autolambda directives). Whatever behavior is chosen for the inline finding below, add a test to lock it in.