use try catch clause for more accurate relative path check.

Author: neetopia

common-util/src/main/kotlin/com/google/devtools/ksp/processing/impl/CodeGeneratorImpl.kt

@@ -156,11 +156,13 @@ class CodeGeneratorImpl(
     }
 
     private val File.relativeFile: File
-        get() =
-            if (this.startsWith(buildDir))
+        get() {
+            val buildDirPrefix = if (buildDir.path.startsWith("/")) buildDir.path else buildDir.path.replace("\\", "/")
+            return if (this.startsWith(buildDirPrefix))
                 relativeTo(buildDir)
             else
                 relativeTo(projectBase)
+        }
 
     private fun associate(sources: List<KSFile>, outputPath: File) {
         if (!isIncremental)

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt

@@ -230,11 +230,14 @@ class IncrementalContext(
 
     // Ugly, but better than copying the private logics out of stdlib.
     // TODO: get rid of `relativeTo` if possible.
-    private fun String.toRelativeFile(): File =
-        if (this.startsWith(buildDir.path))
+    private fun String.toRelativeFile(): File {
+        val buildDirPrefix = if (buildDir.path.startsWith("/")) buildDir.path else buildDir.path.replace("\\", "/")
+        return if (this.startsWith(buildDirPrefix)) {
             File(this).relativeTo(buildDir)
-        else
+        } else {
             File(this).relativeTo(baseDir)
+        }
+    }
 
     private val KSFile.relativeFile
         get() = filePath.toRelativeFile()

integration-tests/src/test/kotlin/com/google/devtools/ksp/test/PlaygroundIT.kt

@@ -65,6 +65,28 @@ class PlaygroundIT {
         project.restore("workload/build.gradle.kts")
     }
 
+    @Test
+    fun testArbitraryBuildDir() {
+        Assume.assumeTrue(System.getProperty("os.name").startsWith("Windows", ignoreCase = true))
+        val gradleRunner = GradleRunner.create().withProjectDir(project.root)
+
+        File(project.root, "workload/build.gradle.kts")
+            .appendText("project.buildDir = File(\"D:/build/\")")
+        val result = gradleRunner.withArguments("build").build()
+
+        Assert.assertEquals(TaskOutcome.SUCCESS, result.task(":workload:build")?.outcome)
+
+        val artifact = File("D:/build/libs/workload-1.0-SNAPSHOT.jar")
+        Assert.assertTrue(artifact.exists())
+
+        JarFile(artifact).use { jarFile ->
+            Assert.assertTrue(jarFile.getEntry("TestProcessor.log").size > 0)
+            Assert.assertTrue(jarFile.getEntry("hello/HELLO.class").size > 0)
+            Assert.assertTrue(jarFile.getEntry("g/G.class").size > 0)
+            Assert.assertTrue(jarFile.getEntry("com/example/AClassBuilder.class").size > 0)
+        }
+    }
+
     @Test
     fun testAllowSourcesFromOtherPlugins() {
         fun checkGBuilder() {