bot: Assume lines outside the coverage record are uncoverable

It can happen for the last few lines of a file, if they are actually uncoverable.
For some reason, they are not considered by instrumentation.

Author: marco-c

bot/code_coverage_bot/phabricator.py

@@ -90,9 +90,12 @@ def _build_coverage_map(self, annotate, coverage_record):
             # The changeset when it was introduced.
             orig_changeset = data["node"]
 
-            if lineno < len(coverage_record):
-                key = (orig_changeset, orig_line)
-                coverage_map[key] = coverage_record[lineno]
+            key = (orig_changeset, orig_line)
+            # Assume lines outside the coverage record are uncoverable (that happens for the
+            # last few lines of a file, they are not considered by instrumentation).
+            coverage_map[key] = (
+                coverage_record[lineno] if lineno < len(coverage_record) else -1
+            )
 
         return coverage_map
 

bot/tests/test_phabricator.py

@@ -448,6 +448,37 @@ def test_backout_removed_file(mock_secrets, fake_hg_repo):
     }
 
 
+def test_coverable_last_lines(mock_secrets, mock_phabricator, fake_hg_repo):
+    hg, local, remote = fake_hg_repo
+
+    add_file(hg, local, "file", "1\n2\n3\n4\n5\n6\n7\n")
+    revision = commit(hg, 1)
+
+    hg.push(dest=bytes(remote, "ascii"))
+
+    copy_pushlog_database(remote, local)
+
+    phabricator = PhabricatorUploader(local, revision)
+    report = covdir_report(
+        {"source_files": [{"name": "file", "coverage": [None, 0, 1, 1, 1]}]}
+    )
+    results = phabricator.generate(report, changesets(local, revision))
+
+    assert results == {
+        revision: {
+            "revision_id": 1,
+            "paths": {
+                "file": {
+                    "coverage": "NUCCCNN",
+                    "lines_added": 4,
+                    "lines_covered": 3,
+                    "lines_unknown": 0,
+                }
+            },
+        }
+    }
+
+
 def test_third_party(mock_secrets, fake_hg_repo):
     hg, local, remote = fake_hg_repo