Fix configuration cache misses caused by JGit shelling out to git (#1837

 fixes #1806)

CHANGES.md

@@ -18,6 +18,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * Support configuration of mirrors for P2 repositories in maven DSL ([#1697](https://github.com/diffplug/spotless/issues/1697)).
 ### Fixed
 * Fix support for plugins when using Prettier version `3.0.0` and newer. ([#1802](https://github.com/diffplug/spotless/pull/1802))
+* Fix configuration cache issue around `external process started '/usr/bin/git --version'`. ([#1806](https://github.com/diffplug/spotless/issues/1806))
 ### Changes
 * Bump default `flexmark` version to latest `0.64.0` -> `0.64.8`. ([#1801](https://github.com/diffplug/spotless/pull/1801))
 * Bump default `ktlint` version to latest `0.50.0` -> `1.0.0`. ([#1808](https://github.com/diffplug/spotless/pull/1808))

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/GitRatchetGradle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2021 DiffPlug
+ * Copyright 2020-2023 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,10 +19,33 @@
 
 import javax.annotation.Nullable;
 
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.eclipse.jgit.util.FS;
+import org.eclipse.jgit.util.SystemReader;
+
 import com.diffplug.spotless.extra.GitRatchet;
 
 /** Gradle implementation of GitRatchet. */
 public class GitRatchetGradle extends GitRatchet<File> {
+	static {
+		preventJGitFromCallingExecutables();
+	}
+
+	static void preventJGitFromCallingExecutables() {
+		SystemReader reader = SystemReader.getInstance();
+		SystemReader.setInstance(new DelegatingSystemReader(reader) {
+			@Override
+			public String getenv(String variable) {
+				if ("PATH".equals(variable)) {
+					return "";
+				} else {
+					return super.getenv(variable);
+				}
+			}
+		});
+	}
+
 	@Override
 	protected File getDir(File project) {
 		return project;
@@ -32,4 +55,52 @@ protected File getDir(File project) {
 	protected @Nullable File getParent(File project) {
 		return project.getParentFile();
 	}
+
+	static class DelegatingSystemReader extends SystemReader {
+		final SystemReader reader;
+
+		DelegatingSystemReader(SystemReader reader) {
+			this.reader = reader;
+		}
+
+		@Override
+		public String getHostname() {
+			return reader.getHostname();
+		}
+
+		@Override
+		public String getenv(String variable) {
+			return reader.getProperty(variable);
+		}
+
+		@Override
+		public String getProperty(String key) {
+			return reader.getProperty(key);
+		}
+
+		@Override
+		public FileBasedConfig openUserConfig(Config parent, FS fs) {
+			return reader.openUserConfig(parent, fs);
+		}
+
+		@Override
+		public FileBasedConfig openSystemConfig(Config parent, FS fs) {
+			return reader.openSystemConfig(parent, fs);
+		}
+
+		@Override
+		public FileBasedConfig openJGitConfig(Config parent, FS fs) {
+			return reader.openJGitConfig(parent, fs);
+		}
+
+		@Override
+		public long getCurrentTime() {
+			return reader.getCurrentTime();
+		}
+
+		@Override
+		public int getTimezone(long when) {
+			return reader.getTimezone(when);
+		}
+	}
 }