Print @as names and external strings as ReScript string literals by cknitt · Pull Request #9143 · rescript-lang/rescript

cknitt · 2026-10-30T16:14:43Z

The printer of declarations escaped strings the OCaml way: %S for the @as name of a constructor, String.escaped for the @as name of a field and for every string of a printed external (@module, @scope, inline string constants). Both write non-ASCII bytes as decimal escapes like \195\169, which ReScript reads back as other characters. A generated interface for an applied functor then named @as("prénom") as prÃ©nom at run time, and error messages and hover showed the escapes.

The strings are now encoded with String_literal.encode_js_string, which keeps valid UTF-8 and escapes only what a string literal needs, as #9136 does for @tag names.

Before:  type t = @as("\195\169") A({@as("pr\195\169nom") name: int}) | @as("a\"b") B
After:   type t = @as("é") A({@as("prénom") name: int}) | @as("a\"b") B

New tests: tests/build_tests/super_errors/fixtures/as_names_printed_as_written.res (constructor and field @as with non-ASCII letters and a quote) and external_strings_printed_as_written.res (@module and @scope with non-ASCII letters).

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kbf3gLpf7RN1MiRcubPgRn

github-actions · 2026-10-30T16:15:02Z

Changelog

🐛 Bug fix

Print the @as names of fields and constructors and the strings of externals as they are written, so that non-ASCII letters are no longer turned into escapes that read back as other characters in error messages, hover and generated interfaces.

Semantic Diff

1 commit · Full page

Print @as names and external strings as ReScript string literals

_{4676523 · cknitt + Claude · Oct 30, 2026, 16:14 UTC}

Why

The printer wrote the @as name of a constructor with OCaml's %S and the @as name of a field and the strings of an external with String.escaped. Both turn non-ASCII bytes into decimal escapes such as \195\169, which ReScript reads back as other characters: an interface written by createInterface for an applied functor then gave its fields and constructors other runtime names than the implementation (#9142). They are now encoded with String_literal.encode_js_string, which keeps valid UTF-8 and escapes only what a string literal needs.

Diagnostic modified (@as names of a constructor and a field)

module M: {
  type t = | @as("é") A({@as("prénom") name: string}) | @as("a\"b") B
} = {
  type t = | @as("é") A({@as("prénom") name: int}) | @as("a\"b") B
}

diagnostic

 Actual declaration (as_names_printed_as_written.res:6:3-66):
-  type t = @as("\195\169") A({@as("pr\195\169nom") name: int}) | @as("a\"b") B
+  type t = @as("é") A({@as("prénom") name: int}) | @as("a\"b") B

Diagnostic modified (strings of an external)

module M: {
  @module("ünïcode") @scope("ëxtra")
  external f: int => int = "f"
} = {
  @module("ünïcode") @scope("ëxtra")
  external f: string => int = "f"
}

diagnostic

 Actual declaration (external_strings_printed_as_written.res:6:3-7:33):
-  @val @module("\195\188n\195\175code") @scope("\195\171xtra") external f: string => int = "f"
+  @val @module("ünïcode") @scope("ëxtra") external f: string => int = "f"

Format modified (createInterface for an applied functor)

module Make = (X: {type t}) => {
  type record = {@as("prénom") name: X.t}
}
module Applied = Make({
  type t = string
})

rescript · Before: the field is named "prÃ©nom" when the interface is read back

 module Applied: {
-  type record = {@as("pr\195\169nom") name: string}
+  type record = {@as("prénom") name: string}
 }

codecov · 2026-10-30T16:20:24Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.74%. Comparing base (7249c11) to head (4676523).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9143   +/-   ##
=======================================
  Coverage   81.73%   81.74%           
=======================================
  Files         460      460           
  Lines       64936    64940    +4     
=======================================
+ Hits        53076    53082    +6     
+ Misses      11860    11858    -2

Files with missing lines	Coverage Δ
compiler/ml/printtyp.ml	`72.46% <100.00%> (+0.02%)`	⬆️
compiler/syntax/src/res_outcome_printer.ml	`83.00% <100.00%> (+0.55%)`	⬆️

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pkg-pr-new · 2026-10-30T16:26:00Z

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rescript

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@rescript/win32-x64

npm i https://pkg.pr.new/@rescript/win32-x64@9143

commit: 4676523

github-actions · 2026-10-30T16:29:34Z

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-9143

cknitt · 2026-10-30T17:16:31Z

@codex review

chatgpt-codex-connector · 2026-10-30T17:16:47Z

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-30T17:18:01.005535Z	`859cef9`	Manual request

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chatgpt-codex-connector · 2026-10-30T17:17:59Z

Codex Review: Didn't find any major issues. 👍

Reviewed commit: 859cef9e2c

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@as

Why: The printer wrote the @as name of a constructor with OCaml's %S and the @as name of a field and the strings of an external with String.escaped. Both turn non-ASCII bytes into decimal escapes such as \195\169, which ReScript reads back as other characters: an interface written by createInterface for an applied functor then gave its fields and constructors other runtime names than the implementation (#9142). They are now encoded with String_literal.encode_js_string, which keeps valid UTF-8 and escapes only what a string literal needs. Diagnostic modified (@as names of a constructor and a field): Example: module M: { type t = | @as("é") A({@as("prénom") name: string}) | @as("a\"b") B } = { type t = | @as("é") A({@as("prénom") name: int}) | @as("a\"b") B } Before (diagnostic): Actual declaration (as_names_printed_as_written.res:6:3-66): type t = @as("\195\169") A({@as("pr\195\169nom") name: int}) | @as("a\"b") B After (diagnostic): Actual declaration (as_names_printed_as_written.res:6:3-66): type t = @as("é") A({@as("prénom") name: int}) | @as("a\"b") B Diagnostic modified (strings of an external): Example: module M: { @module("ünïcode") @scope("ëxtra") external f: int => int = "f" } = { @module("ünïcode") @scope("ëxtra") external f: string => int = "f" } Before (diagnostic): Actual declaration (external_strings_printed_as_written.res:6:3-7:33): @Val @module("\195\188n\195\175code") @scope("\195\171xtra") external f: string => int = "f" After (diagnostic): Actual declaration (external_strings_printed_as_written.res:6:3-7:33): @Val @module("ünïcode") @scope("ëxtra") external f: string => int = "f" Format modified (createInterface for an applied functor): Example: module Make = (X: {type t}) => { type record = {@as("prénom") name: X.t} } module Applied = Make({ type t = string }) Before (rescript): the field is named "prÃ©nom" when the interface is read back module Applied: { type record = {@as("pr\195\169nom") name: string} } After (rescript): module Applied: { type record = {@as("prénom") name: string} } Fixes: #9142 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gLpf7RN1MiRcubPgRn Signed-off-by: Christoph Knittel <ck@cca.io>

cknitt marked this pull request as ready for review October 30, 2026 17:16

cknitt force-pushed the as-name-escaping branch from 859cef9 to d2eb41e Compare October 30, 2026 17:17

cknitt force-pushed the as-name-escaping branch from d2eb41e to 70824bc Compare October 30, 2026 17:18

cknitt requested a review from cristianoc October 30, 2026 17:20

cknitt force-pushed the as-name-escaping branch from 70824bc to 4676523 Compare October 30, 2026 17:31

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