feat(FN-4315): complete Step 2 — add programmatic survival checks

Fusion-Task-Id: FN-4315
Fusion-Task-Lineage: 2646fd86-e525-4b62-a041-616fa7789e84

packages/engine/src/merger-audit-recovery.ts

@@ -0,0 +1,192 @@
+import { exec } from "node:child_process";
+import { promisify } from "node:util";
+
+import type {
+  SquashAuditDuplicateSubjectFinding,
+  SquashAuditTouchedFileOverlapFinding,
+} from "./merger-squash-audit.js";
+import type { Logger } from "./logger.js";
+
+const execAsync = promisify(exec);
+const DEFAULT_TIMEOUT_MS = 30_000;
+const MAX_BUFFER = 10 * 1024 * 1024;
+const NOISE_LINE_RE = /^[\s{}()\[\];,]*$/;
+
+export interface ContributionSurvivalResult {
+  file: string;
+  mainCommitSha: string;
+  addedLineCount: number;
+  missingLineCount: number;
+  survived: boolean;
+  sampleMissingLines: string[];
+}
+
+export interface SurvivalReport {
+  allSurvived: boolean;
+  perCommit: ContributionSurvivalResult[];
+}
+
+export async function checkContributionSurvival(opts: {
+  rootDir: string;
+  finding: SquashAuditTouchedFileOverlapFinding | SquashAuditDuplicateSubjectFinding;
+  headSha: string;
+  mergerLog: Logger;
+  timeoutMs?: number;
+}): Promise<SurvivalReport> {
+  const timeoutMs = opts.timeoutMs ?? DEFAULT_TIMEOUT_MS;
+  const checks: Array<{ file: string; mainCommitSha: string }> = [];
+
+  if (opts.finding.type === "touched-file-overlap") {
+    for (const commit of opts.finding.recentMainCommits) {
+      checks.push({ file: opts.finding.file, mainCommitSha: commit.sha });
+    }
+  } else {
+    const commitShas = await resolveSubjectCommits(opts.rootDir, opts.finding.subject, timeoutMs, opts.mergerLog);
+    for (const commitSha of commitShas) {
+      const files = await listCommitFiles(opts.rootDir, commitSha, timeoutMs, opts.mergerLog);
+      for (const file of files) {
+        checks.push({ file, mainCommitSha: commitSha });
+      }
+    }
+  }
+
+  if (checks.length === 0) {
+    return { allSurvived: false, perCommit: [] };
+  }
+
+  const perCommit: ContributionSurvivalResult[] = [];
+  for (const check of checks) {
+    perCommit.push(await evaluateFileContribution({ ...opts, ...check, timeoutMs }));
+  }
+
+  return {
+    allSurvived: perCommit.length > 0 && perCommit.every((item) => item.survived),
+    perCommit,
+  };
+}
+
+async function evaluateFileContribution(opts: {
+  rootDir: string;
+  file: string;
+  mainCommitSha: string;
+  headSha: string;
+  mergerLog: Logger;
+  timeoutMs: number;
+}): Promise<ContributionSurvivalResult> {
+  try {
+    const parentSha = (await runGit(opts.rootDir, `git rev-parse ${quoteArg(`${opts.mainCommitSha}^`)}`, opts.timeoutMs)).trim();
+    const postContent = await gitShowFile(opts.rootDir, opts.mainCommitSha, opts.file, opts.timeoutMs, opts.mergerLog);
+    const preContent = await gitShowFile(opts.rootDir, parentSha, opts.file, opts.timeoutMs, opts.mergerLog);
+    const headContent = await gitShowFile(opts.rootDir, opts.headSha, opts.file, opts.timeoutMs, opts.mergerLog);
+
+    const addedLines = diffAddedNormalized(preContent, postContent);
+    const headSet = new Set(normalizeLines(headContent));
+    const missing = addedLines.filter((line) => !headSet.has(line));
+
+    const survived = addedLines.length === 0
+      ? true
+      : missing.length / addedLines.length <= 0.05;
+
+    return {
+      file: opts.file,
+      mainCommitSha: opts.mainCommitSha,
+      addedLineCount: addedLines.length,
+      missingLineCount: missing.length,
+      survived,
+      sampleMissingLines: missing.slice(0, 5),
+    };
+  } catch (error) {
+    opts.mergerLog.warn(
+      `audit recovery: failed survival check for ${opts.mainCommitSha}:${opts.file} — ${error instanceof Error ? error.message : String(error)}`,
+    );
+    return {
+      file: opts.file,
+      mainCommitSha: opts.mainCommitSha,
+      addedLineCount: 0,
+      missingLineCount: 0,
+      survived: false,
+      sampleMissingLines: [],
+    };
+  }
+}
+
+async function resolveSubjectCommits(
+  rootDir: string,
+  subject: string,
+  timeoutMs: number,
+  mergerLog: Logger,
+): Promise<string[]> {
+  try {
+    const output = await runGit(rootDir, "git log --format=%H%x09%s -n 300", timeoutMs);
+    return output
+      .split("\n")
+      .map((line) => line.trim())
+      .filter(Boolean)
+      .map((line) => {
+        const [sha, ...parts] = line.split("\t");
+        return { sha, subject: parts.join("\t") };
+      })
+      .filter((entry) => entry.subject === subject)
+      .map((entry) => entry.sha);
+  } catch (error) {
+    mergerLog.warn(`audit recovery: failed resolving commits for subject \"${subject}\" — ${error instanceof Error ? error.message : String(error)}`);
+    return [];
+  }
+}
+
+async function listCommitFiles(rootDir: string, commitSha: string, timeoutMs: number, mergerLog: Logger): Promise<string[]> {
+  try {
+    const output = await runGit(rootDir, `git show --name-only --pretty=format: ${quoteArg(commitSha)}`, timeoutMs);
+    return output.split("\n").map((line) => line.trim()).filter(Boolean);
+  } catch (error) {
+    mergerLog.warn(`audit recovery: failed listing files for commit ${commitSha} — ${error instanceof Error ? error.message : String(error)}`);
+    return [];
+  }
+}
+
+async function gitShowFile(
+  rootDir: string,
+  commitSha: string,
+  file: string,
+  timeoutMs: number,
+  mergerLog: Logger,
+): Promise<string> {
+  try {
+    return await runGit(rootDir, `git show ${quoteArg(`${commitSha}:${file}`)}`, timeoutMs);
+  } catch (error) {
+    const message = error instanceof Error ? error.message : String(error);
+    if (message.includes("exists on disk") || message.includes("does not exist") || message.includes("Path '") || message.includes("fatal:")) {
+      mergerLog.warn(`audit recovery: unable to read ${commitSha}:${file} (${message})`);
+      return "";
+    }
+    throw error;
+  }
+}
+
+function diffAddedNormalized(before: string, after: string): string[] {
+  const beforeSet = new Set(normalizeLines(before));
+  const afterLines = normalizeLines(after);
+  return [...new Set(afterLines.filter((line) => !beforeSet.has(line)))];
+}
+
+function normalizeLines(content: string): string[] {
+  return content
+    .split("\n")
+    .map((line) => line.trimEnd().trim())
+    .filter((line) => line.length > 0)
+    .filter((line) => !NOISE_LINE_RE.test(line));
+}
+
+async function runGit(rootDir: string, command: string, timeoutMs: number): Promise<string> {
+  const { stdout } = await execAsync(command, {
+    cwd: rootDir,
+    timeout: timeoutMs,
+    maxBuffer: MAX_BUFFER,
+    encoding: "utf-8",
+  });
+  return stdout;
+}
+
+function quoteArg(value: string): string {
+  return `'${value.replace(/'/g, "'\\''")}'`;
+}