Chore: avoid mutating report descriptors in report-translator (#9189)

lib/report-translator.js

@@ -41,7 +41,7 @@ function normalizeMultiArgReportCall() {
 
     // If there is one argument, it is considered to be a new-style call already.
     if (arguments.length === 1) {
-        return Object.assign({}, arguments[0]);
+        return arguments[0];
     }
 
     // If the second argument is a string, the arguments are interpreted as [node, message, data, fix].
@@ -67,7 +67,7 @@ function normalizeMultiArgReportCall() {
 /**
  * Asserts that either a loc or a node was provided, and the node is valid if it was provided.
  * @param {MessageDescriptor} descriptor A descriptor to validate
- * @returns {MessageDescriptor} The same descriptor
+ * @returns {void}
  * @throws AssertionError if neither a node nor a loc was provided, or if the node is not an object
  */
 function assertValidNodeInfo(descriptor) {
@@ -76,46 +76,39 @@ function assertValidNodeInfo(descriptor) {
     } else {
         assert(descriptor.loc, "Node must be provided when reporting error if location is not provided");
     }
-
-    return descriptor;
 }
 
 /**
  * Normalizes a MessageDescriptor to always have a `loc` with `start` and `end` properties
- * @param {MessageDescriptor} descriptor A descriptor for the report from a rule. This descriptor may be mutated
- * by this function.
- * @returns {MessageDescriptor} The updated MessageDescriptor that infers the `start` and `end` properties from
- * the `node` of the original descriptor, or infers the `start` from the `loc` of the original descriptor.
+ * @param {MessageDescriptor} descriptor A descriptor for the report from a rule.
+ * @returns {{start: Location, end: (Location|null)}} An updated location that infers the `start` and `end` properties
+ * from the `node` of the original descriptor, or infers the `start` from the `loc` of the original descriptor.
  */
 function normalizeReportLoc(descriptor) {
     if (descriptor.loc) {
         if (descriptor.loc.start) {
-            return descriptor;
+            return descriptor.loc;
         }
-        return Object.assign(descriptor, { loc: { start: descriptor.loc, end: null } });
+        return { start: descriptor.loc, end: null };
     }
-
-    return Object.assign(descriptor, { loc: descriptor.node.loc });
+    return descriptor.node.loc;
 }
 
 /**
  * Interpolates data placeholders in report messages
- * @param {MessageDescriptor} descriptor The report message descriptor. This descriptor may be mutated
- * by this function.
- * @returns {MessageDescriptor} An new descriptor with a message containing the interpolated data
+ * @param {MessageDescriptor} descriptor The report message descriptor.
+ * @returns {string} The interpolated message for the descriptor
  */
 function normalizeMessagePlaceholders(descriptor) {
     if (!descriptor.data) {
-        return descriptor;
+        return descriptor.message;
     }
-    return Object.assign(descriptor, {
-        message: descriptor.message.replace(/\{\{\s*([^{}]+?)\s*\}\}/g, (fullMatch, term) => {
-            if (term in descriptor.data) {
-                return descriptor.data[term];
-            }
-
-            return fullMatch;
-        })
+    return descriptor.message.replace(/\{\{\s*([^{}]+?)\s*\}\}/g, (fullMatch, term) => {
+        if (term in descriptor.data) {
+            return descriptor.data[term];
+        }
+
+        return fullMatch;
     });
 }
 
@@ -134,7 +127,7 @@ function compareFixesByRange(a, b) {
  * Merges the given fixes array into one.
  * @param {Fix[]} fixes The fixes to merge.
  * @param {SourceCode} sourceCode The source code object to get the text between fixes.
- * @returns {void}
+ * @returns {{text: string, range: [number, number]}} The merged fixes
  */
 function mergeFixes(fixes, sourceCode) {
     if (fixes.length === 0) {
@@ -169,31 +162,36 @@ function mergeFixes(fixes, sourceCode) {
 /**
  * Gets one fix object from the given descriptor.
  * If the descriptor retrieves multiple fixes, this merges those to one.
- * @param {MessageDescriptor} descriptor The report descriptor. This descriptor may be mutated
- * by this function.
+ * @param {MessageDescriptor} descriptor The report descriptor.
  * @param {SourceCode} sourceCode The source code object to get text between fixes.
- * @returns {MessageDescriptor} The updated descriptor.
+ * @returns {({text: string, range: [number, number]}|null)} The fix for the descriptor
  */
 function normalizeFixes(descriptor, sourceCode) {
     if (typeof descriptor.fix !== "function") {
-        return Object.assign(descriptor, { fix: null });
+        return null;
     }
 
     // @type {null | Fix | Fix[] | IterableIterator<Fix>}
     const fix = descriptor.fix(ruleFixer);
 
     // Merge to one.
     if (fix && Symbol.iterator in fix) {
-        return Object.assign(descriptor, { fix: mergeFixes(Array.from(fix), sourceCode) });
+        return mergeFixes(Array.from(fix), sourceCode);
     }
-    return Object.assign(descriptor, { fix });
+    return fix;
 }
 
 /**
  * Creates information about the report from a descriptor
- * @param {MessageDescriptor} descriptor The message descriptor
- * @param {string} ruleId The rule ID of the problem
- * @param {(0|1|2)} severity The severity of the problem
+ * @param {{
+ *     ruleId: string,
+ *     severity: (0|1|2),
+ *     node: (ASTNode|null),
+ *     message: string,
+ *     loc: {start: SourceLocation, end: (SourceLocation|null)},
+ *     fix: ({text: string, range: [number, number]}|null),
+ *     sourceLines: string[]
+ * }} options Information about the problem
  * @returns {function(...args): {
  *      ruleId: string,
  *      severity: (0|1|2),
@@ -207,23 +205,24 @@ function normalizeFixes(descriptor, sourceCode) {
  *      fix: ({text: string, range: [number, number]}|null)
  * }} Information about the report
  */
-function createProblemFromDescriptor(descriptor, ruleId, severity) {
+function createProblem(options) {
     const problem = {
-        ruleId,
-        severity,
-        message: descriptor.message,
-        line: descriptor.loc.start.line,
-        column: descriptor.loc.start.column + 1,
-        nodeType: descriptor.node && descriptor.node.type || null
+        ruleId: options.ruleId,
+        severity: options.severity,
+        message: options.message,
+        line: options.loc.start.line,
+        column: options.loc.start.column + 1,
+        nodeType: options.node && options.node.type || null,
+        source: options.sourceLines[options.loc.start.line - 1] || ""
     };
 
-    if (descriptor.loc.end) {
-        problem.endLine = descriptor.loc.end.line;
-        problem.endColumn = descriptor.loc.end.column + 1;
+    if (options.loc.end) {
+        problem.endLine = options.loc.end.line;
+        problem.endColumn = options.loc.end.column + 1;
     }
 
-    if (descriptor.fix) {
-        problem.fix = descriptor.fix;
+    if (options.fix) {
+        problem.fix = options.fix;
     }
 
     return problem;
@@ -261,14 +260,15 @@ module.exports = function createReportTranslator(metadata) {
         const descriptor = normalizeMultiArgReportCall.apply(null, arguments);
 
         assertValidNodeInfo(descriptor);
-        normalizeReportLoc(descriptor);
-        normalizeMessagePlaceholders(descriptor);
-        normalizeFixes(descriptor, metadata.sourceCode);
-
-        const problem = createProblemFromDescriptor(descriptor, metadata.ruleId, metadata.severity);
-
-        problem.source = metadata.sourceCode.lines[problem.line - 1] || "";
 
-        return problem;
+        return createProblem({
+            ruleId: metadata.ruleId,
+            severity: metadata.severity,
+            node: descriptor.node,
+            message: normalizeMessagePlaceholders(descriptor),
+            loc: normalizeReportLoc(descriptor),
+            fix: normalizeFixes(descriptor, metadata.sourceCode),
+            sourceLines: metadata.sourceCode.lines
+        });
     };
 };