Check in CI that BUILD.bazel is up to date

The "Check amalgamation" workflow now also regenerates BUILD.bazel, so a
pull request that adds, renames, or removes a header without updating
the Bazel header list fails, and the attached amalgamation.patch
contains the fix. The failure comment and the contribution guidelines
mention the new check, and the comment now links to the existing
"Amalgamate the source code" section instead of the "Files to change"
anchor that was removed in #4560.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/CONTRIBUTING.md

@@ -158,6 +158,15 @@ make amalgamate
 Running `make amalgamate` will also apply automatic formatting to the source files using
 [`Artistic Style`](https://astyle.sourceforge.net/). This formatting may modify your source files in-place. Be certain to review and commit any changes to avoid unintended formatting diffs in commits.
 
+If you add, rename, or remove a header in `include/nlohmann`, also regenerate the header list in
+[`BUILD.bazel`](https://github.com/nlohmann/json/blob/develop/BUILD.bazel) (requires CMake) by executing:
+
+```shell
+make BUILD.bazel
+```
+
+The amalgamation check in CI fails if any of these generated files is out of date.
+
 ## Recommended documentation
 
 - The library’s [README file](https://github.com/nlohmann/json/blob/master/README.md) is an excellent starting point to

.github/workflows/check_amalgamation.yml

@@ -57,13 +57,16 @@ jobs:
           python3 -mvenv venv
           venv/bin/pip3 install -r $MAIN_DIR/tools/astyle/requirements.txt
 
-      - name: Regenerate amalgamation and formatting
+      - name: Regenerate amalgamation, formatting, and BUILD.bazel
         run: |
           cd $MAIN_DIR
 
           python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json.json -s .
           python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json_fwd.json -s .
 
+          # the header list of the Bazel "json" target must match the files in include/
+          cmake -P cmake/scripts/gen_bazel_build_file.cmake
+
           ${{ github.workspace }}/venv/bin/astyle --project=tools/astyle/.astylerc --suffix=none --quiet \
             $INCLUDE_DIR/json.hpp $INCLUDE_DIR/json_fwd.hpp
 
@@ -87,7 +90,7 @@ jobs:
           mkdir -p ${{ github.workspace }}/patch
           git diff --patch --no-color > ${{ github.workspace }}/patch/amalgamation.patch
           if [ -s ${{ github.workspace }}/patch/amalgamation.patch ]; then
-            echo "The source code has not been amalgamated/formatted correctly. Diff:"
+            echo "The source code has not been amalgamated/formatted correctly or BUILD.bazel is out of date. Diff:"
             cat ${{ github.workspace }}/patch/amalgamation.patch
             echo "has_diff=true" >> "$GITHUB_OUTPUT"
           else

.github/workflows/comment_check_amalgamation.yml

@@ -95,13 +95,13 @@ jobs:
               issue_number: issue_number,
               owner: context.repo.owner,
               repo: context.repo.repo,
-              body: '## 🔴 Amalgamation check failed! 🔴\nThe source code has not been amalgamated and/or formatted correctly.'
+              body: '## 🔴 Amalgamation check failed! 🔴\nThe source code has not been amalgamated and/or formatted correctly, or `BUILD.bazel` is out of date.'
                     + (hasPatch ? '\n\n📎 A ready-to-apply patch is attached to the [failed workflow run](' + runUrl + ') as the `amalgamation-patch` artifact.'
                                   + ' Download it, then apply it locally from the repository root with:'
                                   + '\n\n```shell\ngit apply amalgamation.patch\n```\n\n'
                                   + 'This does not require installing astyle yourself.'
                                 : '')
                     + (first ? '\n\n@' + author + ' Please read and follow the [Contribution Guidelines]'
-                               + '(https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#files-to-change).'
+                               + '(https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#amalgamate-the-source-code).'
                              : '')
               })