Fix TypeError, division by zero, and KeyError in leaderboard calculations

[Copilot]

Addresses runtime errors in _build_index_context() that occur when processing leaderboard entries with missing slugs, zero completed issues, or unmapped contributors.

Changes

• Leaderboard filtering: Use walrus operator to check slug is not None before membership test, preventing TypeError when external contributors have no slug

  # Before: fails when slug is None
  entry for entry in leaderboard_entries if entry.get("slug") in apollos_team_slugs
  
  # After: safely handles None
  if (slug := entry.get("slug")) is not None and slug in apollos_team_slugs

• Division by zero: Calculate total_completed_issues once and guard against zero denominator in priority_percentage calculation

  "priority_percentage": int(
      len(completed_priority_bugs) / total_completed_issues * 100
  ) if total_completed_issues else 0,

• KeyError prevention: Replace direct display_name_overrides[slug] access with .get(slug, fallback) in 5 locations:

  • Issue assignee processing (line 262)
  • PR reviewer scoring (line 300)
  • PR author scoring (line 331)
  • Cycle lead points (line 360)
  • Cycle member points (line 393)

  Each uses appropriate fallback: display_name for assignees, format_display_name(username) for GitHub users and project participants.

Original prompt

Please apply the following diffs and create a pull request.
Once the PR is ready, give it a title based on the messages of the fixes being applied.

[{"message":"The filter condition will fail when entry.get(\"slug\") returns None (for external contributors). Using 'in' with None will raise a TypeError. Should check if slug is not None before the membership test.","fixFiles":[{"filePath":"app.py","diff":"diff --git a/app.py b/app.py\n--- a/app.py\n+++ b/app.py\n@@ -433,7 +433,9 @@\n     )\n \n     leaderboard_entries = [\n-        entry for entry in leaderboard_entries if entry.get(\"slug\") in apollos_team_slugs\n+        entry\n+        for entry in leaderboard_entries\n+        if (slug := entry.get(\"slug\")) is not None and slug in apollos_team_slugs\n     ]\n \n     leaderboard_entries.sort(key=lambda entry: entry[\"score\"], reverse=True)\n"}]},{"message":"Division by zero error will occur if the total number of completed issues is zero. Should add a check to handle the case where the denominator is zero.","fixFiles":[{"filePath":"app.py","diff":"diff --git a/app.py b/app.py\n--- a/app.py\n+++ b/app.py\n@@ -438,6 +438,10 @@\n \n     leaderboard_entries.sort(key=lambda entry: entry[\"score\"], reverse=True)\n \n+    total_completed_issues = len(\n+        completed_bugs + completed_new_features + completed_technical_changes\n+    )\n+\n     return {\n         \"days\": days,\n         \"priority_issues\": sorted(\n@@ -445,14 +449,8 @@\n         ),\n         \"issue_count\": len(created_priority_bugs),\n         \"priority_percentage\": int(\n-            len(completed_priority_bugs)\n-            / len(\n-                completed_bugs\n-                + completed_new_features\n-                + completed_technical_changes\n-            )\n-            * 100\n-        ),\n+            len(completed_priority_bugs) / total_completed_issues * 100\n+        ) if total_completed_issues else 0,\n         \"leaderboard_entries\": leaderboard_entries,\n         \"all_issues\": created_priority_bugs + open_priority_bugs,\n         \"issues_by_platform\": by_platform(created_priority_bugs),\n"}]},{"message":"Potential KeyError if slug is not in display_name_overrides dictionary. The code assumes every slug has a corresponding entry in display_name_overrides, but this might not always be true.","fixFiles":[{"filePath":"app.py","diff":"diff --git a/app.py b/app.py\n--- a/app.py\n+++ b/app.py\n@@ -259,7 +259,10 @@\n         category_key = PRIORITY_BREAKDOWN_KEYS.get(priority)\n         if slug:\n             scores_by_slug[slug] = scores_by_slug.get(slug, 0) + points\n-            names_by_slug.setdefault(slug, display_name or display_name_overrides[slug])\n+            names_by_slug.setdefault(\n+                slug,\n+                display_name or display_name_overrides.get(slug, display_name),\n+            )\n             if category_key:\n                 record_breakdown(\n                     points_breakdown_by_slug,\n"}]},{"message":"Potential KeyError if slug is not in display_name_overrides dictionary. Should use .get() method with a fallback value instead of direct dictionary access.","fixFiles":[{"filePath":"app.py","diff":"diff --git a/app.py b/app.py\n--- a/app.py\n+++ b/app.py\n@@ -294,7 +294,7 @@\n         slug = github_to_slug.get(normalize_identity(reviewer))\n         if slug:\n             scores_by_slug[slug] = scores_by_slug.get(slug, 0) + review_points\n-            names_by_slug.setdefault(slug, display_name_overrides[slug])\n+            names_by_slug.setdefault(slug, display_name_overrides.get(slug))\n             record_breakdown(\n                 points_breakdown_by_slug,\n                 count_breakdown_by_slug,\n"}]},{"message":"Potential KeyError if slug is not in display_name_overrides dictionary. Should use .get() method with a fallback value instead of direct dictionary access.","fixFiles":[{"filePath":"app.py","diff":"diff --git a/app.py b/app.py\n--- a/app.py\n+++ b/app.py\n@@ -294,7 +294,7 @@\n         slug = github_to_slug.get(normalize_identity(reviewer))\n         if slug:\n             scores_by_slug[slug] = scores_by_slug.get(slug, 0) + review_points\n-            names_by_slug.setdefault(slug, display_name_overrides[slug])\n+            names_by_slug.setdefault(slug, display_name_overrides.get(slug, format_display_name(reviewer)))\n             record_breakdown(\n                 points_breakdown_by_slug,\n                 count_breakdown_by_slug,\n@@ -325,7 +325,7 @@\n         slug = github_to_slug.get(normalize_identity(author))\n         if slug:\n             scores_by_slug[slug] = scores_by_slug.get(slug, 0) + pr_points\n-            names_by_slug.setdefault(slug, display_name_overrides[slug])\n+            names_by_slug.setdefault(slug, display_name_overrides.get(slug, format_display_name(author)))\n             record_breakdown(\n                 points_breakdown_by_slug,\n                 count_breakdown_by_slug,\n@@ -354,7 +354,7 @@\n     ...

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