[PATCH v2] ci: run `make sparse` as part of the GitHub workflow

From: Johannes Schindelin <johannes.schindelin@gmx.de>

Occasionally we receive reviews after patches were integrated, where `sparse` (https://sparse.docs.kernel.org/en/latest/ has more information on that project) identified problems such as file-local variables or functions being declared as global.

By running `sparse` as part of our Continuous Integration, we can catch such things much earlier. Even better: developers who activated GitHub Actions on their forks can catch such issues before even sending their patches to the Git mailing list.

This addresses https://github.com/gitgitgadget/git/issues/345

Note: Not even Ubuntu 20.04 ships with a new enough version of `sparse`
to accommodate Git's needs. The symptom looks like this:

    add-interactive.c:537:51: error: Using plain integer as NULL pointer

To counter that, we download and install the custom-built `sparse` package from the Azure Pipeline that we specifically created to address this issue.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    ci: run make sparse as a GitHub workflow
    
    One of the earliest open source static analyzers is called "sparse", and
    occasionally Ramsay Jones sends out mails on the Git mailing list that
    some function or other should be declared static because sparse found
    out that it is only used within the same file.
    
    Let's add a GitHub workflow running "make sparse".
    
    Example run:
    https://github.com/gitgitgadget/git/pull/994/checks?check_run_id=3065255116
    
    Changes since v1:
    
     * The job was folded into main.yml
     * The commit message and a code comment now explain why we have to
       download & install a custom sparse package instead of using Ubuntu's
       default one
     * The commit message now contains a link to the documentation of the
       sparse tool

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-994%2Fdscho%2Fci-enable-sparse-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-994/dscho/ci-enable-sparse-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/994

Range-diff vs v1:

 1:  d1af618dd73 ! 1:  8b631acfaa2 ci: run `make sparse` as a GitHub workflow
     @@ Metadata
      Author: Johannes Schindelin <Johannes.Schindelin@gmx.de>
      
       ## Commit message ##
     -    ci: run `make sparse` as a GitHub workflow
     +    ci: run `make sparse` as part of the GitHub workflow
      
          Occasionally we receive reviews after patches were integrated, where
     -    `sparse` identified problems such as file-local variables or functions
     -    being declared as global.
     +    `sparse` (https://sparse.docs.kernel.org/en/latest/ has more information
     +    on that project) identified problems such as file-local variables or
     +    functions being declared as global.
      
          By running `sparse` as part of our Continuous Integration, we can catch
          such things much earlier. Even better: developers who activated GitHub
     @@ Commit message
      
          This addresses https://github.com/gitgitgadget/git/issues/345
      
     +    Note: Not even Ubuntu 20.04 ships with a new enough version of `sparse`
     +    to accommodate Git's needs. The symptom looks like this:
     +
     +        add-interactive.c:537:51: error: Using plain integer as NULL pointer
     +
     +    To counter that, we download and install the custom-built `sparse`
     +    package from the Azure Pipeline that we specifically created to address
     +    this issue.
     +
          Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
      
     - ## .github/workflows/run-sparse.yml (new) ##
     -@@
     -+name: Run `sparse`
     -+
     -+on: [push, pull_request]
     -+
     -+jobs:
     + ## .github/workflows/main.yml ##
     +@@ .github/workflows/main.yml: jobs:
     +     - uses: actions/checkout@v1
     +     - run: ci/install-dependencies.sh
     +     - run: ci/run-static-analysis.sh
      +  sparse:
     ++    needs: ci-config
     ++    if: needs.ci-config.outputs.enabled == 'yes'
     ++    env:
     ++      jobname: sparse
      +    runs-on: ubuntu-20.04
      +    steps:
     -+    - name: Download the `sparse` package
     ++    - name: Download a current `sparse` package
     ++      # Ubuntu's `sparse` version is too old for us
      +      uses: git-for-windows/get-azure-pipelines-artifact@v0
      +      with:
      +        repository: git/git
      +        definitionId: 10
      +        artifact: sparse-20.04
     -+    - name: Install the `sparse` package
     ++    - name: Install the current `sparse` package
      +      run: sudo dpkg -i sparse-20.04/sparse_*.deb
     -+    - name: Install a couple of dependencies
     ++    - name: Install other dependencies
      +      run: |
      +        sudo apt-get install -q -y libssl-dev libcurl4-openssl-dev libexpat-dev gettext zlib1g-dev
      +    - uses: actions/checkout@v2
     -+    - name: make sparse
     -+      run: make sparse
     - \ No newline at end of file
     ++    - run: make sparse
     +   documentation:
     +     needs: ci-config
     +     if: needs.ci-config.outputs.enabled == 'yes'

 .github/workflows/main.yml | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)