json lazy parser unparser and support for reading NULL values.

[jurgenvinju]

• read and write JSON null values, every type can register its preferred null representation in Rascal. Maybe[&T] is also builtin supported
• read and write JSON str values as algebraic data-typed, by providing your own parsers/unparsers for specific data types
• accurate line/colum, offset/lengths for parse and validation errors
• tests for the above
• application of the above to the cytoscape.js bridge to improve the Rascal import graph visualization
• fix Json random test failed #2098

[codecov]

Codecov Report

Attention: Patch coverage is 38.92473% with 284 lines in your changes missing coverage. Please review.

Project coverage is 49%. Comparing base (043b663) to head (9380bf8).
Report is 52 commits behind head on main.

Files with missing lines	Patch %	Lines
...pl/library/lang/json/internal/JsonValueReader.java	35%	230 Missing and 36 partials ⚠️
...pl/library/lang/json/internal/JsonValueWriter.java	60%	4 Missing and 2 partials ⚠️
src/org/rascalmpl/library/lang/json/IO.java	76%	2 Missing and 1 partial ⚠️
src/org/rascalmpl/values/maybe/UtilMaybe.java	76%	3 Missing ⚠️
src/org/rascalmpl/library/util/TermREPL.java	0%	2 Missing ⚠️
src/org/rascalmpl/library/util/Webserver.java	0%	2 Missing ⚠️
src/org/rascalmpl/repl/REPLContentServer.java	0%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##              main   #1978    +/-   ##
========================================
  Coverage       49%     49%            
- Complexity    6317    6346    +29     
========================================
  Files          666     667     +1     
  Lines        59695   59836   +141     
  Branches      8670    8691    +21     
========================================
+ Hits         29600   29725   +125     
+ Misses       27863   27857     -6     
- Partials      2232    2254    +22     

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[jurgenvinju]

@tvdstorm I added the null values here. Do you fancy the solution?

[jurgenvinju]

Since this adds parameters to Java methods we have to wait until after the current release cycle to merge this.

[DavyLandman]

A lot of things are happening in this PR, and I'm missing:

• new tests for the functionality added.
• discussion on effect of existing json serialization (which we also depend on in VS Code)
• is Use parameter names to choose the right constructor for the JSON deserialization. #1984 also solved?

[DavyLandman]

The changes to JsonValueReader are hard to oversee, it mostly looks fine, but I would want to take some time and test the impact on VS Code and it's use of the JsonValueReader class.

[DavyLandman]

do we want this as part of this PR?

[jurgenvinju]

This is necessary for bootstrapping the tutor

[jurgenvinju]

still going to see if we can minimize the number of failing pages before merging.

[jurgenvinju]

The changes to JsonValueReader are hard to oversee, it mostly looks fine, but I would want to take some time and test the impact on VS Code and it's use of the JsonValueReader class.

The changes have been designed such that there can't be impact on existing uses of the JSON IO clients, unless they were waiting for NPEs for inputs with null inside. Those exceptions will not be thrown anymore and values will be constructed to represent those null values.

Recommend to focus on that distintion. Typically catch( NullpointerException e) in java or catch Java("NullpointerException") in Rascal.

[jurgenvinju]

The other changes are only activated by providing new actual keyword parameters to format datatypes to string or parse strings to datatypes. If not provided the code behaves as before.

[DavyLandman]

Is there a way to increase the test coverage? Only 35% of the added lines for the JSONReader are covered according to codecov.

[jurgenvinju]

Is there a way to increase the test coverage? Only 35% of the added lines for the JSONReader are covered according to codecov.

The reason is that the IO tests use the @deprecated JSON readers and writers. To change this we need to simply replace the reader by the new parser and the writer by the new unparser in the readWriteTest, but the new issues that come up are both very old and pretty diverse. I want to capture the fixes in a new PR.

"new" here is already 8 years (!!!), btw. It's really time to remove the deprecated functions and continue with the new ones