Support parsing of existing files

psi-java/src/main/kotlin/io/spine/tools/psi/java/Parser.kt

@@ -30,7 +30,10 @@ import com.intellij.ide.highlighter.JavaFileType
 import com.intellij.openapi.project.Project
 import com.intellij.psi.PsiFileFactory
 import com.intellij.psi.PsiJavaFile
+import java.io.File
 import java.time.Instant
+import com.intellij.openapi.vfs.local.CoreLocalFileSystem
+import com.intellij.psi.PsiManager
 import java.util.*
 
 /**
@@ -42,6 +45,14 @@ public class Parser(private val project: Project) {
         PsiFileFactory.getInstance(project)
     }
 
+    private val localFileSystem by lazy {
+        CoreLocalFileSystem()
+    }
+
+    private val psiManager by lazy {
+        PsiManager.getInstance(project)
+    }
+
     /**
      * Creates a new instance of [PsiJavaFile] with the given code and auto-generated name.
      *
@@ -50,14 +61,34 @@ public class Parser(private val project: Project) {
     public fun parse(javaSource: String): PsiJavaFile =
         syntheticFile(javaSource)
 
+    /**
+     * Parses the given file and returns the corresponding [PsiJavaFile].
+     */
+    public fun parse(file: File): PsiJavaFile {
+        require(file.toString().endsWith(FILE_SUFFIX)) {
+            "The file `$file` must have the `$FILE_SUFFIX` extension."
+        }
+        require(file.exists()) {
+            "The file `$file` does not exist."
+        }
+        val found = localFileSystem.findFileByIoFile(file)
+        require(found != null) {
+            "Unable to locate the file `$file` in the local file system."
+        }
+        psiManager.findFile(found)?.let {
+            return it as PsiJavaFile
+        }
+        error("Unable to parse the file `$file`.")
+    }
+
     /**
      * Creates a new instance of `PsiJavaFile` with the given content, auto-generated name, and
      * the current time as the modification timestamp.
      *
      * The instance also has the event system enabled to allow obtaining `VirtualFile` instance.
      */
     private fun syntheticFile(javaSource: String): PsiJavaFile {
-        val fileName = "__to_parse_${UUID.randomUUID()}__.java"
+        val fileName = "__to_parse_${UUID.randomUUID()}__$FILE_SUFFIX"
         val modificationStamp = Instant.now().toEpochMilli()
         val file = fileFactory.createFileFromText(
             fileName,
@@ -68,4 +99,8 @@ public class Parser(private val project: Project) {
         )
         return file as PsiJavaFile
     }
+
+    private companion object {
+        const val FILE_SUFFIX = ".java"
+    }
 }

psi-java/src/test/kotlin/io/spine/tools/psi/java/FileParsingSpec.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2023, TeamDev. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Redistribution and use in source and/or binary forms, with or without
+ * modification, must retain the above copyright notice and the following
+ * disclaimer.
+ *
+ * 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
+ * OWNER 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.
+ */
+
+package io.spine.tools.psi.java
+
+import java.io.File
+import io.kotest.matchers.shouldNotBe
+import org.junit.jupiter.api.BeforeAll
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import org.junit.jupiter.api.io.TempDir
+
+@DisplayName("Parsing of existing Java file should")
+class FileParsingSpec: ParsingTest() {
+
+    companion object {
+
+        lateinit var file: File
+        private const val fileName = "FileOnDisk.java"
+
+        @BeforeAll
+        @JvmStatic
+        fun createFile(@TempDir tempDir: File) {
+            file = tempDir.resolve(fileName)
+            val code = readResource(fileName)
+            file.writeText(code)
+        }
+    }
+
+    @Test
+    fun `parse existing file`() {
+        val psiFile = parser.parse(file)
+        psiFile shouldNotBe null
+    }
+
+    @Test
+    fun `require file to have proper extension`() {
+        assertThrows<IllegalArgumentException> {
+            parser.parse(File("file.txt"))
+        }
+    }
+
+    @Test
+    fun `not parse non-existing file`() {
+        val nonExistingFile = File("non-existing-file.java")
+        assertThrows<IllegalArgumentException> {
+            parser.parse(nonExistingFile)
+        }
+    }
+}

psi-java/src/test/resources/FileOnDisk.java

@@ -0,0 +1,8 @@
+/**
+ * This is a stub Java source file to test pasing existing Java files.
+ */
+class FileOnDisk {
+    public static void main(String[] args) {
+        System.out.println("Hello, World!");
+    }
+}