Add test for a JavacTool-based compiler that doesn't use standard JavaFileObjects

java/ql/integration-tests/java/javac-tool-custom-file/Compiler.java

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+import javax.lang.model.element.Modifier;
+import javax.lang.model.element.NestingKind;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.ToolProvider;
+import java.io.*;
+import java.net.URI;
+import java.util.List;
+import java.util.Objects;
+
+public class Compiler {
+    public static void main(String[] args) {
+
+        JavaCompiler.CompilationTask jc = ToolProvider.getSystemJavaCompiler().getTask(
+                null, null, null, null, null,
+                List.of(
+                        new JavaFileObject() {
+                            @Override
+                            public Kind getKind() {
+                                return Kind.SOURCE;
+                            }
+
+                            @Override
+                            public boolean isNameCompatible(String simpleName, Kind kind) {
+                                return Objects.equals(simpleName, "Main");
+                            }
+
+                            @Override
+                            public NestingKind getNestingKind() {
+                                return null;
+                            }
+
+                            @Override
+                            public Modifier getAccessLevel() {
+                                return null;
+                            }
+
+                            @Override
+                            public URI toUri() {
+                                return URI.create("https://nonesuch.imaginary/somedir/Main.java");
+                            }
+
+                            @Override
+                            public String getName() {
+                                return "Main.java";
+                            }
+
+                            @Override
+                            public InputStream openInputStream() throws IOException {
+                                return new ByteArrayInputStream(this.getCharContent(true).toString().getBytes());
+                            }
+
+                            @Override
+                            public OutputStream openOutputStream() throws IOException {
+                                throw new IOException("No output allowed");
+                            }
+
+                            @Override
+                            public Reader openReader(boolean ignoreEncodingErrors) throws IOException {
+                                return new StringReader(this.getCharContent(ignoreEncodingErrors).toString());
+                            }
+
+                            @Override
+                            public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
+                                return "public class Main { }";
+                            }
+
+                            @Override
+                            public Writer openWriter() throws IOException {
+                                throw new IOException("No output allowed");
+                            }
+
+                            @Override
+                            public long getLastModified() {
+                                return 0;
+                            }
+
+                            @Override
+                            public boolean delete() {
+                                return false;
+                            }
+
+                            @Override
+                            public String toString() {
+                                return "In-memory file with URI " + this.toUri();
+                            }
+                        }
+                )
+        );
+
+        jc.call();
+    }
+}

java/ql/integration-tests/java/javac-tool-custom-file/test.expected

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+| Main |

java/ql/integration-tests/java/javac-tool-custom-file/test.py

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+import commands
+
+def test(codeql, java):
+    commands.run("javac Compiler.java")
+    codeql.database.create(command = "java Compiler")

java/ql/integration-tests/java/javac-tool-custom-file/test.ql

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+import java
+
+from Class c
+where c.fromSource()
+select c.getName()