Onion Practical-Quality Bar

"Practical quality" is intentionally vague, so this file pins it to a set of objectively measurable indicators. Each row has a measurement you can run and a threshold; the language has reached the bar when every row passes.

Baseline figures are the ground-truth values as of 2026-06-26 (develop @ 6a2d0e4).

#	Dimension	How to measure	Current (2026-06-26)	Pass threshold
1	Test suite	SBT_OPTS="-Xmx2g" sbt -batch test	1193 pass / 0 fail	0 failed, 0 skipped
2	Sample health	SampleProgramsSpec (compiles every run/*.on)	36 / 36 compile	all compile, no rot
3	Large programs	count of run/*.on ≥ 100 lines that run end-to-end as-is	5 (OrderReport, StatsApp, TodoManager, ShapeProcessor, TextAnalyzer)	≥ 5
4	Feature coverage	checklist below demonstrated inside the large samples	complete	every item ✓
5	Known usability bugs	implemented-but-unreachable / broken features still open	0	0
6	Docs parity	docs/guide vs docs/ja/guide count + every code block compiles	12 / 12	parity + all blocks verified
7	Diagnostics	distinct E00xx codes with EN+JA messages	~24	every common error has a dedicated code

Practical quality is reached when rows 1–7 all pass. This turns the open-ended goal "reach practical quality" into a checkable state.

Row 4 — feature coverage checklist

A feature counts as covered once it runs inside at least one large sample (run/), not just a micro-test:

• records (plain) and data-carrying enums
• plain enums
• classes with constructors and methods
• interfaces + polymorphic dispatch (ExprEval)
• top-level def with block and expression bodies
• recursion (incl. tail position)
• collection pipelines: map / filter / fold / reduce / sortedBy / groupBy / find / distinct / partition / zip / flatten
• select / pattern matching
• if / else if expressions
• while, foreach over ranges and over Map (k, v)
• nullable types with null checks
• closures stored in vals
• string interpolation #{}
• try / catch
• generics used non-trivially in a large sample (StatsApp — SafeBox[T], Pair[A,B], generic countMatches)
• extension methods used in a large sample (StatsApp, ShapeProcessor, TextAnalyzer, TodoManager)

Row 5 — currently open usability bugs (tracked)

None. The two previously tracked issues have been resolved:

1. Primitive-type extensions — fixed. extension Int { def double(): Int = self * 2 } and (5).double() now work. Extension methods on primitive receivers are registered under the boxed class name and the call target is unboxed before invoking the backing static method.
2. Top-level function called from a class method — fixed. Top-level val/var and functions are emitted as static members of the synthetic top-level class, and bare identifiers / unqualified calls in class methods fall back to these static members.