Split Windows path escape code to dedicated method

And explain why it needs to be so many backslashes. XD

src/test/java/sc/fiji/labkit/ui/plugin/CalculateProbabilityMapWithLabkitIJ1PluginTest.java

@@ -61,7 +61,7 @@ public void test() throws IOException {
 				.replace('\'', '"')
 				.replace("INPUT_TIF", inputImage)
 				.replace("SEGMENTER_FILE", blobsModel)
-				.replace("OUTPUT_TIF", outputImage.getAbsolutePath().replaceAll("\\\\", "\\\\\\\\"));
+				.replace("OUTPUT_TIF", MacroUtils.safePath(outputImage));
 			new Interpreter().run(macro);
 			assertTrue(outputImage.exists());
 			assertTrue(outputImage.length() > 0);

src/test/java/sc/fiji/labkit/ui/plugin/MacroUtils.java

@@ -0,0 +1,61 @@
+/*-
+ * #%L
+ * The Labkit image segmentation tool for Fiji.
+ * %%
+ * Copyright (C) 2017 - 2024 Matthias Arzt
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+package sc.fiji.labkit.ui.plugin;
+
+import java.io.File;
+
+public final class MacroUtils {
+
+	private MacroUtils() { }
+
+	/**
+	 * Escapes backslashes in file paths (which is crucial on Windows)
+	 * so they work as desired when embedded into an ImageJ macro.
+	 */
+	public static String safePath(File file) {
+		// This regex replacement is tricky:
+		//
+		// 1. We must escape the Java strings, because the expression
+		//    "\\" represents the literal backslash character '\'.
+		//
+		// 2. Then we must use a second level of escaping for the regex,
+		//    because we need to pass `\\` as the pattern to match or else
+		//    the regex logic won't understand we're talking about a
+		//    literal backslash rather than an escaped something-or-other.
+		//
+		// Together, this expression replaces single literal backslashes
+		// with double literal backslashes.
+		//
+		// We then we end up with an ImageJ macro that has a `\\` for
+		// each backslash within the embedded paths, and ImageJ's
+		// macro execution logic unescapes them accordingly.
+
+		return file.getAbsolutePath().replaceAll("\\\\", "\\\\\\\\");
+	}
+}

src/test/java/sc/fiji/labkit/ui/plugin/SegmentImageWithLabkitIJ1PluginTest.java

@@ -61,7 +61,7 @@ public void test() throws IOException {
 				.replace('\'', '"')
 				.replace("INPUT_TIF", inputImage)
 				.replace("SEGMENTER_FILE", blobsModel)
-				.replace("OUTPUT_TIF", outputImage.getAbsolutePath().replaceAll("\\\\", "\\\\\\\\"));
+				.replace("OUTPUT_TIF", MacroUtils.safePath(outputImage));
 			new Interpreter().run(macro);
 			assertTrue(outputImage.exists());
 			ImagePlus expected = IJ.openImage(source);