Fix some local version issues using black and also "make format-pr" (#3783)

* build: make format-pr more robust

- Support both 'main' and 'master' as base branch
- Only pass existing files to the formatter
- Eliminates noisy "ERROR: X jobs failed" when files were deleted
- handles filenames with spaces

* ci: run formatting check on ubuntu-24.04 (Python 3.12 instead of3.10)

* update coding-conventions (prints black version)

Author: nrnhines

.github/workflows/formatting.yml

@@ -18,7 +18,7 @@ on:
 jobs:
   all:
     name: C/C++, CMake and Python
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     timeout-minutes: 5
     steps:
       - uses: actions/checkout@v4

CMakeLists.txt

@@ -949,21 +949,43 @@ add_custom_target(
   COMMAND ${PROJECT_SOURCE_DIR}/external/coding-conventions/bin/format
   WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})
 
-# Prepare a shell script to format only files modified with respect to master branch
+# Prepare a shell script to format only files modified with respect to master/main branch that still
+# exist on disk (filters out deleted files).
 file(
   WRITE ${CMAKE_CURRENT_BINARY_DIR}/format-pr.sh
-  "\
-#!bash\n\
-set -e\n\
-cmd='cd ${PROJECT_SOURCE_DIR} && external/coding-conventions/bin/format `git diff --name-only master`'\n\
-echo $cmd\n\
-cd ${PROJECT_SOURCE_DIR} && external/coding-conventions/bin/format `git diff --name-only master`\n\
+  "#!/bin/bash
+set -euo pipefail
+
+# Try 'main' first, then fall back to 'master'
+for base in main master; do
+    if git rev-parse --verify \"\$base\" >/dev/null 2>&1; then
+        BASE_BRANCH=\"\$base\"
+        break
+    fi
+done
+
+if [ -z \"\${BASE_BRANCH:-}\" ]; then
+    echo \"Error: Neither 'main' nor 'master' branch found.\" >&2
+    exit 1
+fi
+
+echo \"Formatting changes vs '\$BASE_BRANCH' (existing files only)...\" >&2
+
+# Get changed files (null-delimited so names with spaces work), only pass
+# files that still exist.
+git diff -z --name-only \"\$BASE_BRANCH\" | \\
+while IFS= read -r -d '' file; do
+    if [ -e \"\$file\" ]; then
+        printf '%s\\0' \"\$file\"
+    fi
+done | \\
+xargs -0 --no-run-if-empty external/coding-conventions/bin/format \"\$@\"
 ")
 
 add_custom_target(
   format-pr
   COMMAND bash ${CMAKE_CURRENT_BINARY_DIR}/format-pr.sh
-  COMMENT "Format only files modified with respect to master branch."
+  COMMENT "Format only files modified with respect to main/master (existing files only)"
   WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})
 
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