I have a project in Eclipse where I have an editor for a custom language. I am using ANTLR to generate the compiler for it. What I need is to add content assist to the editor.
The input is a source code in the custom language, and the position of the character where the user requested content assist. The source code is most of time incomplete as the user can ask for content assist any time. What I need is to calculate the list of possible tokens that are valid for the given position.
It is possible to write a custom code to do the calculation, but that code would have to be manually kept in sync with the grammar. I figured the parser is doing something similar. It has to be able to determine at a given context what are the acceptable tokens. Is it possible to "reuse" that? What is the best practice in creating content assist anyway?
Thanks,
Balint
Have a look at Xtext. Xtext uses Antlr3 under the hood and provides content assist for the Antlr based languages. Have a look especially into package org.eclipse.xtext.ui.editor.contentassist.
You may consider to redefine your grammar with Xtext, which would provide the content assist out-of-the-box. It is not possible to reuse the Antlr grammar of a custom language.
Related
I want to make a plugin for a language for the Intellij Idea IDE. The language has been developped using Eclipse Xtext and is open source. A plugin already exists for Eclipse.
My goal is to port this language to Intellij Idea. I want to be able to use Intellij to create source files, to have the specific syntax highlighting and to be able to compile and run programs written with this language.
Is there a simple way to generate the Intellij Idea plugin using the Xtext project?
If not is there an efficient solution to be able to have the specific syntax highlighting in Intellij? (an automatic way if possible, I would prefer not rewriting everything everytime the Xtext project is updated)
Short answer
Yes, with a bit of work.
Long Answer
Sadly, Xtext uses antlr in the background and IntelliJ use their own grammar kit based on Parsing Expression Grammars. As such, the parsing and editor code generated by XText, as you might have guessed, will not work.
In order to get your language working in IntelliJ you will need to:
Create grammar *.bnf file
Generate lexer *.flex file, possibly tweak it and then run JFlex generator
Implement helper classes to provide, among others, file recognition via file extension, syntax highlighting, color settings page, folding, etc.
The *.flex file is generated from the bnf. Luckily, most of the classes in step 3 follow a very similar structure so they can be easily generated (more on that later). So basically, if you manage to generate the *.bnf file, you are 80% there.
Although from different technologies, the syntax of bnf files is very similar to XText files. I recently migrated some antlr grammars to IntelliJ's bnf and I had to do very small changes. Thus, it should be possible to autogenerate the bnf files from your XText ones.
That brings me back to point 3. Using XTend, Epsilon's EGL, or similar, it would be easy to generate all the boiler plate classes. As part of the migration I mentioned before I also did this. I am in the process of making the code public, so I will post it here when done and add some details.
I am wondering if I can generate ANTLR grammar from java source code. I want to do some kind of research project, but I am just exploring different open sources to see which one is best.
For ANTLR, do I always have to write a grammar and pass it to the ANTLR?
Is there a way to generate grammar from an existing Java source code?
Not easily. ANTLR generate a recursive descent parser from your grammar, encoding the tests into procedural code, as well as lots of other bookkeeping stuff.
Knowing how the code is generated, you might be able to take it apart but you'll have to reach into the middle of generated statements and that isn't easy without a full parser for the generated language. (Hint: regex won't work).
I don't see a lot of point of this exercise. Why don't you just use the original grammar?
If I have an AST and modify it, can I use StringTemplates to generate the source code for the modified AST?
I have successfully implemented my grammar for Antlr4. It generates the AST of a source code and I use the Visitor Class to perform the desired actions. I then modify something in the AST and I would like to generate the source code for that modified AST. (I believe it is called pretty-printing?).
Does Antlr's built in StringTemplates have all the functionality to do this? Where should one start (practical advice is very welcome)?
You can walk the tree and use string templates (or even plain out string prints) to spit out text equivalents that to some extent reproduce the source text.
But you will find reproducing the source text in a realistic way harder to do than this suggests. If you want back code that the original programmer will not reject, you need to:
Preserve comments. I don't think ANTLR ASTs do this.
Generate layout that preserves the original indentation.
Preserve the radix, leading-zero count, and other "format" properties of literal values
Renerate strings with reasonable escapes
Doing all of this well is tricky. See my SO answer How to compile an AST back to source code for more details. (Weirdly, the ANTLR guy suggests not using an AST at all; I'm guessing this is because string templates only work on ANTLR parse trees whose structure ANTLR understands, vs. ASTs which are whatever you home-rolled.)
If you get all of this right, what you are likely to discover is that modifying the parse tree/AST is harder than it looks. For almost any interesting task on complex languages, you need information which is not trivial to extract from the tree (e.g., what is the meaning of this identifier?, where is this variable used?,...) I call this the problem of Life After Parsing. My main point is that it takes a lot of machinery to modify ASTs and regenerate code; be aware of the size of your project.
I am creating a custom language plugin for IntelliJ.
I would like it to be possible for a file in the new language to contain fragments of text in other languages.
The specific languages I would like to support are HTML, JS, CSS, and SQL.
I would also like to support other custom languages (i.e. languages I would define the syntax for).
The main feature I want is syntax coloring, but if I can get stuff like "go to declaration" and refactoring out of the box then all the better.
My last requirement is that it would be possible to use my own code to tell IntelliJ which language a fragment contains; fragments containing different languages will not be distinguishable at the lexer / parser level.
In short, I would like to implement something similar to what PhpStorm does when it detects, say, SQL inside a string:
I looked at IntelliJ's source code and found the ILazyParseableElementType interface which seemed relevant, but I'm not sure if this is the way to go (and if so - how to use it in my code exactly...)
Any pointers would be highly appreciated...
The Intellij feature/terminology you are looking for is Language Injections.
Here is a github PR which implements a very similar feature for JFLex files.
In short you need to implement a LanguageInjector and add it to your plugin.xml as a <languageInjector implementation="YourImplClass">.
I've recently developed a domain-specific language using flex and bison. I would like to create a user interface for editing script files using this language. In particular I would like to have common functionalities such as file handling, menus, buttons, syntax highlighting, error checking and so on. Do you know any tool which can be used to develop such kind of application? I would prefer one which can give me a prototype rapidly.
such as file handling, menus, buttons, syntax highlighting, error
checking
I think that file handling, menus, buttons and highlighting are your least concerns. What you call "error checking" on the other hand. That can be a tough nut. I will try to give you some pointers to how you can (in a somewhat primitive manner) detect errors on the fly as the user inputs source code in the editor.
I assume you wish for something like Eclipses (for java at least) real time analysis of the written code in the editor? I'm not familiar with how Eclipse work internally but this is probably done by some pre-compilation process that processes all source code again and again as you change it.
One way to prototype this (and indeed build a non-prototype as well) would be to use Flex and Bison, and I notice you already is familiar with these tools. You can build you grammar and create action code for all interesting parts so you can find syntax deviations fairly easy. After this you make your editor run the flex and bison generated c-code as the user writes the source code in you IDE and have some way of displaying the output. Either in a terminal-like status window or directly in the text-editing field (as Eclipse does) (the latter case is probably a pain to build but by no means impossible and would give you IDE a professional touch).
Suppose you would like to build an IDE for ADA 95 the following Flex and Bison (Actually Lex and Yacc) code could help you do exactly this (it's a decent syntax analyzer that reports errors (what and where)):
http://www.adaic.org/resources/add_content/standards/95lrm/lexer9x.l
http://www.adaic.org/resources/add_content/standards/95lrm/grammar9x.y
Hope this helps.
Edit:
to have cool error highlighting and such in the text-editor field of your IDE you could let your bison generated syntax analyser generate something thats easy to parse, like XML, that contains the type of error and where it lies (row and column for example) and then use that to display the errors... you simply embed an XML parser in the IDE (lots of free one available) and extract the data you need and change the display accordingly... That shouldn't be rocket science when I think about it.