#8905 Represent array and list literals with spreads with a Pexp_spread node

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 ::.

let x = [...[1, 2], 3, ...[]]let y = @attr list{...xs, ...list{}, 1}

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.
• 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.

Output

unchangedtests/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

changedspreads of array and list literals and attributes on literals with spreads are kept; comments in list spreads stay in place

Formats

astcmt

PPX

unchangedwire: 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

syntax tests/syntax_tests/data/+ ast-mapping/SpreadLiterals.res~ printer/expr/array.res~ printer/expr/list.res~ printer/comments/array.res

analysis+ tests/analysis_tests/tests/src/SpreadLiterals.res

super_errors tests/build_tests/+ super_errors/fixtures/array_spread_type_mismatch.res+ super_errors/fixtures/list_spread_type_mismatch.res+ super_errors/fixtures/array_spread_annotation_mismatch.res

ounit tests/ounit_tests/~ ounit_ast_mapper0_tests.ml

• Changelog fragment changes/spread-literal-errors.polish.md
• Changelog fragment changes/spread-literal-formatting.fix.md
• Changelog fragment changes/spread-literal-node.internal.md
• No committed generated JS changes
• Magic numbers bumped: ast_impl ResImpl01318, ast_intf ResIntf01318, cmt Caml1999T046
• v0 PPX bridge changes; ast-mapping fixture or mapper unit test in the diff