Toy v1 parser implementation

[rturrado]

ANTLR 2: visitors, error listeners

This is the second task on the cQASM 3.0 roadmap after the Toy v1 infrastructure (see PR #157).
It has allowed us to focus purely on implementing a minimal ANTLR parser without touching other aspects of the language.

The cqasm-parse-helper API:

• creates a ScannerAntlr that receives a BuildCustomAstVisitor and a CustomErrorListener, and then
• creates a ParseHelper that receives a ScannerAdaptor.

The ScannerAntlr class:

• parses an input stream to an ANTLR AST, and
• builds a tree-gen AST out of this ANTLR AST.

The ParseHelper class:

• invokes the ScannerAntlr to parse an input stream, and, whether,
• returns the tree-gen AST without errors, or
• catches any parsing exception and returns a null AST with some errors.

Things we don't want in develop

• res/v1x/test-v1x-parsing: I needed something to test against. However all those tests will be lost....
• cqasm-analyzer.{hpp,cpp}, cqasm.{hpp,cpp}, cqasm-py.{hpp,cpp}: I've removed the analyze functions that received only a file name or a data string from the Analyzer. This way, at a higher level, at cqasm.hpp or cqasm.py.hpp, I can call the Analyzer with a v1 or v3 parser. I.e. we can reuse the v1 Analyzer for the v3 parser. I understand we won't want this functionality in the future.

Things we do want in develop

• Changes to v1x parser:
  • Moved ParseResult to a separate file.
  • MInor aesthetic changes, like removing ../ from an include header when unnecessary.
• Changes to v3x parser:
  • Implementation of ParseHelper, build tree-gen AST visitor, custom error listener...
  • generate_antlr_parser.py: added a parameter to generate a base visitor class.
  • Cqasm{Lexer,Parser}.g4: renamed cqasm_lexer.g4 and cqasm_parser.g4 to CqasmLexer.g4 and CqasmParser.g4 as these texts are used as class names, and all ANTLR class names are written in camel case.
  • CqasmParser.g4: renamed expressions from snake case to camel case (for the same reason as above).
• test/v1x/parsing.cpp:
  • Removed dirent.h dependency. Used std::filesystem instead.
  • Fixed version comparison code?
• Use of fmt::format instead of standard streams in many places.
• Better naming. For example flie_name instead of filename, or file_path instead of file_name when the variable actually holds a path.

TODO

• Semantic checks: try enabling them in parsing.cpp for v3x. Also, see if they would require some changes in ANTLR.
• ParseResult: try changing ParseHelper so that it works with an interface containing a pointer to a generic AST, not to a tree-gen AST.
• test/v1x/parsing.cpp: Is version > cqasm::version::Version("1.2") working properly?

[pablolh]

Wow!

[rturrado]

Hi Pablo,

I think I have addressed most of your comments. We still have to talk about what we want in develop from this PR:

• There are things here that are completely unrelated to the Toy v1 implementation and could be merged into develop.
• Other things, such as the current ANTLR grammar, or the tests, may go in but just considering that they would be soon rewritten for the MVP implementation.