nsgenbind
nsgenbind

This is a tool to generate JavaScript to DOM bindings from w3c webidl files and a binding configuration file.

Building

The tool requires bison and flex as pre-requisites

Commandline

nsgenbind [-v] [-n] [-g] [-D] [-W] [-I idlpath] inputfile outputdir

-v The verbose switch makes the tool verbose about what operations it is performing instead of the default of only reporting errors.

-n The tool will not generate any output but will perform all other operations as if it was. Useful for debugging bindings

-g The generated code will be augmented with runtime debug logging so it can be traced

-D The tool will generate output to allow debugging of output conversion. This includes dumps of the binding and IDL files AST

-W This switch will make the tool generate warnings about various issues with the binding or IDL files being processed.

-I An additional search path may be given so idl files can be located.

The tool requires a binding file as input and an output directory in which to place its output.

Debug output

In addition to the generated source the tool will output several debugging files with the -D switch in use.

interface.dot

The interfaces IDL dot file contains all the interfaces and their relationship. graphviz can be used to convert this into a visual representation which is sometimes useful to help in debugging missing or incorrect interface inheritance.

Processing the dot file with graphviz can produce very large files so care must be taken with options. Some examples that produce adequate output:

classical tree

dot -O -Tsvg interface.dot

radial output

twopi -Granksep=10.0 -Gnodesep=1.0 -Groot=0009 -O -Tsvg interface.dot

Web IDL

The IDL is specified in a w3c document[1] but the second edition is in draft[2] and covers many of the features actually used in the whatwg dom and HTML spec.

The principal usage of the IDL is to define the interface between scripts and a browsers internal state. For example the DOM[3] and HTML[4] specs contain all the IDL for accessing the DOM and interacting with a web browser (this not strictly true as there are several interfaces simply not in the standards such as console).

The IDL uses some slightly strange names than other object orientated systems.

IDL | JS | OOP | Notes --------—+---------------—+-------------—+-------------------------— interface | prototype | class | The data definition of | | | the object constants | read-only value | class variable | Belong to class, one copy | property on the | | | prototype | | operation | method | method | functions that can be called attribute | property | property | Variables set per instance --------—+---------------—+-------------—+-------------------------—

Binding file

The binding file controls how the code generator constructs its output. It is deliberately similar to c++ in syntax and uses OOP nomenclature to describe the annotations (class, method, etc. instead of interface, operation, etc.)

The binding file consists of three types of element:

binding

The binding element has an identifier controlling which type of
 output is produced (currently duk_libdom and jsapi_libdom).

The binding block may contain one or more directives which
 control overall generation behaviour:

webidl

    This takes a quoted string which identifies a WebIDL file to
     process. There may be many of these directives as required
     but without at least one the binding is not very useful as
     it will generate no output.

preface

    This takes a cdata block. There may only be one of these per
     binding, subsequent directives will be ignored.

    The preface is emitted in every generated source file before
     any other output and generally is used for copyright
     comments and similar. It is immediately followed by the
     binding tools preamble comments.

prologue

    This takes a cdata block. There may only be one of these per
     binding, subsequent directives will be ignored.

    The prologue is emitted in every generated source file after
     the class preface has been generated. It is often used for
     include directives required across all modules.

epilogue

    This takes a cdata block. There may only be one of these per
     binding, subsequent directives will be ignored.

    The epilogue is emitted after the generated code and the
     class epilogue

postface

    This takes a cdata block. There may only be one of these per
     binding, subsequent directives will be ignored.

    The postface is emitted as the very last element of the
     generated source files.

class

The class controls the generation of source for an IDL interface
 private member variables are declared here and header and
 footer elements specific to this class.

Although not generally useful, because methods that reference a
 class cause it to be implicitly created, empty definitions are
 permitted.

private

    variables added to the private structure for the class.

preface

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The preface is emitted in every generated source file after
     the binding preface and tool preamble.

prologue

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The prologue is emitted in every generated source file after
     the binding prologue has been generated.

epilogue

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The epilogue is emitted after the generated code and before
     the binding epilogue

postface

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The postface is emitted after the binding epilogue.

methods

The methods allow a binding to provide code to be inserted in
 the output and to control the class initializer and finalizer
 (note not the constructor/destructor)

All these are in the syntax of:

    methodtype declarator ( parameters )

They may optionally be followed by a cdata block which will be
 added to the appropriate method in the output. A semicolon may
 be used instead of the cdata block but this is not obviously
 useful except in the case of the init type.

methods and getters/setters for properties must specify both
 class and name using the c++ style double colon separated
 identifiers i.e. class::identifier

Note: the class names must match the IDL interface names in the
 binding but they will almost certainly have to be translated
 into more suitable class names for generated output.


preface

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The preface is emitted in every generated source file after
     the binding preface and tool preamble.


prologue

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The prologue is emitted in every generated source file after
     the binding prologue has been generated.


epilogue

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The epilogue is emitted after the generated code and before
     the binding epilogue


postface

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

    This takes a cdata block. There may only be one of these per
     class, subsequent directives will be ignored.

    The postface is emitted after the binding epilogue.


init

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

    TODO: should it become necessary to defeat the automated
     generation of an initializer altogether the identifier can
     be checked and if set to the class name (like a
     constructor) output body simply becomes a verbatim copy of
     the cdata block.

    The parameter list may be empty or contain type/identifier
     tuples. If there is a parent interface it will be called
     with the parameters necessary for its initializer, hence the
     entire ancestry will be initialised.

    The parameters passed to the parent are identified by
     matching the identifier with the parents initializer
     parameter identifier, if the type does not match a type
     cast is inserted.

    It is sometimes desirable for the parent initializer
     identifier to be different from the childs identifier. In
     this case the identifier may have an alias added by having
     a double colon followed by a second identifier.

    For example consider the case below where HTMLElement
     inherits from Element which inherits from Node.

      init Node("struct dom_node *" node);
      init Element("struct dom_element *" element::node);
      init HTMLElement("struct dom_html_element *" html_element::element);

    The three initializers have parameters with different
     identifiers but specify the identifier as it appears in
     their parents parameter list. This allows for differing
     parameter ordering and identifier naming while allowing the
     automated enforcement of correct initializer calling
     chains.


fini

    The declarator for this method type need only identify the
     class (an identifier may be provided but will be ignored).

   The cdata block is output.

   The parent finalizer is called (finalizers have no parameters
    so do not need the complexity of initializers.

method

    The declarator for this method type must contain both the
     class and the identifier.

    The cdata block is output.

getter

    The declarator for this method type must contain both the
     class and the identifier.

    The cdata block is output.

setter

    The declarator for this method type must contain both the
     class and the identifier.

    The cdata block is output.

Generated source

duk_libdom

This binding type generates several files as output:

References

[1] http://www.w3.org/TR/WebIDL/ [2] https://heycam.github.io/webidl/ [3] https://dom.spec.whatwg.org/ [4] https://html.spec.whatwg.org/