feat: implement test helper for custom workspaces built on demand

Author: S-furi

completions/src/test/kotlin/lsp/utils/WorkspaceUtils.kt

@@ -0,0 +1,56 @@
+package lsp.utils
+
+import java.nio.file.Files
+import kotlin.io.path.ExperimentalPathApi
+import kotlin.io.path.absolutePathString
+import kotlin.io.path.copyToRecursively
+import kotlin.io.path.deleteRecursively
+import kotlin.io.path.toPath
+
+object WorkspaceUtils {
+    private const val TEMPLATE_NAME = "root-template"
+    private val workspacePath = this::class.java.getResource("/lsp/workspaces")?.toURI()?.toPath()
+        ?: error("no workspaces folder found")
+
+    private const val GENERATED_NAME_PREFIX = "lsp-workspace-root-"
+
+    @OptIn(ExperimentalPathApi::class)
+    fun withTempWorkspace(
+        kotlinVersion: String,
+        block: suspend (localWorkspacePath: String, remoteWorkspacePath: String) -> Unit
+    ) {
+        val template = workspacePath.resolve(TEMPLATE_NAME)
+        require(Files.exists(template)) { "no template found" }
+
+        val dstWorkspaceName = "$GENERATED_NAME_PREFIX$kotlinVersion"
+        val (dstDir, alreadyExists) = workspacePath.resolve(dstWorkspaceName).let {
+            it to it.toFile().mkdirs()
+        }
+
+        if (!alreadyExists) {
+            template.copyToRecursively(target = dstDir, overwrite = false, followLinks = false)
+
+            val buildFile = dstDir.resolve("build.gradle.kts").also {
+                require(Files.exists(it)) { "no build file found in dst dir" }
+            }.toFile()
+
+            val kotlinVersionPlaceholder = "{{kotlin_version}}"
+            val pluginsPlaceholder = "{{plugins}}"
+            val dependenciesPlaceholder = "{{dependencies}}"
+
+            val newContent: String = listOf(kotlinVersionPlaceholder, pluginsPlaceholder, dependenciesPlaceholder)
+                .zip(listOf(setOf(kotlinVersion), emptySet(), emptySet()))
+                .fold(buildFile.readText()) { acc, (placeholder, values) ->
+                    acc.replace(placeholder, values.joinToString("\n    "))
+                }
+            buildFile.writeText(newContent)
+        }
+
+        val localPath = dstDir.absolutePathString()
+        val remotePath = "/workspaces/$dstWorkspaceName"
+
+        block(localPath, remotePath)
+
+        dstDir.deleteRecursively()
+    }
+}