Coding style: Require clang-format 13

We currently use clang-format 10 which has shown to produce unexpected
output. This is annoying for PR submitters as the CI forces non-optimal
code layout, especially when submitters use a later clang-format version
which does not show this behavior.

This commit changes CI to use clang-format 13 and updates relevant
clang-format inline docs.

Related: jamulussoftware#2552

.clang-format

@@ -1,12 +1,12 @@
 ---
-# Style for Clang-Format version 10
-# https://releases.llvm.org/10.0.0/tools/clang/docs/ClangFormatStyleOptions.html
+# Style for clang-format version 13
+# https://releases.llvm.org/13.0.0/tools/clang/docs/ClangFormatStyleOptions.html
 BasedOnStyle: LLVM
 AccessModifierOffset: -4
 AlignConsecutiveAssignments: true
 AlignConsecutiveDeclarations: true
 AlignConsecutiveMacros: true
-# Alignment of Consecutive Assignments/Declarations/Macros can be changed to `AcrossEmptyLinesAndComments` with Clang-Format version 12
+# Alignment of Consecutive Assignments/Declarations/Macros can be changed to `AcrossEmptyLinesAndComments` now that we require clang-format >=12
 #AlignConsecutiveAssignments: AcrossEmptyLinesAndComments
 #AlignConsecutiveDeclarations: AcrossEmptyLinesAndComments
 #AlignConsecutiveMacros: AcrossEmptyLinesAndComments

.github/workflows/coding-style-check.yml

@@ -9,15 +9,15 @@ on:
 
 jobs:
   clang-format:
-    name: Verify Clang-Format compliance
+    name: Verify clang-format (v13) compliance
     permissions:
       contents: read
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
     - uses: DoozyX/clang-format-lint-action@2a28e3a8d9553f244243f7e1ff94f6685dff87be
       with:
-        clangFormatVersion: 10
+        clangFormatVersion: 13
         # When updating the extension list, remember to update
         # Jamulus.pro's CLANG_SOURCES as well.
         extensions: 'cpp,h,mm'

CONTRIBUTING.md

@@ -24,6 +24,9 @@ If a feature or function can be achieved in another way by another system or met
 
 You can use your editor's or IDE's clang-format support to accomplish that.
 On the command line, you can run `make clang_format` to do the same before committing.
+Please use the same clang-format version which we use.
+Other versions might produce slightly different output.
+You can find the currently used version in the [workflow definition](https://github.com/jamulussoftware/jamulus/blob/master/.github/workflows/coding-style-check.yml#L20].
 
 Do not use diff/patch to send your code changes but create a Github fork of the Jamulus code and create a Pull Request when you are done.