CI run-tests script now attempts to detect Apple Clang 15 and other unsupported regression-tests compiler versions (#972)

* CI run-tests script now prints the compiler version if we don't support it

The `macos-13` runner has both Apple Clang 14 and 15 installed, and some CI workflow runs appear to use 15, causing spurious failures.

* If the CI run-tests script finds Apple Clang 15 try and switch to 14

Author: bluetarpmedia

regression-tests/run-tests.sh

@@ -130,31 +130,39 @@ if [[ "$cxx_compiler" == *"cl.exe"* ]]; then
     compiler_version=$(cl.exe)
 else
     compiler_cmd="$cxx_compiler -I../../../include -std=c++20 -pthread -o "
-    
-    compiler_ver=$("$cxx_compiler" --version)
-    if [[ "$compiler_ver" == *"Apple clang version 14.0"* ]]; then
+    compiler_version=$("$cxx_compiler" --version)
+
+    # We don't currently support Apple Clang 15 so try and switch to 14
+    if [[ "$compiler_version" == *"Apple clang version 15.0"* ]]; then
+        printf "Found Apple Clang 15, attempting to switch to Apple Clang 14"
+        cxx_compiler=$(xcodebuild -find clang++)
+        compiler_version=$("$cxx_compiler" --version)
+    fi
+
+    if [[ "$compiler_version" == *"Apple clang version 14.0"* ]]; then
         exec_out_dir="$expected_results_dir/apple-clang-14"
-    elif [[ "$compiler_ver" == *"clang version 12.0"* ]]; then 
+    elif [[ "$compiler_version" == *"clang version 12.0"* ]]; then 
         exec_out_dir="$expected_results_dir/clang-12"
-    elif [[ "$compiler_ver" == *"clang version 15.0"* ]]; then 
+    elif [[ "$compiler_version" == *"clang version 15.0"* ]]; then 
         exec_out_dir="$expected_results_dir/clang-15"
-    elif [[ "$compiler_ver" == *"g++-10"* ]]; then
+    elif [[ "$compiler_version" == *"g++-10"* ]]; then
         exec_out_dir="$expected_results_dir/gcc-10"
-    elif [[ "$compiler_ver" == *"g++-12"* ||
-            "$compiler_ver" == *"g++-13"*
+    elif [[ "$compiler_version" == *"g++-12"* ||
+            "$compiler_version" == *"g++-13"*
          ]]; then
         exec_out_dir="$expected_results_dir/gcc-13"
+    else
+        printf "Unhandled compiler version:\n$compiler_version\n\n"
     fi
-
-    compiler_version=$("$cxx_compiler" --version)
 fi
 
 if [[ -d "$exec_out_dir" ]]; then
     printf "Full compiler version for '$cxx_compiler':\n$compiler_version\n\n"
 
     printf "Directory with reference compilation/execution files to use:\n$exec_out_dir\n\n"
 else
-    printf "not found for compiler: '$cxx_compiler'\n\n"
+    printf "Directory with reference compilation/execution files not found for compiler: '$cxx_compiler'\n\n"
+    exit 2
 fi
 
 ################