Improve noargs message and add a help argument + detailed message

src/org/jetbrains/java/decompiler/main/decompiler/ConsoleDecompiler.java

@@ -16,11 +16,9 @@
 import java.nio.file.Paths;
 import java.util.*;
 import java.util.function.Function;
-import java.util.function.Supplier;
 import java.util.jar.JarOutputStream;
 import java.util.jar.Manifest;
 import java.util.stream.Stream;
-import java.util.zip.CheckedInputStream;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 import java.util.zip.ZipOutputStream;
@@ -60,6 +58,11 @@ else if (args.length > x+1) {
     }
     args = params.toArray(new String[params.size()]);
 
+    if (Arrays.stream(args).anyMatch(arg -> arg.equals("-h") || arg.equals("--help") || arg.equals("-help"))) {
+      ConsoleHelp.printHelp();
+      return;
+    }
+
     if (args.length < 2) {
       System.out.println(
         "Usage: java -jar fernflower.jar [-<option>=<value>]* [<source>]+ <destination>\n" +

src/org/jetbrains/java/decompiler/main/decompiler/ConsoleHelp.java

@@ -0,0 +1,114 @@
+package org.jetbrains.java.decompiler.main.decompiler;
+
+import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences;
+
+import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class ConsoleHelp {
+  private static final String[] DEFAULT_HELP = {
+    "Usage: java -jar quiltflower.jar [-<option>=<value>]* [<source>]+ <destination>",
+    "At least one source file or directory must be specified.",
+    "Options:",
+    "--help: Show this help",
+    "", "Saving options",
+    "A maximum of one of the options can be specified:",
+    "--file          - Write the decompiled source to a file",
+    "--folder        - Write the decompiled source to a folder",
+    "--legacy-saving - Use the legacy console-specific method of saving",
+    "If unspecified, the decompiled source will be automatically detected based on destination name.",
+    "", "General options",
+    "These options can be specified multiple times.",
+    "-e=<path>     - Add the specified path to the list of external libraries",
+    "-only=<class> - Only decompile the specified class",
+    "", "Additional options",
+    "These options take the last specified value.",
+    "They each are specified with a three-character name followed by an equals sign, followed by the value.",
+    "Booleans are traditionally indicated with `0` or `1`, but may also be specified with `true` or `false`.",
+    "Because of this, an option indicated as a boolean may actually be a number."
+    // Options are added at runtime
+  };
+
+  static void printHelp() {
+    for (String line : DEFAULT_HELP) {
+      System.out.println(line);
+    }
+
+    List<Field> fields = Arrays.stream(IFernflowerPreferences.class.getDeclaredFields())
+      .filter(field -> field.getType() == String.class)
+      .collect(Collectors.toList());
+
+    Map<String, Object> defaults = IFernflowerPreferences.DEFAULTS;
+
+    for (Field field : fields) {
+      IFernflowerPreferences.Name name = field.getAnnotation(IFernflowerPreferences.Name.class);
+      IFernflowerPreferences.Description description = field.getAnnotation(IFernflowerPreferences.Description.class);
+
+      String paramName;
+      try {
+        paramName = (String) field.get(null);
+      } catch (IllegalAccessException e) {
+        continue;
+      }
+
+      if (paramName.length() != 3) {
+        continue;
+      }
+
+      StringBuilder sb = new StringBuilder();
+      sb.append("-").append(paramName).append("=<");
+
+      String type;
+      String defaultValue = (String) defaults.get(paramName);
+      if (defaultValue == null) {
+        sb.append("string>");
+        type = null;
+      } else if (defaultValue.equals("0") || defaultValue.equals("1")) {
+        sb.append("bool>  ");
+        type = "bool";
+      } else {
+        try {
+          Integer.parseInt(defaultValue);
+          sb.append("int>   ");
+          type = "int";
+        } catch (NumberFormatException e) {
+          sb.append("string>");
+          type = "string";
+        }
+      }
+
+      sb.append(" - ");
+
+      if (name != null) {
+        sb.append(name.value());
+      } else {
+        sb.append(field.getName());
+      }
+
+      if (description != null) {
+        sb.append(": ").append(description.value());
+      }
+
+      if (type != null) {
+        sb.append(" (default: ");
+        switch (type) {
+          case "bool":
+            sb.append(defaultValue.equals("1"));
+            break;
+          case "int":
+            sb.append(defaultValue);
+            break;
+          case "string":
+            sb.append('"').append(defaultValue).append('"');
+            break;
+        }
+        sb.append(")");
+      }
+
+      System.out.println(sb);
+    }
+  }
+}