Implement code coverage for the SDK

[iand675]

TL;DR

Added code coverage generation for the Temporal SDK Haskell packages.

What changed?

• Added a new Nix overlay (nix/overlays/haskell/coverage.nix) that enables code coverage for the main temporal-sdk package while disabling Haddock documentation generation to speed up builds
• Created a new package definition (nix/packages/coverage.nix) that:
  • Builds coverage reports for the SDK
  • Copies HTML coverage reports and .tix files to the output
  • Provides convenience scripts to view and display coverage information
• Updated flake.nix to expose coverage packages for each GHC version in the Nix flake outputs

How to test?

1. Build the coverage package for a specific GHC version:

   nix build .#coverage-ghc94
   

2. View the coverage report:

   ./result/bin/view-coverage
   

3. Show the text coverage summary:

   ./result/bin/show-coverage-report
   

[iand675]

• Implement code coverage for the SDK #245 👈 (View in Graphite)
• main

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[github-actions]

📊 Code Coverage Report

Current PR Coverage

Overall Coverage: 🟠 58.3%

• 10162 / 17439 expressions covered

Overall Summary

Category	Coverage
Top-level definitions	793/2604 🔴 30.5%
Alternatives	27/57 🟠 47.4%
Expressions	9094/14355 🟡 63.4%
Local definitions	228/366 🟡 62.3%
Other	20/57 🔴 35.1%

Coverage by Module

Module	Coverage	Top-level	Alternatives	Expressions	Local
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.TH.Internal	🔴 0.0%	0/15 🔴 0.0%	0/2 🔴 0.0%	0/135 🔴 0.0%	0/2 🔴 0.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.TH	🔴 8.2%	1/21 🔴 4.8%	0/16 🔴 0.0%	41/460 🔴 8.9%	3/36 🔴 8.3%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.SearchAttributes	🔴 15.6%	12/101 🔴 11.9%	N/A	19/92 🔴 20.7%	0/6 🔴 0.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Common	🔴 16.1%	50/637 🔴 7.8%	1/1 🟢 100.0%	78/170 🟠 45.9%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Data.EvalRecord	🔴 21.0%	12/71 🔴 16.9%	N/A	68/308 🔴 22.1%	2/12 🔴 16.7%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Worker.Types	🔴 25.0%	9/35 🔴 25.7%	N/A	9/37 🔴 24.3%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Client.TestService	🔴 32.0%	7/16 🟠 43.8%	1/1 🟢 100.0%	43/139 🔴 30.9%	3/12 🔴 25.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Activity.Definition	🔴 35.1%	22/57 🔴 38.6%	N/A	24/74 🔴 32.4%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Payload	🔴 35.4%	38/125 🔴 30.4%	0/5 🔴 0.0%	162/438 🔴 37.0%	2/4 🟠 50.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Update	🟠 40.0%	1/3 🔴 33.3%	N/A	1/2 🟠 50.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Signal	🟠 40.0%	1/3 🔴 33.3%	N/A	1/2 🟠 50.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Query	🟠 40.0%	1/3 🔴 33.3%	N/A	1/2 🟠 50.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.TH.Classes	🟠 40.0%	10/27 🔴 37.0%	N/A	28/68 🟠 41.2%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Definition	🟠 41.7%	8/20 🟠 40.0%	N/A	32/76 🟠 42.1%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Types	🟠 45.3%	49/179 🔴 27.4%	N/A	81/108 🟡 75.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Bundle	🟠 45.5%	9/25 🔴 36.0%	N/A	91/199 🟠 45.7%	10/18 🟠 55.6%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Activity.Types	🟠 47.4%	9/20 🟠 45.0%	N/A	9/18 🟠 50.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Unsafe.Handle	🟠 49.4%	5/8 🟡 62.5%	N/A	72/148 🟠 48.6%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Coroutine	🟠 49.7%	12/23 🟠 52.2%	N/A	65/132 🟠 49.2%	3/6 🟠 50.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.WorkflowInstance	🟠 50.0%	1/1 🟢 100.0%	N/A	1/3 🔴 33.3%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.EphemeralServer	🟠 50.0%	4/13 🔴 30.8%	N/A	64/122 🟠 52.5%	0/1 🔴 0.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Common.Async	🟠 50.0%	1/2 🟠 50.0%	N/A	10/20 🟠 50.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Exception	🟠 52.0%	84/291 🔴 28.9%	2/3 🟡 66.7%	301/455 🟡 66.2%	5/5 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Testing.MockActivityEnvironment	🟠 53.4%	7/14 🟠 50.0%	N/A	43/84 🟠 51.2%	5/5 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Operator	🟠 55.6%	3/12 🔴 25.0%	1/1 🟢 100.0%	53/92 🟠 57.6%	2/2 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow	🟠 58.2%	38/104 🔴 36.5%	2/3 🟡 66.7%	1237/2085 🟠 59.3%	31/56 🟠 55.4%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Worker	🟠 59.1%	42/111 🔴 37.8%	1/1 🟢 100.0%	601/997 🟡 60.3%	34/39 🟢 87.2%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Internal.Monad	🟡 60.6%	135/254 🟠 53.1%	1/3 🔴 33.3%	613/976 🟡 62.8%	2/3 🟡 66.7%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Client.Types	🟡 65.5%	49/104 🟠 47.1%	N/A	124/159 🟡 78.0%	0/1 🔴 0.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Interceptor	🟡 67.6%	15/33 🟠 45.5%	N/A	56/72 🟡 77.8%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Activity	🟡 69.8%	3/6 🟠 50.0%	N/A	84/120 🟡 70.0%	3/3 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Duration	🟡 70.9%	27/64 🟠 42.2%	6/7 🟢 85.7%	213/274 🟡 77.7%	6/9 🟡 66.7%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.WorkflowInstance	🟡 71.2%	18/22 🟢 81.8%	2/2 🟢 100.0%	1258/1767 🟡 71.2%	29/42 🟡 69.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Contrib.OpenTelemetry	🟡 73.6%	3/7 🟠 42.9%	N/A	512/694 🟡 73.8%	12/15 🟢 80.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Internal.Instance	🟡 74.7%	6/8 🟡 75.0%	N/A	124/166 🟡 74.7%	6/8 🟡 75.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Client	🟡 76.2%	34/76 🟠 44.7%	5/7 🟡 71.4%	1455/1879 🟡 77.4%	26/32 🟢 81.2%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Common.Logging	🟢 81.0%	11/14 🟡 78.6%	1/1 🟢 100.0%	87/106 🟢 82.1%	3/4 🟡 75.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Testing.Assertions	🟢 81.1%	6/11 🟠 54.5%	N/A	24/26 🟢 92.3%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Activity.Worker	🟢 81.4%	25/36 🟡 69.4%	N/A	450/550 🟢 81.8%	10/10 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Worker	🟢 84.7%	15/22 🟡 68.2%	1/1 🟢 100.0%	630/740 🟢 85.1%	22/26 🟢 84.6%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Eval	🟢 91.1%	4/4 🟢 100.0%	3/3 🟢 100.0%	300/329 🟢 91.2%	9/9 🟢 100.0%
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.SearchAttributes.Internal	🟢 93.3%	5/5 🟢 100.0%	N/A	23/25 🟢 92.0%	N/A
temporal-sdk-2025.10.1.0-KbLX5CyBDl95aLVKKsIYt0/Temporal.Workflow.Unsafe	🟢 100.0%	1/1 🟢 100.0%	N/A	6/6 🟢 100.0%	N/A

---

🟢 ≥80% 🟡 ≥60% 🟠 ≥40% 🔴 <40%