Fix jsx template stripping the space between adjacent text lines (#359)

[brainkim]

Fixes #359.

The bug

The jsx tagged template collapses a newline between two text runs to nothing, where standard JSX collapses it to a single space. Multi-line prose loses the spaces at its line breaks:

jsx`<p>alpha
beta</p>`
// before: "<p>alphabeta</p>"
// after:  "<p>alpha beta</p>"

The fix

In src/jsx-tag.ts the children tokenizer trimmed trailing whitespace off a text run before every newline, treating a text–text break the same as an element-adjacent one. When a newline follows non-empty text and the next significant character in the span is not < (the next token is text, not an element), collapse the break to a single space instead of stripping it. Everything else is unchanged.

Whitespace parity (verified against esbuild + tsc)

I checked Crank's output after this fix against both transpilers the issue cites. They agree, and Crank now matches them on every in-content case:

source	Crank (fixed)	esbuild / tsc
alpha⏎beta (text–text)	alpha beta ✅	alpha beta
alpha⏎<b/> / <b/>⏎beta (element-adjacent)	stripped ✅	stripped
a b (interior spaces)	a b ✅	a b (not collapsed)
a⏎{X} / {X}⏎b (expression-adjacent)	no space ✅	no space
Hello⏎World (first-line leading)	Hello World ✅	Hello World
a⇥b (tab in text)	a⇥b ✅	a⇥b (both preserve tabs)
<b/>···<i/> (ws-only, one line)	preserved ✅	preserved
<b/>⏎<i/> (ws-only, across newline)	removed ✅	removed

The one intentional difference is template-edge whitespace: Crank trims leading/trailing whitespace at the very start and end of the whole template (e.g. jsx\⏎

⏎`), where JSX-in-a-fragment would preserve it. This is by design — the template body has no enclosing element boundary, and authors universally pad it with newlines/indentation for readability — and is covered by the existing top-level strings/newlines and whitespace` tests.

Tests

Added a #359 regression test and a parity test block in test/jsx-tag.ts covering the table above. Full suite passes; tsc --noEmit, ESLint, and Prettier clean.

🤖 Generated with Claude Code

[brainkim]

Whitespace parity investigation (for the record)

Before merging I wanted to know whether the jsx tag is now exactly JSX-faithful, so I stopped reasoning from Babel's algorithm and measured against ground truth: every case below was transpiled through both reference transpilers the issue cites — esbuild (--loader=jsx) and tsc --jsx react — and compared to Crank's output on this branch. esbuild and tsc agree with each other throughout.

Result: parity on every in-content case

source	Crank (this PR)	esbuild + tsc
alpha⏎beta (text–text)	alpha beta	alpha beta
alpha⏎<b/> / <b/>⏎beta (element-adjacent)	stripped	stripped
a b (interior spaces)	a b	a b (neither collapses)
a⏎{X} / {X}⏎b (expression-adjacent)	no space	no space
Hello⏎World (first-line leading)	Hello World	Hello World
a⇥b (tab in text)	a⇥b	a⇥b
<b/>···<i/> (ws-only, one line)	preserved	preserved
<b/>⏎<i/> (ws-only, across a newline)	removed	removed

These are locked in by the matches JSX whitespace handling (verified against esbuild + tsc) test block.

Two findings worth recording

• Tabs in text are not a divergence. Babel converts tab→space in text nodes, but esbuild and tsc both preserve tabs — same as Crank. So there is nothing to change here; the de-facto reference behavior already matches.
• Expression-adjacent newlines are not a special case. JSX strips the newline there too (the text node's only non-empty line is the adjacent one), so Crank's behavior matches rather than being a "conservative" limitation.

The one intentional difference

Template-edge whitespace. Crank trims leading/trailing whitespace at the very start and end of the whole template (jsx\⏎

⏎`), where JSX-in-a-fragment would preserve it. This stays divergent on purpose: a template body has no enclosing element boundary, and authors pad it with newlines/indentation for readability — preserving it would inject spurious whitespace text nodes into every multi-line template. It's covered by the existing top-level stringsandnewlines and whitespace` tests.

The escaped-newline \ affordance is inherent to template literals (no JSX analog) and is kept.

Bottom line: #359's fix brings the jsx tag to full whitespace parity with both reference transpilers for in-content text; the only remaining difference is the deliberate, necessary template-edge trimming.