/
prefer-export-from.js
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/
prefer-export-from.js
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'use strict';
const {
isCommaToken,
isOpeningBraceToken,
isClosingBraceToken,
} = require('eslint-utils');
const MESSAGE_ID = 'prefer-export-from';
const messages = {
[MESSAGE_ID]: 'Use `export…from` to re-export `{{exported}}`.',
};
function * removeSpecifier(node, fixer, sourceCode) {
const {parent} = node;
const {specifiers} = parent;
if (specifiers.length === 1) {
yield * removeImportOrExport(parent, fixer, sourceCode);
return;
}
switch (node.type) {
case 'ImportSpecifier': {
const hasOtherSpecifiers = specifiers.some(specifier => specifier !== node && specifier.type === node.type);
if (!hasOtherSpecifiers) {
const closingBraceToken = sourceCode.getTokenAfter(node, isClosingBraceToken);
// If there are other specifiers, they have to be the default import specifier
// And the default import has to write before the named import specifiers
// So there must be a comma before
const commaToken = sourceCode.getTokenBefore(node, isCommaToken);
yield fixer.replaceTextRange([commaToken.range[0], closingBraceToken.range[1]], '');
return;
}
// Fallthrough
}
case 'ExportSpecifier':
case 'ImportNamespaceSpecifier':
case 'ImportDefaultSpecifier': {
yield fixer.remove(node);
const tokenAfter = sourceCode.getTokenAfter(node);
if (isCommaToken(tokenAfter)) {
yield fixer.remove(tokenAfter);
}
break;
}
// No default
}
}
function * removeImportOrExport(node, fixer, sourceCode) {
switch (node.type) {
case 'ImportSpecifier':
case 'ExportSpecifier':
case 'ImportDefaultSpecifier':
case 'ImportNamespaceSpecifier': {
yield * removeSpecifier(node, fixer, sourceCode);
return;
}
case 'ImportDeclaration':
case 'ExportDefaultDeclaration':
case 'ExportNamedDeclaration': {
yield fixer.remove(node);
}
// No default
}
}
function fix({
context,
imported,
exported,
exportDeclarations,
program,
}) {
const sourceCode = context.getSourceCode();
const sourceNode = imported.declaration.source;
const sourceValue = sourceNode.value;
const sourceText = sourceCode.getText(sourceNode);
const exportDeclaration = exportDeclarations.find(({source}) => source.value === sourceValue);
/** @param {import('eslint').Rule.RuleFixer} fixer */
return function * (fixer) {
if (imported.name === '*') {
yield fixer.insertTextAfter(
program,
`\nexport * as ${exported.name} from ${sourceText};`,
);
} else {
const specifier = exported.name === imported.name
? exported.name
: `${imported.name} as ${exported.name}`;
if (exportDeclaration) {
const lastSpecifier = exportDeclaration.specifiers[exportDeclaration.specifiers.length - 1];
// `export {} from 'foo';`
if (lastSpecifier) {
yield fixer.insertTextAfter(lastSpecifier, `, ${specifier}`);
} else {
const openingBraceToken = sourceCode.getFirstToken(exportDeclaration, isOpeningBraceToken);
yield fixer.insertTextAfter(openingBraceToken, specifier);
}
} else {
yield fixer.insertTextAfter(
program,
`\nexport {${specifier}} from ${sourceText};`,
);
}
}
if (imported.variable.references.length === 1) {
yield * removeImportOrExport(imported.node, fixer, sourceCode);
}
yield * removeImportOrExport(exported.node, fixer, sourceCode);
};
}
function getImportedName(specifier) {
switch (specifier.type) {
case 'ImportDefaultSpecifier':
return 'default';
case 'ImportSpecifier':
return specifier.imported.name;
case 'ImportNamespaceSpecifier':
return '*';
// No default
}
}
function getExported(identifier, context) {
const {parent} = identifier;
switch (parent.type) {
case 'ExportDefaultDeclaration':
return {
node: parent,
name: 'default',
};
case 'ExportSpecifier':
return {
node: parent,
name: parent.exported.name,
};
case 'VariableDeclarator': {
if (
parent.init === identifier
&& parent.id.type === 'Identifier'
&& !parent.id.typeAnnotation
&& parent.parent.type === 'VariableDeclaration'
&& parent.parent.kind === 'const'
&& parent.parent.declarations.length === 1
&& parent.parent.declarations[0] === parent
&& parent.parent.parent.type === 'ExportNamedDeclaration'
&& isVariableUnused(parent, context)
) {
return {
node: parent.parent.parent,
name: parent.id.name,
};
}
break;
}
// No default
}
}
function isVariableUnused(node, context) {
const variables = context.getDeclaredVariables(node);
/* istanbul ignore next */
if (variables.length !== 1) {
return false;
}
const [{identifiers, references}] = variables;
return identifiers.length === 1
&& identifiers[0] === node.id
&& references.length === 1
&& references[0].identifier === node.id;
}
function * getProblems({
context,
variable,
program,
exportDeclarations,
}) {
const {identifiers, references} = variable;
if (identifiers.length !== 1 || references.length === 0) {
return;
}
const specifier = identifiers[0].parent;
const imported = {
name: getImportedName(specifier),
node: specifier,
declaration: specifier.parent,
variable,
};
for (const {identifier} of references) {
const exported = getExported(identifier, context);
if (!exported) {
continue;
}
/*
There is no substitution for:
```js
import * as foo from 'foo';
export default foo;
```
*/
if (imported.name === '*' && exported.name === 'default') {
return;
}
yield {
node: exported.node,
messageId: MESSAGE_ID,
data: {
exported: exported.name,
},
fix: fix({
context,
imported,
exported,
exportDeclarations,
program,
}),
};
}
}
/** @param {import('eslint').Rule.RuleContext} context */
function create(context) {
const variables = [];
const exportDeclarations = [];
return {
'ImportDeclaration[specifiers.length>0]'(node) {
variables.push(...context.getDeclaredVariables(node));
},
// `ExportAllDeclaration` and `ExportDefaultDeclaration` can't be reused
'ExportNamedDeclaration[source.type="Literal"]'(node) {
exportDeclarations.push(node);
},
* 'Program:exit'(program) {
for (const variable of variables) {
yield * getProblems({
context,
variable,
exportDeclarations,
program,
});
}
},
};
}
module.exports = {
create,
meta: {
type: 'suggestion',
docs: {
description: 'Prefer `export…from` when re-exporting.',
},
fixable: 'code',
messages,
},
};