Fix #755

src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java

@@ -272,7 +272,7 @@ public final class CompileConfiguration {
 	private static Path getLockFile(Project project) {
 		final LoomGradleExtension extension = LoomGradleExtension.get(project);
 		final Path cacheDirectory = extension.getFiles().getUserCache().toPath();
-		final String pathHash = Checksum.toHex(project.getProjectDir().getAbsolutePath().getBytes(StandardCharsets.UTF_8)).substring(0, 16);
+		final String pathHash = Checksum.projectHash(project);
 		return cacheDirectory.resolve("." + pathHash + ".lock");
 	}
 

src/main/java/net/fabricmc/loom/util/Checksum.java

@@ -27,12 +27,14 @@ package net.fabricmc.loom.util;
 import java.io.File;
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 
 import com.google.common.hash.HashCode;
 import com.google.common.hash.Hashing;
 import com.google.common.io.BaseEncoding;
 import com.google.common.io.Files;
+import org.gradle.api.Project;
 import org.gradle.api.logging.Logger;
 import org.gradle.api.logging.Logging;
 
@@ -81,4 +83,9 @@ public class Checksum {
 	public static String toHex(byte[] bytes) {
 		return BaseEncoding.base16().lowerCase().encode(bytes);
 	}
+
+	public static String projectHash(Project project) {
+		String str = project.getProjectDir().getAbsolutePath() + ":" + project.getPath();
+		return toHex(str.getBytes(StandardCharsets.UTF_8)).substring(0, 16);
+	}
 }

src/test/groovy/net/fabricmc/loom/test/unit/ChecksumTest.groovy

@@ -0,0 +1,49 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2023 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.test.unit
+
+import net.fabricmc.loom.util.Checksum
+import org.gradle.api.Project
+import spock.lang.Specification
+
+class ChecksumTest extends Specification {
+	def "project hash"() {
+		given:
+			def project = Mock(Project)
+			project.getPath() >> path
+			project.getProjectDir() >> new File(dir)
+
+		when:
+			def hash = Checksum.projectHash(project)
+
+		then:
+			hash == expected
+
+		where:
+			path   | dir                                          | expected
+			":"    | "C://mod"                                    | "2f55736572732f6d"
+			":sub" | "/Users/test/Documents/modding/fabric-loom"  | "2f55736572732f74"
+	}
+}