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Diffstat (limited to 'tools/node_modules/eslint/lib/rules/no-unused-expressions.js')
-rw-r--r-- | tools/node_modules/eslint/lib/rules/no-unused-expressions.js | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/rules/no-unused-expressions.js b/tools/node_modules/eslint/lib/rules/no-unused-expressions.js new file mode 100644 index 0000000000..b4e1074d54 --- /dev/null +++ b/tools/node_modules/eslint/lib/rules/no-unused-expressions.js @@ -0,0 +1,126 @@ +/** + * @fileoverview Flag expressions in statement position that do not side effect + * @author Michael Ficarra + */ +"use strict"; + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +module.exports = { + meta: { + docs: { + description: "disallow unused expressions", + category: "Best Practices", + recommended: false + }, + + schema: [ + { + type: "object", + properties: { + allowShortCircuit: { + type: "boolean" + }, + allowTernary: { + type: "boolean" + }, + allowTaggedTemplates: { + type: "boolean" + } + }, + additionalProperties: false + } + ] + }, + + create(context) { + const config = context.options[0] || {}, + allowShortCircuit = config.allowShortCircuit || false, + allowTernary = config.allowTernary || false, + allowTaggedTemplates = config.allowTaggedTemplates || false; + + /** + * @param {ASTNode} node - any node + * @returns {boolean} whether the given node structurally represents a directive + */ + function looksLikeDirective(node) { + return node.type === "ExpressionStatement" && + node.expression.type === "Literal" && typeof node.expression.value === "string"; + } + + /** + * @param {Function} predicate - ([a] -> Boolean) the function used to make the determination + * @param {a[]} list - the input list + * @returns {a[]} the leading sequence of members in the given list that pass the given predicate + */ + function takeWhile(predicate, list) { + for (let i = 0; i < list.length; ++i) { + if (!predicate(list[i])) { + return list.slice(0, i); + } + } + return list.slice(); + } + + /** + * @param {ASTNode} node - a Program or BlockStatement node + * @returns {ASTNode[]} the leading sequence of directive nodes in the given node's body + */ + function directives(node) { + return takeWhile(looksLikeDirective, node.body); + } + + /** + * @param {ASTNode} node - any node + * @param {ASTNode[]} ancestors - the given node's ancestors + * @returns {boolean} whether the given node is considered a directive in its current position + */ + function isDirective(node, ancestors) { + const parent = ancestors[ancestors.length - 1], + grandparent = ancestors[ancestors.length - 2]; + + return (parent.type === "Program" || parent.type === "BlockStatement" && + (/Function/.test(grandparent.type))) && + directives(parent).indexOf(node) >= 0; + } + + /** + * Determines whether or not a given node is a valid expression. Recurses on short circuit eval and ternary nodes if enabled by flags. + * @param {ASTNode} node - any node + * @returns {boolean} whether the given node is a valid expression + */ + function isValidExpression(node) { + if (allowTernary) { + + // Recursive check for ternary and logical expressions + if (node.type === "ConditionalExpression") { + return isValidExpression(node.consequent) && isValidExpression(node.alternate); + } + } + + if (allowShortCircuit) { + if (node.type === "LogicalExpression") { + return isValidExpression(node.right); + } + } + + if (allowTaggedTemplates && node.type === "TaggedTemplateExpression") { + return true; + } + + return /^(?:Assignment|Call|New|Update|Yield|Await)Expression$/.test(node.type) || + (node.type === "UnaryExpression" && ["delete", "void"].indexOf(node.operator) >= 0); + } + + return { + ExpressionStatement(node) { + if (!isValidExpression(node.expression) && !isDirective(node, context.getAncestors())) { + context.report({ node, message: "Expected an assignment or function call and instead saw an expression." }); + } + } + }; + + } +}; |