build.gradle: only use clang-format when specified

build.gradle

@@ -26,15 +26,31 @@ spotless {
     // formatAnnotations()
 
     // Use a different clang-format binary with -PclangFormat=clang-format-15.
-    def clangFormatBinary = (String) project.findProperty('clangFormat') ?: 'clang-format'
-    def clangOutput = new ByteArrayOutputStream()
-    exec {
-      commandLine clangFormatBinary, '--version'
-      standardOutput = clangOutput
+    // FIXME: make clang-format default in the future
+    // def clangFormatBinary = (String) project.findProperty('clangFormat') ?: 'clang-format'
+    def clangFormatBinary = (String) project.findProperty('clangFormat')
+    if (clangFormatBinary) {
+      def clangVersion = (String) project.findProperty('clangVersion')
+      if (!clangVersion) {
+        try {
+          // Try to read clang-format version if not specified
+          def clangOutput = new ByteArrayOutputStream()
+          exec {
+            ignoreExitValue = true
+            commandLine clangFormatBinary, '--version'
+            standardOutput = clangOutput
+          }
+          clangVersion = (String) (clangOutput.toString() =~ /\d+\.\d+\.\d+/)[0]
+        } catch (IndexOutOfBoundsException ignored) {
+          logger.warn("Failed to read clang-format version using '{}': no version information found", clangFormatBinary)
+        } catch (Exception e) {
+          logger.warn("Failed to read clang-format version using '{}': {}", clangFormatBinary, e.getMessage())
+        }
+      }
+      if (clangVersion) {
+        clangFormat(clangVersion).pathToExe(clangFormatBinary).style('file')
+      }
     }
-    def clangVersion = (String) (clangOutput.toString() =~ /\d+\.\d+\.\d+/)[0]
-    // FIXME: enable clangFormat in the future.
-//    clangFormat(clangVersion).pathToExe(clangFormatBinary).style('file')
   }
 }