Feature 0 complete. addNote/addHelp bundle notes and help-blocks under a
primary diagnostic (handle from new addId/addFmtId); help blocks carry an
optional fix-it line that substitutes the suggested source. renderExtended
now renders primary -> notes -> helps with blank-line separators.
Wire the CLI to the extended renderer (renderErrors -> renderStderr) and
flip render_style default to .extended; the previous renderErrors ->
renderDebug path bypassed render() entirely, so flipping the field alone
was a no-op. 13 diagnostic snapshots re-rendered to the extended format.
Adds RenderStyle (compact/extended), renderExtended/renderExtendedOne
producing the locked Rust-style format (header, --> location arrow, blank
bar, numbered code excerpt, caret line), and dispatches render() through
a render_style field on DiagnosticList. Old render body extracted as
renderCompact and kept as the default so existing snapshots stay
unchanged — F0.3 flips the default.
renderExtendedOne builds on F0.1's extractContext. Helpers digitCount
(line-number column width) and writeRepeated (no writeByteNTimes in
modern std.Io.Writer) are file-private. Line-number column has a min
width of 2 to match Rust's visual style.
7 new tests cover single-line span with carets, warning prefix,
span-less header, triple-digit line widening the column, empty-span
single caret, multi-line span with per-line carets, and the compact-
default regression. All 15 errors tests pass via `zig test
src/errors.test.zig`; 224 regression tests green.
Surfaced gotcha: zig build test doesn't currently exercise src/*.test.zig
files because src/root.zig lacks refAllDecls; adding it exposes
pre-existing breakage in src/ir/lower.test.zig and src/ir/types.zig.
Reverted that addition — out of scope for the lang workstream; unit-test
verification uses direct zig test for now.
Adds LineInfo, ContextLines, and extractContext(allocator, source, span) to
errors.zig — a pure utility that returns the source lines covered by a span
plus columns for caret rendering. Prereq for F0.2's new render path which
will produce Rust-style multi-line diagnostics with code excerpts.
8 unit tests cover the boundary cases: single-line span, multi-line spans
(1 and 2 newlines crossed), span on an empty line, span at end-of-file
without trailing newline, empty source, and offsets beyond source.len
(clamping).
No render surface change yet; F0.2 wires this into a new render mode kept
behind a RenderStyle flag so old gcc-style output remains available during
the transition.
