getPullRequestEditedDiffRanges: use GitHub API

src/analyze-action.ts

@@ -268,7 +268,7 @@ async function run() {
       pull_request &&
       (await setupDiffInformedQueryRun(
         pull_request.base.ref as string,
-        pull_request.head.ref as string,
+        pull_request.head.label as string,
         codeql,
         logger,
         features,

src/analyze.ts

@@ -7,6 +7,7 @@ import del from "del";
 import * as yaml from "js-yaml";
 
 import * as actionsUtil from "./actions-util";
+import { getApiClient } from "./api-client";
 import { setupCppAutobuild } from "./autobuild";
 import {
   CODEQL_VERSION_ANALYSIS_SUMMARY_V2,
@@ -17,7 +18,6 @@ import * as configUtils from "./config-utils";
 import { addDiagnostic, makeDiagnostic } from "./diagnostics";
 import { EnvVar } from "./environment";
 import { FeatureEnablement, Feature } from "./feature-flags";
-import * as gitUtils from "./git-utils";
 import { isScannedLanguage, Language } from "./languages";
 import { Logger, withGroupAsync } from "./logging";
 import { DatabaseCreationTimings, EventReport } from "./status-report";
@@ -240,7 +240,8 @@ async function finalizeDatabaseCreation(
  * Set up the diff-informed analysis feature.
  *
  * @param baseRef The base branch name, used for calculating the diff range.
- * @param headRef The head branch name, used for calculating the diff range.
+ * @param headLabel The label that uniquely identifies the head branch across
+ * repositories, used for calculating the diff range.
  * @param codeql
  * @param logger
  * @param features
@@ -249,7 +250,7 @@ async function finalizeDatabaseCreation(
  */
 export async function setupDiffInformedQueryRun(
   baseRef: string,
-  headRef: string,
+  headLabel: string,
   codeql: CodeQL,
   logger: Logger,
   features: FeatureEnablement,
@@ -262,7 +263,7 @@ export async function setupDiffInformedQueryRun(
     async () => {
       const diffRanges = await getPullRequestEditedDiffRanges(
         baseRef,
-        headRef,
+        headLabel,
         logger,
       );
       return writeDiffRangeDataExtensionPack(logger, diffRanges);
@@ -280,7 +281,8 @@ interface DiffThunkRange {
  * Return the file line ranges that were added or modified in the pull request.
  *
  * @param baseRef The base branch name, used for calculating the diff range.
- * @param headRef The head branch name, used for calculating the diff range.
+ * @param headLabel The label that uniquely identifies the head branch across
+ * repositories, used for calculating the diff range.
  * @param logger
  * @returns An array of tuples, where each tuple contains the absolute path of a
  * file, the start line and the end line (both 1-based and inclusive) of an
@@ -289,107 +291,61 @@ interface DiffThunkRange {
  */
 async function getPullRequestEditedDiffRanges(
   baseRef: string,
-  headRef: string,
+  headLabel: string,
   logger: Logger,
 ): Promise<DiffThunkRange[] | undefined> {
-  const checkoutPath = actionsUtil.getOptionalInput("checkout_path");
-  if (checkoutPath === undefined) {
-    return undefined;
-  }
-
-  // To compute the merge bases between the base branch and the PR topic branch,
-  // we need to fetch the commit graph from the branch heads to those merge
-  // babes. The following 6-step procedure does so while limiting the amount of
-  // history fetched.
-
-  // Step 1: Deepen from the PR merge commit to the base branch head and the PR
-  // topic branch head, so that the PR merge commit is no longer considered a
-  // grafted commit.
-  await gitUtils.deepenGitHistory();
-  // Step 2: Fetch the base branch shallow history. This step ensures that the
-  // base branch name is present in the local repository. Normally the base
-  // branch name would be added by Step 4. However, if the base branch head is
-  // an ancestor of the PR topic branch head, Step 4 would fail without doing
-  // anything, so we need to fetch the base branch explicitly.
-  await gitUtils.gitFetch(baseRef, ["--depth=1"]);
-  // Step 3: Fetch the PR topic branch history, stopping when we reach commits
-  // that are reachable from the base branch head.
-  await gitUtils.gitFetch(headRef, [`--shallow-exclude=${baseRef}`]);
-  // Step 4: Fetch the base branch history, stopping when we reach commits that
-  // are reachable from the PR topic branch head.
-  await gitUtils.gitFetch(baseRef, [`--shallow-exclude=${headRef}`]);
-  // Step 5: Repack the history to remove the shallow grafts that were added by
-  // the previous fetches. This step works around a bug that causes subsequent
-  // deepening fetches to fail with "fatal: error in object: unshallow <SHA>".
-  // See https://stackoverflow.com/q/63878612
-  await gitUtils.gitRepack(["-d"]);
-  // Step 6: Deepen the history so that we have the merge bases between the base
-  // branch and the PR topic branch.
-  await gitUtils.deepenGitHistory();
-
-  // To compute the exact same diff as GitHub would compute for the PR, we need
-  // to use the same merge base as GitHub. That is easy to do if there is only
-  // one merge base, which is by far the most common case. If there are multiple
-  // merge bases, we stop without producing a diff range.
-  const mergeBases = await gitUtils.getAllGitMergeBases([baseRef, headRef]);
-  logger.info(`Merge bases: ${mergeBases.join(", ")}`);
-  if (mergeBases.length !== 1) {
-    logger.info(
-      "Cannot compute diff range because baseRef and headRef " +
-        `have ${mergeBases.length} merge bases (instead of exactly 1).`,
-    );
-    return undefined;
-  }
-
-  const diffHunkHeaders = await gitUtils.getGitDiffHunkHeaders(
-    mergeBases[0],
-    headRef,
-  );
-  if (diffHunkHeaders === undefined) {
-    return undefined;
-  }
+  await getFileDiffsWithBasehead(baseRef, headLabel, logger);
+  return undefined;
+}
 
-  const results = new Array<DiffThunkRange>();
-
-  let changedFile = "";
-  for (const line of diffHunkHeaders) {
-    if (line.startsWith("+++ ")) {
-      const filePath = gitUtils.decodeGitFilePath(line.substring(4));
-      if (filePath.startsWith("b/")) {
-        // The file was edited: track all hunks in the file
-        changedFile = filePath.substring(2);
-      } else if (filePath === "/dev/null") {
-        // The file was deleted: skip all hunks in the file
-        changedFile = "";
-      } else {
-        logger.warning(`Failed to parse diff hunk header line: ${line}`);
-        return undefined;
-      }
-      continue;
-    }
-    if (line.startsWith("@@ ")) {
-      if (changedFile === "") continue;
+/**
+ * This interface is an abbreviated version of the file diff object returned by
+ * the GitHub API.
+ */
+interface FileDiff {
+  filename: string;
+  changes: number;
+  // A patch may be absent if the file is binary, if the file diff is too large,
+  // or if the file is unchanged.
+  patch?: string | undefined;
+}
 
-      const match = line.match(/^@@ -\d+(?:,\d+)? \+(\d+)(?:,(\d+))? @@/);
-      if (match === null) {
-        logger.warning(`Failed to parse diff hunk header line: ${line}`);
-        return undefined;
-      }
-      const startLine = parseInt(match[1], 10);
-      const numLines = parseInt(match[2], 10);
-      if (numLines === 0) {
-        // The hunk was a deletion: skip it
-        continue;
-      }
-      const endLine = startLine + (numLines || 1) - 1;
-      results.push({
-        path: path.join(checkoutPath, changedFile),
-        startLine,
-        endLine,
-      });
+async function getFileDiffsWithBasehead(
+  baseRef: string,
+  headLabel: string,
+  logger: Logger,
+): Promise<FileDiff[] | undefined> {
+  const ownerRepo = util.getRequiredEnvParam("GITHUB_REPOSITORY").split("/");
+  const owner = ownerRepo[0];
+  const repo = ownerRepo[1];
+  const basehead = `${baseRef}...${headLabel}`;
+  try {
+    const response = await getApiClient().rest.repos.compareCommitsWithBasehead(
+      {
+        owner,
+        repo,
+        basehead,
+        per_page: 1,
+      },
+    );
+    logger.debug(
+      `Response from compareCommitsWithBasehead(${basehead}):` +
+        `\n${JSON.stringify(response, null, 2)}`,
+    );
+    return response.data.files;
+  } catch (error: any) {
+    if (error.status) {
+      logger.warning(`Error retrieving diff ${basehead}: ${error.message}`);
+      logger.debug(
+        `Error running compareCommitsWithBasehead(${basehead}):` +
+          `\nRequest: ${JSON.stringify(error.request, null, 2)}` +
+          `\nError Response: ${JSON.stringify(error.response, null, 2)}`,
+      );
+      return undefined;
+    } else {
+      throw error;
     }
   }
-  return results;
 }
 
 /**