Semantic Diff

#8876 Add provisional %raw syntax for fixed external arguments

7 commits, rendered from their records.

Summary

Range	Commits	Changelog	Areas	JS output changes	Formats	Failed checks
`b3c4184fa5322e6b37b13b5a4620b2fee94c87df..pr-8876`	7	🚀 New feature		0	none	10

Changelog draft

🚀 New feature

Add %raw(...) arguments for externals, for example external assign: (%raw("{}"), t) => t = "Object.assign". The string contains the raw JavaScript value supplied by the binding, and the argument is omitted at call sites. The legacy ` @as(json...) _ , @as("...") _, and @as(1) _ forms now emit a deprecation warning and are formatted as %raw(...)`. #8876

Files changed by more than one commit

`compiler/frontend/ast_external_process.ml`	`35fbb3f7e`, `9c6a5226c`
`compiler/ml/classify_function.ml`	`35fbb3f7e`, `393ccaf43`, `e37bf0db3`, `133fd8e28`
`tests/ounit_tests/ounit_ast_mapper0_tests.ml`	`35fbb3f7e`, `393ccaf43`
`tests/ounit_tests/ounit_flow_parser_tests.ml`	`35fbb3f7e`, `393ccaf43`, `e37bf0db3`, `133fd8e28`
`tests/syntax_tests/data/printer/typexpr/expected/fixedExternal.res.txt`	`35fbb3f7e`, `1bd4f353e`
`tests/syntax_tests/data/printer/typexpr/fixedExternal.res`	`35fbb3f7e`, `1bd4f353e`

`b3c4184fa5322e6b37b13b5a4620b2fee94c87df..pr-8876`

35fbb3f7e · Christoph Knittel · Oct 16, 2026

Add provisional %raw syntax for fixed external arguments

🚀 New feature

%raw("{}") writes a fixed external argument as a JavaScript literal. The @as(value) _ form is deprecated and formats as %raw(...).

🚀 New featureAdd %raw(...) arguments for externals, for example external assign: (%raw("{}"), t) => t = "Object.assign". The string contains the raw JavaScript value supplied by the binding, and the argument is omitted at call sites. The legacy ` @as(json...) _ , @as("...") _, and @as(1) _ forms now emit a deprecation warning and are formatted as %raw(...)`. #8876

Changelog fragment changes/raw-external-arguments.feature.md
No Tests trailer
Magic numbers bumped: ast_impl ResImpl01318, ast_intf ResIntf01318
v0 PPX bridge changes; ast-mapping fixture or mapper unit test in the diff
2 new super_errors fixtures; ERROR_VARIANTS.md unchanged

71 files · +936 −207 · changelog 1 · compiler 1 · frontend 2 · typechecker 10 · syntax 3 · other 3 · runtime 9 · playground 1 · tests 41

A	`changes/raw-external-arguments.feature.md`	+1	−0
M	`compiler/ext/config.ml`	+2	−2
M	`compiler/frontend/ast_attributes.ml`	+4	−3
M	`compiler/frontend/ast_external_process.ml`	+29	−7
M	`compiler/ml/ast_fixed_arg.ml`	+57	−10
M	`compiler/ml/ast_fixed_arg.mli`	+7	−3
M	`compiler/ml/ast_iterator.ml`	+1	−0
M	`compiler/ml/ast_mapper.ml`	+1	−0
M	`compiler/ml/ast_mapper_to0.ml`	+19	−8
M	`compiler/ml/classify_function.ml`	+18	−0
M	`compiler/ml/classify_function.mli`	+5	−0
M	`compiler/ml/parsetree.ml`	+5	−3
M	`compiler/ml/pprintast.ml`	+12	−17
M	`compiler/ml/printast.ml`	+10	−7
M	`compiler/syntax/src/res_comments_table.ml`	+3	−4
M	`compiler/syntax/src/res_core.ml`	+75	−1
M	`compiler/syntax/src/res_printer.ml`	+23	−22
M	`packages/@rescript/belt/src/Belt_Array.res`	+1	−1
M	`packages/@rescript/belt/src/Belt_Array.resi`	+1	−1
M	`packages/@rescript/belt/src/Belt_Int.res`	+1	−1
M	`packages/@rescript/runtime/Stdlib_Array.res`	+1	−1
M	`packages/@rescript/runtime/Stdlib_Array.resi`	+1	−1
M	`packages/@rescript/runtime/Stdlib_Dict.res`	+4	−4
M	`packages/@rescript/runtime/Stdlib_Dict.resi`	+4	−4
M	`packages/@rescript/runtime/Stdlib_JSON.res`	+2	−2
M	`packages/@rescript/runtime/Stdlib_JSON.resi`	+2	−2
M	`packages/@rescript/runtime/Stdlib_Object.res`	+3	−3
M	`packages/@rescript/runtime/Stdlib_RegExp.res`	+2	−2
M	`packages/@rescript/runtime/Stdlib_RegExp.resi`	+2	−2
M	`packages/dev-playground/src/Bindings.res`	+6	−3
M	`tests/analysis_tests/tests-reanalyze/deadcode/expected/deadcode.txt`	+1	−1
M	`tests/analysis_tests/tests/src/CompletionJsx.res`	+1	−1
M	`tests/build_tests/react_ppx/src/React.res`	+5	−7
A	`tests/build_tests/super_errors/expected/raw_external_arg_not_literal.res.expected`	+8	−0
A	`tests/build_tests/super_errors/expected/raw_external_arg_optional.res.expected`	+8	−0
A	`tests/build_tests/super_errors/fixtures/raw_external_arg_not_literal.res`	+1	−0
A	`tests/build_tests/super_errors/fixtures/raw_external_arg_optional.res`	+1	−0
M	`tests/dependencies/rescript-react/src/React.res`	+7	−8
M	`tests/dependencies/rescript-react/src/ReactDOMStyle.res`	+2	−2
M	`tests/dependencies/rescript-react/src/RescriptReactRouter.res`	+2	−2
M	`tests/ounit_tests/ounit_ast_mapper0_tests.ml`	+2	−0
M	`tests/ounit_tests/ounit_flow_parser_tests.ml`	+32	−0
M	`tests/ounit_tests/ounit_string_literal_tests.ml`	+34	−0
M	`tests/syntax_tests/data/ast-mapping/FixedExternal.res`	+1	−0
M	`tests/syntax_tests/data/ast-mapping/expected/FixedExternal.res.txt`	+93	−5
M	`tests/syntax_tests/data/ast-mapping/expected/FunctionsAndArrows.res.txt`	+14	−1
A	`tests/syntax_tests/data/parsing/errors/typexpr/expected/fixedExternalDuplicate.res.txt`	+10	−0
A	`tests/syntax_tests/data/parsing/errors/typexpr/expected/fixedExternalPosition.res.txt`	+11	−0
A	`tests/syntax_tests/data/parsing/errors/typexpr/expected/fixedExternalTyped.res.txt`	+10	−0
A	`tests/syntax_tests/data/parsing/errors/typexpr/fixedExternalDuplicate.res`	+1	−0
A	`tests/syntax_tests/data/parsing/errors/typexpr/fixedExternalPosition.res`	+1	−0
A	`tests/syntax_tests/data/parsing/errors/typexpr/fixedExternalTyped.res`	+1	−0
M	`tests/syntax_tests/data/printer/other/expected/attributes.res.txt`	+76	−4
M	`tests/syntax_tests/data/printer/typexpr/expected/fixedExternal.res.txt`	+234	−9
M	`tests/syntax_tests/data/printer/typexpr/fixedExternal.res`	+10	−0
M	`tests/tests/src/AsInUncurriedExternals.mjs`	+8	−1
M	`tests/tests/src/AsInUncurriedExternals.res`	+11	−4
M	`tests/tests/src/UncurriedExternals.res`	+1	−1
M	`tests/tests/src/braced_attribute_payload.res`	+1	−1
M	`tests/tests/src/bs_auto_uncurry.res`	+2	−2
M	`tests/tests/src/bs_splice_partial.res`	+2	−2
M	`tests/tests/src/external_ppx.mjs`	+1	−1
M	`tests/tests/src/external_ppx.res`	+4	−4
M	`tests/tests/src/external_ppx2.res`	+1	−1
M	`tests/tests/src/ffi_js_test.res`	+2	−2
M	`tests/tests/src/gpr_1170.res`	+2	−2
M	`tests/tests/src/gpr_1484.res`	+1	−1
M	`tests/tests/src/mario_game.res`	+1	−1
M	`tests/tests/src/prepend_data_ffi.mjs`	+5	−5
M	`tests/tests/src/prepend_data_ffi.res`	+24	−23
M	`tests/tests/src/record_name_test.res`	+2	−2

with Claude Opus 5.5

70da6ea0d · Christoph Knittel · Sep 04, 2026

Allow slow CI builds in watch recompilation test

No Tests trailer

1 files · +3 −2 · tests 1

M rewatch/tests/watch/01-watch-recompile.sh +3 −2

393ccaf43 · Christoph Knittel · Oct 16, 2026

Reject computed keys in fixed literals

A computed object key such as [f()] runs code, so it is not a literal. Also test that a %raw fixed argument survives the v0 bridge.

No Tests trailer

3 files · +57 −1 · typechecker 1 · tests 2

M	`compiler/ml/classify_function.ml`	+10	−1
M	`tests/ounit_tests/ounit_ast_mapper0_tests.ml`	+43	−0
M	`tests/ounit_tests/ounit_flow_parser_tests.ml`	+4	−0

with Claude Opus 5.5

e37bf0db3 · Christoph Knittel · Oct 16, 2026

Validate fixed literals as strict mode JavaScript

The output is strict, so legacy octal literals such as 007 and octal escapes are rejected.

No Tests trailer

2 files · +11 −1 · typechecker 1 · tests 1

M	`compiler/ml/classify_function.ml`	+6	−1
M	`tests/ounit_tests/ounit_flow_parser_tests.ml`	+5	−0

with Claude Opus 5.5

9c6a5226c · Christoph Knittel · Oct 16, 2026

Report unused attributes on fixed arguments

As for @as(value) _, an attribute such as @ignore next to %raw has no effect.

No Tests trailer
1 new super_errors fixture; ERROR_VARIANTS.md unchanged

3 files · +35 −18 · frontend 1 · tests 2

M	`compiler/frontend/ast_external_process.ml`	+24	−18
A	`tests/build_tests/super_errors/expected/raw_external_arg_unused_attribute.res.expected`	+10	−0
A	`tests/build_tests/super_errors/fixtures/raw_external_arg_unused_attribute.res`	+1	−0

with Claude Opus 5.5

1bd4f353e · Christoph Knittel · Oct 16, 2026

Test migrating fixed values with template syntax

No Tests trailer

2 files · +47 −0 · tests 2

M	`tests/syntax_tests/data/printer/typexpr/expected/fixedExternal.res.txt`	+45	−0
M	`tests/syntax_tests/data/printer/typexpr/fixedExternal.res`	+2	−0

with Claude Opus 5.5

133fd8e28 · Christoph Knittel · Oct 17, 2026

Allow unary minus only on numbers in fixed literals

Negating an array, object or regexp can run a valueOf method.

No Tests trailer

2 files · +14 −1 · typechecker 1 · tests 1

M	`compiler/ml/classify_function.ml`	+5	−1
M	`tests/ounit_tests/ounit_flow_parser_tests.ml`	+9	−0

with Claude Opus 5.5