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Naveen Naidu

GSOC - Handle Nested Languages Overview

gsoc7 min read

Hola Amigos!

The Coding Phase - 1 of GSoC has started and it has been pretty fun. I also have my University Finals going on now. They'll end on July 3rd. Banglore does live in a different kind of world :P - Phew! This is a really busy month. I have to manage Finals, GSoC and Open Mainframe Internship cocurrently. I like this kind of atmosphere though. It keeps me on my toes and pushes me to break my own boundaries and limits that I so absent mindedly set upon on myself. And it's pretty damn fun.

There's a different craze - The adrenaline that rushes through your body, when you put on your headphones, and sit infront of your laptop to code and learn lot's of new stuff everyday. It's finger licking good (EWWW! You can come with better exclamation Naveen :facepalm:). There has been a lot of Aha! moments until now as well. And some moments where I felt like hitting Anne so hard that all her teeths come out. Oh! For the unintiated - Anne is the name of my Laptop. She's so fucking good. Especially when the red color light's her body up. Alright! I won't go on about Anne more - Else it would get more intimate :speak_no_evil: But all in all - Anne is a good girl and she's mine. So People! Keep your hands of her - It's pretty well encrypted anyways - You won't be able to get any fun just by laying your hands on it. Hehehe!

Ah! Here it is again. I shifted from the topic - And I'm too lazy to go back and erase it up. So I'll let that be there anyway.

Coming back to the point! This post is to introduce you(you - as in the bots of the internet) about What my project is? and A brief Overview of the project.

The title of my project is Handle Nested languages.

The proposal for this project is present here


coala in its present state is capable of providing efficient static analysis to only those file that contains a single programming language. But Multiple programming languages can coexist in a single source file.Eg: PHP and HTML , HTML and Jinja , Python and Jinja , codeblocks and RST etc.

coala does not yet support these kind of files. This project would enable coala to deal with those situations and allow people to write code analysis similar to how they already do it while being applicable to the right locations at the right files.The users of coala would not have to concentrate on writing new bears/ analysis routines. This implementation would perfectly work with the existing bears.

There can be several ways to approach this. In this cEP, we will be implementing a abstract way which will support arbitrary combination of languages.

A higher level view of the implementation

A source file containing multiple programming languages is loaded up by coala. The original nested file is broken/split into n temporary files, where n is the number of languages present in the original file. Each temporary file only contains the snippets belonging to one language.

These temporary files would then be passed to their respective language bears ( chosen by the user) where the static analysis routines would run. The temporary files after being linted would then be assembled.

The above process creates the illusion that the original file is being linted, but in reality we divide the files into different parts and lint them one by one.

The figure below, would help give a clear picture


Nested Language Section (nl_section)

The original file is segregated into small pieces/units where each piece/unit purely contains only one language. These quantum pieces of the the nested original file is termed as nl_section.

A nl_section can further be defined as a group of lines in the source code that purely belongs to one particular language.

All the nl_sections that belong to one particular language are grouped to form a valid file of that programming language.

The following figure would make the things clear


In the above figure, we have a file which contains both HTML and PHP code. This original file can be broken up into 4 different sections.

Each nl_section will contain the following information:

  1. The Programming language of the lines
  2. Index of the section
  3. Starting Line number in the original file
  4. Ending Line number in the original file
  5. Starting line number in the linted file
  6. Ending line number in the linted file

Prototype of nl_section

1class NlSection(TextRange):
3 def __init__(self,
4 orig_start: NlSectionPosition,
5 orig_end: (NlSectionPosition, None) = None,
6 index=None,
7 language=None):
8 """
9 Creates a new NlSection.
11 :param orig_start: A NlSectionPosition indicating the start of the
12 section in original file.
13 :param orig_end: A NlSectionPosition indicating the end of the
14 section in the original file.
15 If ``None`` is given, the start object will be used
16 here. end must be in the same file and be greater
17 than start as negative ranges are not allowed.
18 :param language: The programming language of the lines.
19 :param index: The index of the nl_section.
20 :raises TypeError: Raised when
21 - start is not of type NlSectionPosition.
22 - end is neither of type NlSectionPosition, nor
23 is it None.
24 :raises ValueError: Raised when file of start and end mismatch.
25 """
26 TextRange.__init__(self, start, end)
27 self.index = index
28 self.language = language
30 """
31 :linted_start: The start of the section in the linted file.Initially it
32 is same as that of the start of the original file. It
33 changes only when any patches are applied on that line.
34 :linted_end: The end of the section in the linted file.Initially it
35 is same as that of the end of the original file. It
36 changes only when any patches are applied on that line.
37 """
38 self.linted_start = start
39 self.linted_end = end
41 if self.start.file != self.end.file:
42 raise ValueError('File of start and end position do not match.')
44 @classmethod
45 def from_values(cls,
46 file,
47 start_line=None,
48 start_column=None,
49 end_line=None,
50 end_column=None,
51 index=None,
52 language=None):
53 start = NlSectionPosition(file, start_line, start_column)
54 if end_line or (end_column and end_column > start_column):
55 end = NlSectionPosition(file, end_line if end_line else start_line,
56 end_column)
57 else:
58 end = None
60 return cls(start, end, index, language)


The implementation of the nested language architecture would be done inside the a new folder called as nestedlib . This nestedlib would be present under the coalib directory.


The following figure depicts the architecture that is going to be implemented to enable nested languages support.


  • NLCore

This is the heart of the project. It is responsible to manage the execution flow in the program

  • NLInfoExtractor

NLInfoExtractor is responsible to extract the information from the user's input. The extracted information would include the languages present in the file, bears to run for each programming language and the settings of these bears.

  • Parser

Parser splits up the original nested file into different nl_sections.

  • NLFileHandler

NL FileHandler is responsible for creating the temporary files (which contains all the sections belonging to a single language) that would be passed for the actual analysis.


This project will be implemented in four phases:

  • Information Gathering
  • Segregating the file
  • Linting the file
  • Assembling

Phase 1: Information Gathering

The users can inform coala about the presence of nested languages in the files using the --handle-nested flag.


1coala --handle-nested --files=html_php_file.html --language=html,php --bears=HTMLBear,PHPBear
  • --languages: Informs coala about the languages present in the file
  • --bears: Informs coala about the bears to run on the file.

The aim of information gathering is to extract the following information from the arguments passed to coala:

  1. Languages present in the file
  2. Language and Bear association
  3. Argument list (would be used to create coala sections)

The languages present in the file can easily be gathered from the --language tag. The language and Bear association information can be attained by using the meta information of the bear and matching it with the --languages.

NlInfoExtractor is responsible for the above tasks.

The original nested language file is divided into various temporary in-memory files, where each file contains the snippets of one particular language. The linting needs to be done by the respective bears on each of the file.

In order to do so, we would have to create virtual coala sections for each file.

Each section, would contain the information about the files to be linted, the bears to run on those files and the setting to initialize the bear with. In order to create these sections we would need the arguments to be passed to the parse_cli() method. The arguments used to initialize coala in nested language mode cannot be used to create the coala sections.

The NlInfoExtractor converts the original arguments into different argument list, where each argument list resembles the argument that a user would have passed if he was linting a single temp_file with the appropriate bears.

For eg:

1coala --handle-nested --file=html_php_file.html --language=html,php --bears=HTMLBear,PHPBear

gets converted to:

1coala --file=temp_html_file --language=html --bears=HTMLBear


1coala --file=temp_php_file --language=php --bears=PHPBear

The above arguments when passed to the parse_cli() method, creates two section:

2files = temp_html_file
3bears = HTMLBear
4setting = value
7files = temp_php_file
8bears = PHPBear
9setting = value Prototype

1def extract_info(args):
2 """
3 Return a dictionary called as `nl_info_dict` with all the extracted
4 information.
6 Let's assume that we have the following arguments
8 >>>args = coala --handle-nested --file=html_php_file.html --language=html,php --bears=HTMLBear,PHPBear
10 >>> nl_info_dict = extract_info(args)
12 >>> nl_info_dict
13 {
14 "file_name": html_php_file.html,
15 "absolute_file_path": /home/test/html_php_file.html,
16 "languages": [html, php]
17 "bears": [HTMLBear, PHPBear]
18 "language_bear_dict": language_bear_dict
19 "arg_dict": arg_dict
20 }
22 >>> nl_info_dict['language_bear_dict']
23 {
24 "html": [HTMLBear],
25 "php" : [PHPBear]
26 }
28 >>> nl_info_dict['arg_dict']
29 {
30 "nl.html": {"file_name": "temp_html_file",
31 "bears": 'HTMLBear',
32 "settings": [(setting,value)]
33 }
36 "nl.php": {"file_name": "temp_php_file",
37 "bears": 'PHPBear',
38 "settings": [(setting,value)]
39 }
41 }
44 """
46def get_lang_info(args):
47 """Return a list of langauges present in the nested file"""
49def get_bear_info(args):
50 """Return the list of bears to be run on the file"""
52def get_file_info(args):
53 """Returns the list of files to be linted"""
55def get_absolute_file_path(file_name):
56 """Returns the absolute file path of eacg file"""
58def get_language_bear_dict(languages, bears):
59 """
60 Return a language_bear dict, where each language is mapped to a set of bears
61 """
63def get_argument_dict(file_list, language_bear_dict, settings):
64 """
65 Returns a argument_dict, where each temp_file is mapped to a set of
66 arguments.
67 """

different nl_sections and creating temporary files for each nested languages, which would contain the snippets of that language from the original nested file.

This phase uses the Parser and the NlFileHandler parts of the architecture.

Phase 2: Segregation of Nested File


  • Parser is responsible for splitting the original file into different nl_sections.

  • The input and output to the parser is standardized, where the input to the parser are the contents of the original nested file and the output is the list of nl_sections encompassing the snippets of different programming language.

  • Standardizing the parser helps us in removing any restriction on how a parser should parse the contents. A parser can also use third party API's as long as the output from it is in accordance with the format of a nl_sections.

  • Since different combination of languages would need different parsers, we would create a new folder at nestedlib/parsers which would host the collection of all the parsers.

  • A new super class called as Parser would be created. This would have all the common methods that all the parser might need. All the parser would be derived from this Superclass. Prototype

1import coalib.nestedlib.NlSection
3class Parser:
5 def parse(file_contents):
6 '''
7 Returns a list of nl_sections.
9 :param file_contents: The contents of the original nested file
11 >>> file_contents = \
12 """
13 <!DOCTYPE html>
14 <head>
15 <title>Hello world as text</title>
16 <?php
17 echo "<p>Hello world</p>";
18 ?>
19 </html>
20 """
22 >>> p = Parser()
23 >>> nl_sections = p.parse(file_contents)
24 >>> nl_sections
25 ( <NlSection object(index=1, language=html, orig_start=1, orig_end=3)>,
26 <NlSection object(index=2, language=php, orig_start=4, orig_end=6)>,
27 <NlSection object(index=3, language=html, orig_start=7, orig_end=7)>
28 )
29 '''
31 def detect_language(str):
32 """
33 Return the language of the particulat string.
35 This will be overridden by the child class
36 """
38 def create_nl_section(start, end, language, index):
39 """
40 Creates a NlSection Object from the values.
42 Returns the NlSection object
43 """
45 return NlSection.from_values(start=start, end=end, language=language,
46 index=index)

Making temporary files

This sections deals with how the segregated section (nl_sections) from the parser are combined to form different temporary files on which linting will be done.

NlFileHandler is responsible to create the temporary files. These temporary files are stored in the memory.

  1. The nl_sections are passed to NlFileHandler.

  2. NlFileHander then creates a nl_file_dict, where the key is the name of the temporary file and the contents are it's value. It is similar to the file_dict that is created by coala in instantiate_process() during the execution of the section.

  3. It is important to keep in mind, that the temporary segregated file are not actually present in the folder. In the normal flow of coala,during the execution of the coala sections, coala will try to find the files by the filenames mentioned in the coala section. And then create a file_dict. That cannot happen in our case. So we will explicitly replace the file_dict with nl_file_dict. Prototype

1def get_nl_file_dict(nl_file_info, nl_sections):
2 """
3 Returns a nl_file_dict, where the key is the name of the temporary file
4 and the value is the contents of that file.
6 :param nl_file_info: The information extracted from the arguments.
7 This is generated by the NlInfoExtractor.
8 :param nl_sections: The segregated sections of the original file.
10 >>> nl_file_info
11 {
12 "file_name": html_php_file.html,
13 "absolute_file_path": /home/test/html_php_file.html,
14 "languages": [html, php]
15 "bears": [HTMLBear, PHPBear]
16 "language_bear_dict": language_bear_dict
17 "arg_dict": arg_dict
18 }
20 >>> nl_sections
21 ( <NlSection object(index=1, language=html, orig_start=1, orig_end=3)>,
22 <NlSection object(index=2, language=php, orig_start=4, orig_end=6)>,
23 <NlSection object(index=3, language=html, orig_start=7, orig_end=7)>
24 )
26 >>> file_contents = get_file(nl_file_info['file_name'])
28 >>> file_contents = \
29 '''
30 <!DOCTYPE html>
31 <head>
32 <title>Hello world as text</title>
33 <?php
34 echo "<p>Hello world</p>";
35 ?>
36 </html>
37 '''
39 >>> nl_file_dict = get_nl_file_dict(nl_file_info, nl_sections)
40 >>> nl_file_dict
41 {
42 "temp_html_file":('''<!DOCTYPE html>\n
43 <head>\n
44 <title>Hello world as text</title>\n
45 \n
46 \n
47 \n
48 </html>'''),
50 "temp_php_file":('''\n
51 \n
52 \n
53 \t\t<?php\n
54 \t\t\techo "<p>Hello world</p>";\n
55 \t?>''')
58 }
60 """
62def get_file_contents(file_name):
63 """ Returns the contents of the file"""
65def assemble(nl_diff_dict, nl_sections, nl_info_dict):
66 """
67 Assembles the temporary files.
69 The sections are extracted by their increasing order of their index and
70 then written directly to the original file.
71 """
72 file = open(nl_info_dict['absolute_file_path'], 'w')
74 for nl_section in sorted(nl_sections.index):
75 temp_file_name = nl_section.temp_file
76 start = nl_section.linted_start
77 end = nl_section.linted_end
78 linted_file_content = nl_diff_dict[temp_file_name]
80 section_content = get_file_content(linted_file_content, start, end)
82 file.write(section_content)

Phase 3: Linting the file

This phase deals with linting the temporary files created by the NlFileHandler using the nl_sections.

  1. In coala the linting of the files are done when the section created by coala are executed.

  2. Since we are explicitly making the sections for nested languages, care has been taken to keep the file names of the nl.lang section and the file names in nl_file_dict same.

  3. During the execution of the section, in the instantiate_process() we do not access the physical file, rather we replace the file_dict with nl_file_dict and make the necessary changes.

  4. Once the file_dict is changed, coala will normally continue the process. To coala, it now looks as if the temporary files were actually present in the physical drive. And the linting starts

Applying the Patches

Whenever the bears suggests a patch and the user desires to apply the Patch, we would also need to update the information of the linted_start and linted_end. This needs to be done because, whenever a patch is applied the position of the lines might change because of addition and deletion of lines.

Keeping track of the start and end of a particular nl_section in the linted files would help in easier extraction of the nl_section from the temporary created files.

In order to do so, we'll have to make changes to the apply() method of the ApplyAction. We use the update_nl_sections() functions to update the values.

In we add a new function get_diff_info() that would give us the information of the diff

1def get_diff_info():
2 """
3 Returns tuple containing line numbers of deleted,changed and added lines.
4 """
5 deleted_lines = []
6 added_lines = []
7 changed_lines = []
9 for line_nr in self._changes:
10 line_diff = self._changes[line_nr]
12 if line_diff.change:
13 changed_lines.append(line_nr)
14 elif line_diff.delete:
15 deleted_lines.append(line_nr)
16 if line_diff.add_after:
17 added_lines.append(line_nr)
19 return changed_lines, deleted_lines, added_lines

The following method belongs to the NlCore

1from coalib.result_action.Diff import stats,get_diff_info
3diff_stats = stats()
4diff_info = get_diff_info()
6def find_section_index(diff_stats, diff_info, nl_sections):
7 """
8 Returns the section index to which the patch is about to be applied.
9 """
11 return index
13def update_nl_sections(diff_stats, diff_info, nl_sections):
14 """
15 Updates the `linted_start` and the `linted_end` of the nl_sections
16 """
18 index = find_section_index(diff_stats, diff_info, nl_sections)
20 for nl_sections in nl_sections:
21 if nl_section.index == index:
22 """
23 Update the values of linted_start` and the `linted_end`
24 """

Phase 4: Assembling

This phase deals with assembling the linted temporary files back into the original file.

This phase has two parts:

  1. Extracting the sections from the linted temporary files.
  2. Assembling these sections.

Once all the coala sections have been executed, we have a nl_diff_dict where the key is the name of the temporary file and the value is the contents of the linted file contents of the temporary file.

We have a assemble() method inside the NlFileHandler, which uses the information from the nl_sections and extracts the sections from the nl_diff_dict and write it to the original file

1def assemble(nl_diff_dict, nl_sections, nl_info_dict):
2 """
3 Assembles the temporary files.
5 The sections are extracted by their increasing order of their index and
6 then written directly to the original file.
7 """
8 file = open(nl_info_dict['absolute_file_path'], 'w')
10 for nl_section in sorted(nl_sections.index):
11 temp_file_name = nl_section.temp_file
12 start = nl_section.linted_start
13 end = nl_section.linted_end
14 linted_file_content = nl_diff_dict[temp_file_name]
16 section_content = get_file_content(linted_file_content, start, end)
18 file.write(section_content) Prototype

1from coalib.nestedlib.NlInfoExtractor import extract_info
2from coalib.result_action.Diff import stats,get_diff_info
3from coalib.nestedlib.NlFileHandler import get_file_contents, get_nl_file_dict, assemble
5import coalib.nestedlib.Parser
7def get_arg_info(arg):
8 """
9 Return argument list and nl_info_dict that will be used to make
10 the coala sections
12 >>> arg_list = get_arg_list(arg)
13 [ ( (file, temp_html_file), (bears, HTMLBear ), (settings, value) ),
14 ( (file, temp_php_file), (bears, PHPBear ), (settings, value) )
15 ]
17 """
18 nl_info_dict = extract_info(arg)
19 arg_list = make_arg_list(nl_info_dict)
21 return nl_info_dict, arg_list
23def get_file_metadata(nl_info_dict):
24 """
25 Returns the nl_sections and nl_file_dict
26 """
28 parser = detect_parser(nl_info_dict['languages'])
29 file_contents = get_file_contents(nl_info_dict['absolute_file_path'])
31 index = find_section_index(diff_stats, diff_info, nl_sections)
33 for nl_sections in nl_sections:
34 if nl_section.index == index:
35 """
36 Update the values of linted_start` and the `linted_end`
37 """
40def assemble_files(nl_diff_dict, nl_sections, nl_info_dict):
41 """
42 Assembles the file and returns back to coala_main
43 """
45 return assemble(nl_diff_dict, nl_sections, nl_info_dict)

Changes in

1import coalib.nestedlib.Nlcore
2def main(debug=False):
3 configure_logging()
4 handle_nested = True
6 args = None # to have args variable in except block
7 # when parse_args fails
8 try:
9 args = default_arg_parser().parse_args()
10 if args.handle_nested:
11 nl_info_dict, nl_arg_dict = get_arg_info(args)
12 nl_sections, nl_file_dict = get_file_metadata(nl_info_dict)
14 """
16 Code Contents of of
18 """
20 return mode_normal(console_printer, None, args, debug=debug,
21 handle_nested, nl_info_dict, nl_arg_dict,
22 nl_sections, nl_file_dict)

That's it for now folk. Will update you soon as soon as I complete all my tasks of Coding Phase 1. All the best to me :grimacing: