ci: add code coverage workflow with llvm-cov (#246)

# Rationale for this change

Coverage reports help a lot with code quality and review.

# What changes are included in this PR?

* Added llvm-cov workflow.

# Are these changes tested?

Yes.

---------

Co-authored-by: Jay White <[email protected]>

.github/workflows/lint-and-test.yml

@@ -136,6 +136,41 @@ jobs:
       - name: Run clippy::pedantic for proof-of-sql-parser
         run: cargo clippy --lib -p proof-of-sql-parser -- -D clippy::pedantic
 
+  coverage:
+    name: Code Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v3
+      - name: Install Dependencies
+        run: sudo apt-get update && sudo apt-get install -y clang lld
+      - uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Clean Previous Coverage Artifacts
+        run: cargo llvm-cov clean --workspace
+      - name: Run Tests to Generate Coverage Data (All Features)
+        run: cargo llvm-cov --no-report --all-features
+      #- name: Run Tests to Generate Coverage Data (Rayon Only)
+      #  run: cargo llvm-cov --no-report --no-default-features --features="rayon"
+      #- name: Run Tests to Generate Coverage Data (Blitzar Only)
+      #  run: cargo llvm-cov --no-report --no-default-features --features="blitzar"
+      #- name: Run Tests to Generate Coverage Data (std only)
+      #  run: cargo llvm-cov --no-report --no-default-features --features="std"
+      - name: Generate Final LCOV Report (Merged Coverage)
+        run: cargo llvm-cov report --summary-only --fail-under-lines 90
+      # Future CodeCov Integration
+      # To integrate with CodeCov in the future,, follow these steps: 
+      # 1. Add the CodeCov token to the repository secrets.
+      # 2. Use the CodeCov Action to upload the coverage report. For more detailed info refer to [CodeCov Documentation](https://docs.codecov.com/docs).
+      #
+      # - name: Generate Final LCOV Report (Merged Coverage)
+      #   run: cargo llvm-cov report --lcov --output-path lcov.info --fail-under-lines 95
+      # - name: Upload Coverage to Codecov
+      # uses: codecov/codecov-action@v2
+      # with:
+      #   token: ${{ secrets.CODECOV_TOKEN }}
+      #   files: lcov.info
+      #   fail_ci_if_error: true
+
   # Run cargo fmt --all -- --config imports_granularity=Crate,group_imports=One --check
   format:
     name: Format

CONTRIBUTING.md

@@ -14,6 +14,7 @@ The following guideline is heavily based on the [Angular Project Guideline](http
    - [Submitting a Pull Request (PR)](#submit-pr)
    - [Addressing review feedback](#address-review)
    - [Updating the commit message](#updating-commit-message)
+   - [Running Code Coverage Locally](#coverage-locally)
    - [After your pull request is merged](#after-pr-merged)
  - [Coding Rules](#rules)
  - [Commit Message Guidelines](#commit-guidelines)
@@ -246,6 +247,12 @@ In order to update the commit message of the last commit on your branch:
 
 NOTE: If you need to update the commit message of an earlier commit, you can use `git rebase` in interactive mode. See the [git docs](https://git-scm.com/docs/git-rebase#_interactive_mode) for more details.
 
+### <a name="coverage-locally"></a> Running Code Coverage Locally 
+To run code coverage locally, install `cargo-llvm-cov` by following the instructions here: [cargo-llvm-cov Installation](https://github.com/taiki-e/cargo-llvm-cov).
+
+For users of VSCode, you can display coverage reports directly in the IDE by following these instructions: [Display Coverage in VSCode](https://github.com/taiki-e/cargo-llvm-cov?tab=readme-ov-file#display-coverage-in-vs-code).
+
+You can exclude specific functions from coverage by adding an attribute to your code: [Exclude Functions from Coverage](https://github.com/taiki-e/cargo-llvm-cov?tab=readme-ov-file#exclude-function-from-coverage).
 
 ### <a name="after-pr-merged"></a> After your pull request is merged
 
@@ -275,7 +282,6 @@ After your pull request is merged, you can safely delete your branch and pull th
     git pull --ff upstream main
     ```
 
-
 ## <a name="rules"></a> Coding Rules
 To ensure consistency throughout the source code, keep these rules in mind as you are working: