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fix: filter out reserved words from exp.names - #504
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📝 WalkthroughWalkthroughThe PR introduces a regression test export ( Changes
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Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@src/node/scan-dirs.ts`:
- Around line 17-71: The JS_RESERVED_WORDS set is too broad and causes valid
identifier exports like "async" or "of" to be dropped; update the filtering
logic that uses JS_RESERVED_WORDS (and the related checks referenced at the
other use sites around the 201-202 area) so it only excludes tokens when they
originate from parser false-positives emitted by mlly (i.e., when metadata/flags
indicate a lexer/parser artifact), and do not apply the reserved-word filter to
explicitly declared exports or identifiers parsed as real declarations; locate
the usage of JS_RESERVED_WORDS in scan-dirs.ts and change the condition to first
detect explicit export/declaration nodes (or mlly false-positive markers) and
only then consult JS_RESERVED_WORDS.
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📒 Files selected for processing (4)
playground/composables/async-value.tssrc/node/scan-dirs.tstest/dts.test.tstest/scan-dirs.test.ts
| const JS_RESERVED_WORDS = new Set([ | ||
| // Keywords | ||
| 'abstract', | ||
| 'arguments', | ||
| 'async', | ||
| 'await', | ||
| 'break', | ||
| 'case', | ||
| 'catch', | ||
| 'class', | ||
| 'const', | ||
| 'continue', | ||
| 'debugger', | ||
| 'default', | ||
| 'delete', | ||
| 'do', | ||
| 'else', | ||
| 'enum', | ||
| 'eval', | ||
| 'export', | ||
| 'extends', | ||
| 'false', | ||
| 'finally', | ||
| 'for', | ||
| 'function', | ||
| 'if', | ||
| 'implements', | ||
| 'import', | ||
| 'in', | ||
| 'instanceof', | ||
| 'interface', | ||
| 'let', | ||
| 'new', | ||
| 'null', | ||
| 'of', | ||
| 'package', | ||
| 'private', | ||
| 'protected', | ||
| 'public', | ||
| 'return', | ||
| 'static', | ||
| 'super', | ||
| 'switch', | ||
| 'this', | ||
| 'throw', | ||
| 'true', | ||
| 'try', | ||
| 'typeof', | ||
| 'undefined', | ||
| 'var', | ||
| 'void', | ||
| 'while', | ||
| 'with', | ||
| 'yield', | ||
| ]) |
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🧩 Analysis chain
🏁 Script executed:
# First, let's look at the file structure and the relevant code
find . -name "scan-dirs.ts" -type fRepository: unjs/unimport
Length of output: 80
🏁 Script executed:
# Get the file and examine the context around lines 17-71 and 201-202
if [ -f "src/node/scan-dirs.ts" ]; then
echo "=== Lines 1-100 of scan-dirs.ts ==="
head -100 src/node/scan-dirs.ts | cat -n
fiRepository: unjs/unimport
Length of output: 2974
🏁 Script executed:
# Also check lines around 201-202
if [ -f "src/node/scan-dirs.ts" ]; then
echo "=== Lines 190-210 of scan-dirs.ts ==="
sed -n '190,210p' src/node/scan-dirs.ts | cat -n | sed 's/^/190+/'
fiRepository: unjs/unimport
Length of output: 1236
🌐 Web query:
ECMAScript specification contextual keywords async of declaration identifiers export const
💡 Result:
In the ECMAScript spec, async and of are contextual (conditional) keywords: they are “always allowed as identifiers, but also appear as keywords within certain syntactic productions” (i.e., the parser treats them as keywords only in specific grammar positions). The spec explicitly lists: as, async, from, get, meta, of, set, target. [1]
async as an identifier vs keyword
Because async is contextual, code like let async = 1; is valid in contexts where the grammar is expecting an identifier, while async function f(){} uses async in a position where the grammar gives it keyword meaning. The spec also notes an important disambiguation rule with LineTerminators: if async is followed by a line break before function / IdentifierName / (, Automatic Semicolon Insertion can kick in and async won’t be parsed as part of an async construct. [1]
of in for...of
Similarly, of can be an identifier in general, but in the specific grammar for a for...of statement, of is treated as the keyword introducing the iteration RHS (that’s why it’s in the contextual-keyword list). [1]
Why export const ... is valid (grammar path)
The module grammar allows exporting declarations directly:
ExportDeclaration : export Declaration[2]Declaration : LexicalDeclaration[2]
Andconstdeclarations are LexicalDeclarations, soexport const x = 1;is syntactically allowed viaexport Declaration → LexicalDeclaration. [2] (MDN summarizes this as: afterexportyou can uselet,const,var, function, or class declarations.) [3]
Over-broad reserved-word filtering drops legitimate declaration exports.
The filter unconditionally skips all words in JS_RESERVED_WORDS, including contextual keywords like async and of. Per ECMAScript spec, these contextual keywords are valid identifiers and can be legitimately exported: export const async = 1 and export const of = 1 are valid. The current approach prevents these valid exports from being imported, creating false negatives.
Gate the filter to only remove parser false positives from mlly, not explicitly declared exports:
Proposed safer pattern
+ const hasExplicitExportDeclaration = (name: string) => {
+ const escaped = name.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+ return new RegExp(
+ String.raw`\bexport\s+(?:const|let|var|function|class|enum)\s+${escaped}\b`,
+ 'm',
+ ).test(code)
+ }
async function toImport(exports: ESMExport[], additional?: Partial<Import>) {
for (const exp of exports) {
// ...
else if (exp.type === 'declaration') {
for (const name of exp.names) {
- if (JS_RESERVED_WORDS.has(name))
+ if (JS_RESERVED_WORDS.has(name) && !hasExplicitExportDeclaration(name))
continue
imports.push({ name, as: name, from: filepath, ...additional })Also applies to: 201-202
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@src/node/scan-dirs.ts` around lines 17 - 71, The JS_RESERVED_WORDS set is too
broad and causes valid identifier exports like "async" or "of" to be dropped;
update the filtering logic that uses JS_RESERVED_WORDS (and the related checks
referenced at the other use sites around the 201-202 area) so it only excludes
tokens when they originate from parser false-positives emitted by mlly (i.e.,
when metadata/flags indicate a lexer/parser artifact), and do not apply the
reserved-word filter to explicitly declared exports or identifiers parsed as
real declarations; locate the usage of JS_RESERVED_WORDS in scan-dirs.ts and
change the condition to first detect explicit export/declaration nodes (or mlly
false-positive markers) and only then consult JS_RESERVED_WORDS.
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2 participants
latest unimport causes a regression due to relying on
mlly'sexp.names(see unjs/mlly#303)I've raised unjs/mlly#336 to fix this at source but in the mean time might be worth this additional defensive check to avoid trying to auto-import reserved keywords
Summary by CodeRabbit
Bug Fixes
Tests