bug: finally block in async function indicates incorrect missing block coverage

[bcoe]

Observed Behavior

The following code:

async function abc() {
  try {
    return 'abc';
  } finally {
    console.log('in finally');
  } // this is a covered line but uncovered branch
}

abc()

Ends up having the following coverage output:

{
          "functionName": "abc",
          "ranges": [
            {
              "startOffset": 0,
              "endOffset": 146,
              "count": 1
            },
            {
              "startOffset": 97,
              "endOffset": 145,
              "count": 0
            }
          ],
          "isBlockCoverage": true
        }
}

This indicates that the following characters were tracked as an uncovered block:

// this is a covered line but uncovered branch\n

Expected behavior

Coverage should be 100% in the above example.

[bcoe]

I have created a tracking issue on v8 here:

https://bugs.chromium.org/p/v8/issues/detail?id=10628

[evocateur]

I'm not sure if it's related, but I think I hit this? I happened to be on c8 v7.4.0 when I encountered the failure in CI, but it reproduces in v7.5.0 when run on node v12.20.1.

The tests pass, it's just the mysterious coverage gap on an async function that fails in node v12. v14 is fine.

dendrochronologist/cli@edd0aaf "fixes" it by ignoring the missed line. Not ideal, long-term.

However, if I avoid using the async keyword, it passes again:

diff --git a/src/api.ts b/src/api.ts
index 99472c5..69c22ef 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -9,7 +9,7 @@ interface RunOptions extends Partial<ParsedConfig> {
   logger?: MinimalLogger;
 }
 
-export async function run({
+export function run({
   logger = processLogger(),
   ...options
 }: RunOptions): Promise<Node> {
@@ -22,8 +22,5 @@ export async function run({
   const arb = new Arborist({
     path: cwd,
   });
-  const tree = await arb.loadVirtual().catch(() => arb.loadActual());
-
-  return tree;
-  /* c8 ignore next */
+  return arb.loadVirtual().catch(() => arb.loadActual());
 }

I validated this locally with

volta run --node 12 npm test