fix(trend): count repeated fingerprints as a multiset (#97)

src/trend.test.ts

@@ -68,6 +68,32 @@ describe("computeTrend", () => {
 		expect(trend.fixed?.[0]).toMatchObject({ rule: "old", file: "src/a.ts" });
 	});
 
+	it("counts repeated fingerprints as a multiset: fixing one of two identical findings reports one fixed", () => {
+		const dir = mkdtempSync(join(tmpdir(), "vcqa-trend-"));
+		const dup = { severity: "warning" as const, rule: "no-any", message: "Avoid any", file: "src/a.ts" };
+		const prev = makeReport(80, [{ name: "types", score: 80, issues: 0 }]);
+		prev.checks[0].issues = [
+			{ ...dup, line: 3 },
+			{ ...dup, line: 9 },
+		];
+		writeFileSync(join(dir, "report.json"), JSON.stringify(prev));
+
+		const curr = makeReport(81, [{ name: "types", score: 81, issues: 0 }]);
+		curr.checks[0].issues = [{ ...dup, line: 3 }];
+
+		const trend = computeTrend(curr, dir)!;
+		expect(trend.fixedIssues).toBe(1);
+		expect(trend.newIssues).toBe(0);
+		expect(trend.fixed).toHaveLength(1);
+		expect(trend.fixed?.[0]).toMatchObject({ rule: "no-any", file: "src/a.ts" });
+
+		const back = mkdtempSync(join(tmpdir(), "vcqa-trend-"));
+		writeFileSync(join(back, "report.json"), JSON.stringify(curr));
+		const reverse = computeTrend(prev, back)!;
+		expect(reverse.newIssues).toBe(1);
+		expect(reverse.fixedIssues).toBe(0);
+	});
+
 	it("detects regressions", () => {
 		const dir = mkdtempSync(join(tmpdir(), "vcqa-trend-"));
 		const prev = makeReport(90, [{ name: "lint", score: 90, issues: 1 }]);

src/trend.ts

@@ -42,27 +42,41 @@ export function computeTrend(report: VibeReport, outputDir: string): TrendDelta
 		});
 	}
 
-	const prevIssueMap = issueMap(prev);
-	const currIssueMap = issueMap(report);
-	const introduced = [...currIssueMap.entries()].filter(([fp]) => !prevIssueMap.has(fp)).map(([, issue]) => issue);
-	const fixed = [...prevIssueMap.entries()].filter(([fp]) => !currIssueMap.has(fp)).map(([, issue]) => issue);
+	const prevIssues = issueMultiset(prev);
+	const currIssues = issueMultiset(report);
+	const introduced = surplus(currIssues, prevIssues);
+	const fixed = surplus(prevIssues, currIssues);
 	const newIssues = introduced.length;
 	const fixedIssues = fixed.length;
 
 	return { scoreDelta, checkDeltas, newIssues, fixedIssues, introduced, fixed, prevTimestamp: prev.timestamp };
 }
 
-function issueMap(report: VibeReport): Map<string, IssueSnapshot> {
-	const out = new Map<string, IssueSnapshot>();
+/** Group issues by fingerprint, keeping every occurrence (a multiset, as in delta.ts). */
+function issueMultiset(report: VibeReport): Map<string, IssueSnapshot[]> {
+	const out = new Map<string, IssueSnapshot[]>();
 	for (const check of report.checks) {
 		for (const issue of check.issues) {
 			const fp = readIssueFingerprint(check.name, issue);
-			out.set(fp, issueSnapshot(check.name, issue));
+			const list = out.get(fp);
+			const snap = issueSnapshot(check.name, issue);
+			if (list) list.push(snap);
+			else out.set(fp, [snap]);
 		}
 	}
 	return out;
 }
 
+/** Occurrences in `a` beyond the count of the same fingerprint in `b`. */
+function surplus(a: Map<string, IssueSnapshot[]>, b: Map<string, IssueSnapshot[]>): IssueSnapshot[] {
+	const out: IssueSnapshot[] = [];
+	for (const [fp, list] of a) {
+		const other = b.get(fp)?.length ?? 0;
+		if (list.length > other) out.push(...list.slice(other));
+	}
+	return out;
+}
+
 /** Render trend delta as terminal-friendly string with sparkline. */
 export function formatTrend(trend: TrendDelta, historyScores?: number[]): string {
 	const arrow = trend.scoreDelta > 0 ? "\u2191" : trend.scoreDelta < 0 ? "\u2193" : "=";