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Stop mangling tagged templates and backquoted strings#7841

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tsnobip merged 1 commit intomasterfromcompile-to-js-template-literals

Sep 4, 2025

Merged

Stop mangling tagged templates and backquoted strings#7841

tsnobip merged 1 commit intomasterfromcompile-to-js-template-literals

Sep 4, 2025

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tsnobip commentedSep 4, 2025•
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Fixes#7777,#7196.

With this PR

letquery=sql`" SELECT * FROM ${table} WHERE id = ${id}`

generates

letquery=Tagged_template_libJs.sql`" SELECT * FROM${table} WHERE id =${id}`;

It used to generate

letquery=Tagged_template_libJs.sql`\"\nSELECT * FROM${table} WHERE id =${id}`;

Backquoted strings are now compiled as backquoted strings in JS, but they are still concatenated with+ when there are interpolations, this could be improved in a subsequent PR (for v12.1?).

tsnobip force-pushed thecompile-to-js-template-literals branch from8459260 to89cb764Compare

September 4, 2025 12:20

stop mangling tagged templates and backquoted strings

a16c424

tsnobip force-pushed thecompile-to-js-template-literals branch from89cb764 toa16c424Compare

September 4, 2025 12:30

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commit:a16c424

tsnobip requested a review fromCopilot

September 4, 2025 12:43

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Sep 4, 2025

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Pull Request Overview

This PR fixes the compilation of tagged templates and backquoted strings in ReScript to preserve their original formatting in the generated JavaScript output. Previously, these were being mangled with unnecessary escape sequences.

Adds support forDBackQuotes delimiter type to preserve template literal syntax
Updates the string constant representation to track delimiter information instead of just unicode flag
Modifies the compiler pipeline to properly handle backquoted strings and tagged templates

Reviewed Changes

Copilot reviewed 46 out of 46 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/tests/src/*.mjs	Test output files showing proper backquote preservation in generated JS
compiler/frontend/external_arg_spec.ml*	Adds DBackQuotes delimiter type
compiler/frontend/ast_utf8_string_interp.ml	Updates string interpolation handling for template literals
compiler/frontend/lam_constant.ml*	Changes Const_string to use delim field instead of unicode boolean
compiler/core/*.ml	Updates constant handling throughout compiler pipeline
compiler/core/js_dump.ml	Adds backquote output support in JS generation

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compiler/frontend/ast_utf8_string_interp.ml

Comment on lines +297 to +301

		let is_template=
		Ext_list.exists e.pexp_attributes (fun ({txt},_) ->
		match txtwith
		\|"res.template"\|"res.taggedTemplate" ->true
		\|_ ->false)

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The template detection logic is duplicated in thetransform_exp function but not intransform_pat. This inconsistency could lead to different behavior between expressions and patterns. Consider extracting this logic into a helper function or ensuring consistent template detection across both functions.

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tsnobipSep 4, 2025

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this is because you can't have string interpolation in pattern matching.

compiler/frontend/ast_utf8_string_interp.ml

		Ext_string.equal optDelim.escaped_j_delimiter
		\|\|Ext_string.equal optDelim.escaped_back_quote_delimiter

		letis_unescapeds=Ext_string.equal sDelim.unescaped_js_delimiter

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Theis_unescaped function only checks for theunescaped_js_delimiter but doesn't account for the new backquote delimiter. This could lead to inconsistent behavior when processing unescaped strings with different delimiters.

Suggested change

	letis_unescapeds=Ext_string.equal sDelim.unescaped_js_delimiter
	letis_unescapeds=
	Ext_string.equal sDelim.unescaped_js_delimiter
	\|\|Ext_string.equal sDelim.escaped_back_quote_delimiter