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added this pull request to stack #8907
October 18, 2026 18:28
Codecov Report❌ Patch coverage is
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## master #8905 +/- ##
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- Coverage 81.03% 81.02% -0.01%
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Files 455 456 +1
Lines 63630 63710 +80
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+ Hits 51561 51620 +59
- Misses 12069 12090 +21
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The parser no longer turns [a, ...b] and list{...a, b} into calls of
Primitive_array.spread and Primitive_list.spread marked with res.spread.
Pexp_spread keeps the items and spreads in source order, and the type
checker gives it a Texp_spread node. Translation emits new Parray_spread
and Plist_spread primitives that compile to the same runtime calls. A list
literal whose only spread is its tail stays a chain of ::.
Before (rescript):
let x = [...[1, 2], 3, ...[]]
let y = @attr list{...xs, ...list{}, 1}
After (rescript):
let x = [...[1, 2], 3, ...[]]
let y = @attr list{...xs, ...list{}, 1}
Source: the old formatter printed [1, 2, 3, ] and list{...xs, , 1}
without the attribute; the new one prints the input unchanged
(tests/syntax_tests/data/printer/expr).
Review: Why do the generated item groups have ghost locations? The v0
encoding has no marker on them, and the ghost flag tells a group of items
from an array or list literal that is spread. A call built by a PPX with
real locations decodes to spreads only, which concatenates the same values.
Review: Why does the typed node hold the concatenated parts rather than the
elements? The parts are the arrays and cons chains the runtime call takes,
so the items keep the errors of array and list literals and translation
needs no list building of its own.
Area: syntax printer typechecker lambda codegen analysis reanalyze tests
Output: unchanged, tests/tests JS byte-identical after a rebuild; a
combinatorial harness of all item/spread sequences up to length 4 compiles
to identical JS with the old and new bsc
Formatting: changed spreads of array and list literals and attributes on
literals with spreads are kept; comments in list spreads stay in place
Formats: ast cmt
PPX: unchanged wire: the v0 encoding is the res.spread call it was, decoded
back to Pexp_spread (ast-mapping fixture SpreadLiterals.res)
Editor: unchanged: pipe completion types the literal as the runtime call;
SpreadLiterals.res covers AST dump, hints, highlighting and completion
Tests: +tests/syntax_tests/data/ast-mapping/SpreadLiterals.res
+tests/analysis_tests/tests/src/SpreadLiterals.res
+tests/build_tests/super_errors/fixtures/array_spread_type_mismatch.res
+tests/build_tests/super_errors/fixtures/list_spread_type_mismatch.res
+tests/build_tests/super_errors/fixtures/array_spread_annotation_mismatch.res
~tests/ounit_tests/ounit_ast_mapper0_tests.ml
~tests/syntax_tests/data/printer/expr/array.res
~tests/syntax_tests/data/printer/expr/list.res
~tests/syntax_tests/data/printer/comments/array.res
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EUpL6dKCiSwAeriDGRHqNr
Signed-off-by: Christoph Knittel <ck@cca.io>
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Part of #8624 (
res.spreaditem).The parser used to turn
[a, ...b]andlist{...a, b}into calls ofPrimitive_array.spread/Primitive_list.spreadwith ares.spreadattribute on the function. They are now aPexp_spread (kind, elements)node with items and spreads in source order, typed asTexp_spread, and translated to newParray_spread/Plist_spreadLambda primitives that compile to the same runtime calls. A list literal whose only spread is its tail (list{a, ...b}) stays a chain of::, as before.Effects
tests/testsrebuilds byte-identical, and every item/spread sequence up to length 4 (arrays and lists, top level and in functions) compiles to the same JS with the old and newbsc.[...[1, 2], 3, ...[]]printed as[1, 2, 3, ](invalid), andlist{...xs, ...list{}, 1}aslist{...xs, , 1}@attr [1, ...a]→[1, ...a])This has type: list<int>, but it's expected to have type: array<int>) instead of "This array item has type list…". With a type annotation, the mismatch is reported at the element, as for a plain array literal.to0emits the old call andfrom0decodes it back. The generated item groups get ghost locations, so a group of items can be told apart from a spread array/list literal, and the round trip is exact. A spread call built by a PPX with real locations decodes to spreads only, which concatenates the same values. Calls without the marker stay calls.ResImpl/ResIntfandcmtbumped. The new Lambda primitives come after the last constant constructor, asPdict_spreaddid.New tests
ast-mapping/SpreadLiterals.resand an ounit case for the v0 wire shape, the exact round trip, PPX-built calls and unmarked callssuper_errors:array_spread_type_mismatch,list_spread_type_mismatch,array_spread_annotation_mismatchSpreadLiterals.res(AST dump, hints, highlighting, pipe completion)A stacked follow-up will fix a formatter bug that predates this PR: a line comment inside a literal used as a
switch/if/try/loop operand moves on every reformat.🤖 Generated with Claude Code
https://claude.ai/code/session_01EUpL6dKCiSwAeriDGRHqNr