From 4c50d85b423343ec67f1913749556e31d68aade7 Mon Sep 17 00:00:00 2001
From: Don Syme <dsyme@github.com>
Date: Tue, 3 Nov 2026 18:34:49 +0000
Subject: [PATCH] Dispatch fingerprint callbacks only to matching source lines

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 lib/entry-points.js                           | 11 +++--
 src/fingerprints.test.ts                      | 49 +++++++++++++++++++
 src/fingerprints.ts                           | 17 ++++---
 .../fingerprint-callback-dispatch.md          |  1 +
 4 files changed, 66 insertions(+), 12 deletions(-)
 create mode 100644 unreleased-change-notes/fingerprint-callback-dispatch.md

diff --git a/lib/entry-points.js b/lib/entry-points.js
index 0e179f3fc7..eb00bf4c38 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -187830,16 +187830,17 @@ async function addFingerprints(sarifLog, sourceRoot, logger2) {
         continue;
       }
       if (!callbacksByFile[filepath]) {
-        callbacksByFile[filepath] = [];
+        callbacksByFile[filepath] = /* @__PURE__ */ new Map();
       }
-      callbacksByFile[filepath].push(
-        locationUpdateCallback(result, primaryLocation, logger2)
-      );
+      const startLine = primaryLocation.physicalLocation.region.startLine;
+      const callbacks = callbacksByFile[filepath].get(startLine) ?? [];
+      callbacks.push(locationUpdateCallback(result, primaryLocation, logger2));
+      callbacksByFile[filepath].set(startLine, callbacks);
     }
   }
   for (const [filepath, callbacks] of Object.entries(callbacksByFile)) {
     const teeCallback = function(lineNumber, hashValue) {
-      for (const c of Object.values(callbacks)) {
+      for (const c of callbacks.get(lineNumber) ?? []) {
         c(lineNumber, hashValue);
       }
     };
diff --git a/src/fingerprints.test.ts b/src/fingerprints.test.ts
index 6b480a777f..8f2672612a 100644
--- a/src/fingerprints.test.ts
+++ b/src/fingerprints.test.ts
@@ -223,6 +223,55 @@ test("addFingerprints", async (t) => {
   );
 });
 
+test("addFingerprints dispatches to every result on the matching line", async (t) => {
+  await util.withTmpDir(async (tmpDir) => {
+    const filepath = path.join(tmpDir, "source.c");
+    fs.writeFileSync(filepath, "first\nsecond\nthird\n");
+    const hashes = new Map<number, string>();
+    await fingerprints.hash((line, hash) => hashes.set(line, hash), filepath);
+    const lines = [1, 2, 2, 3, 999];
+    const results: sarif.Result[] = lines.map((startLine) => ({
+      message: { text: "Finding" },
+      locations: [
+        {
+          physicalLocation: {
+            artifactLocation: { uri: "source.c" },
+            region: { startLine },
+          },
+        },
+      ],
+    }));
+    results[0].partialFingerprints = {
+      primaryLocationLineHash: "existing-fingerprint",
+    };
+    const logger = new RecordingLogger();
+    await fingerprints.addFingerprints(
+      {
+        runs: [{ tool: { driver: { name: "test" } }, results }],
+      },
+      tmpDir,
+      logger,
+    );
+
+    t.is(
+      results[0].partialFingerprints?.primaryLocationLineHash,
+      "existing-fingerprint",
+    );
+    t.true(
+      logger.hasMessage(
+        "existing inconsistent fingerprint value existing-fingerprint",
+      ),
+    );
+    for (const index of [1, 2, 3]) {
+      t.is(
+        results[index].partialFingerprints?.primaryLocationLineHash,
+        hashes.get(lines[index]),
+      );
+    }
+    t.is(results[4].partialFingerprints, undefined);
+  });
+});
+
 test("missingRegions", async (t) => {
   // Run an end-to-end test on a test file
   const input = JSON.parse(
diff --git a/src/fingerprints.ts b/src/fingerprints.ts
index 14cf30e63f..fb6e63922c 100644
--- a/src/fingerprints.ts
+++ b/src/fingerprints.ts
@@ -266,7 +266,9 @@ export async function addFingerprints(
   );
   // Gather together results for the same file and construct
   // callbacks to accept hashes for that file and update the location
-  const callbacksByFile: { [filename: string]: hashCallback[] } = {};
+  const callbacksByFile: {
+    [filename: string]: Map<number, hashCallback[]>;
+  } = {};
   for (const run of sarifLog.runs || []) {
     // We may need the list of artifacts to resolve against
     const artifacts = run.artifacts || [];
@@ -298,19 +300,20 @@ export async function addFingerprints(
         continue;
       }
       if (!callbacksByFile[filepath]) {
-        callbacksByFile[filepath] = [];
+        callbacksByFile[filepath] = new Map();
       }
-      callbacksByFile[filepath].push(
-        locationUpdateCallback(result, primaryLocation, logger),
-      );
+      const startLine = primaryLocation.physicalLocation.region.startLine;
+      const callbacks = callbacksByFile[filepath].get(startLine) ?? [];
+      callbacks.push(locationUpdateCallback(result, primaryLocation, logger));
+      callbacksByFile[filepath].set(startLine, callbacks);
     }
   }
 
   // Now hash each file that was found
   for (const [filepath, callbacks] of Object.entries(callbacksByFile)) {
-    // A callback that forwards the hash to all other callbacks for that file
+    // Forward each hash only to results on that line.
     const teeCallback = function (lineNumber: number, hashValue: string) {
-      for (const c of Object.values(callbacks)) {
+      for (const c of callbacks.get(lineNumber) ?? []) {
         c(lineNumber, hashValue);
       }
     };
diff --git a/unreleased-change-notes/fingerprint-callback-dispatch.md b/unreleased-change-notes/fingerprint-callback-dispatch.md
new file mode 100644
index 0000000000..57409469b7
--- /dev/null
+++ b/unreleased-change-notes/fingerprint-callback-dispatch.md
@@ -0,0 +1 @@
+- Improved SARIF fingerprint generation for source files with many results without changing the generated fingerprints.