Decompiler (Rhino)
Date: 2018-10-23

org.mozilla.javascript

## Class Decompiler

- java.lang.Object
- - org.mozilla.javascript.Decompiler

-     public class Decompiler
      extends java.lang.Object

  The following class save decompilation information about the source. Source information is returned from the parser as a String associated with function nodes and with the toplevel script. When saved in the constant pool of a class, this string will be UTF-8 encoded, and token values will occupy a single byte. Source is saved (mostly) as token numbers. The tokens saved pretty much correspond to the token stream of a 'canonical' representation of the input program, as directed by the parser. (There were a few cases where tokens could have been left out where decompiler could easily reconstruct them, but I left them in for clarity). (I also looked adding source collection to TokenStream instead, where I could have limited the changes to a few lines in getToken... but this wouldn't have saved any space in the resulting source representation, and would have meant that I'd have to duplicate parser logic in the decompiler to disambiguate situations where newlines are important.) The function decompile expands the tokens back into their string representations, using simple lookahead to correct spacing and indentation. Assignments are saved as two-token pairs (Token.ASSIGN, op). Number tokens are stored inline, as a NUMBER token, a character representing the type, and either 1 or 4 characters representing the bit-encoding of the number. String types NAME, STRING and OBJECT are currently stored as a token type, followed by a character giving the length of the string (assumed to be less than 2^16), followed by the characters of the string inlined into the source string. Changing this to some reference to to the string in the compiled class' constant pool would probably save a lot of space... but would require some method of deriving the final constant pool entry from information available at parse time.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `CASE_GAP_PROP` Decompilation property to specify identation offset for case labels.
    `static int` | `INDENT_GAP_PROP` Decompilation property to specify default identation offset.
    `static int` | `INITIAL_INDENT_PROP` Decompilation property to specify initial ident value.
    `static int` | `ONLY_BODY_FLAG` Flag to indicate that the decompilation should omit the function header and trailing brace.
    `static int` | `TO_SOURCE_FLAG` Flag to indicate that the decompilation generates toSource result.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Decompiler()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static java.lang.String` | `decompile(java.lang.String source, int flags, UintMap properties)` Decompile the source information associated with this js function/script back into a string.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### ONLY_BODY_FLAG

          public static final int ONLY_BODY_FLAG

      Flag to indicate that the decompilation should omit the function header and trailing brace.
      See Also:
        Constant Field Values

    - #### TO_SOURCE_FLAG

          public static final int TO_SOURCE_FLAG

      Flag to indicate that the decompilation generates toSource result.
      See Also:
        Constant Field Values

    - #### INITIAL_INDENT_PROP

          public static final int INITIAL_INDENT_PROP

      Decompilation property to specify initial ident value.
      See Also:
        Constant Field Values

    - #### INDENT_GAP_PROP

          public static final int INDENT_GAP_PROP

      Decompilation property to specify default identation offset.
      See Also:
        Constant Field Values

    - #### CASE_GAP_PROP

          public static final int CASE_GAP_PROP

      Decompilation property to specify identation offset for case labels.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### Decompiler

          public Decompiler()

  - ### Method Detail

    - #### decompile

          public static java.lang.String decompile(java.lang.String source,
                                   int flags,
                                   UintMap properties)

      Decompile the source information associated with this js function/script back into a string. For the most part, this just means translating tokens back to their string representations; there's a little bit of lookahead logic to decide the proper spacing/indentation. Most of the work in mapping the original source to the prettyprinted decompiled version is done by the parser.
      Parameters:
        `source` - encoded source tree presentation
        `flags` - flags to select output format
        `properties` - indentation properties