Implement new XML support

[hasithaa]

This issue create to track implementation progress of new proposed XML design ballerina-platform/ballerina-spec#288

Rough Implementation Direction,

Compiler front end

• Current Java-based version - No changes required. We already create AST nodes for the XML literal expression using the ANTLR-generated lexer and the parser.
• New compiler front end (will be written in Ballerina). We will write the scanner and the parser bits that identify and create AST nodes for the XML literal expression.

Ballerina compiler JVM back end

• We are using Axiom at the moment here now. To implement the runtime support for the new XML spec, we will replace Axiom with a custom XML tree with a customer tree builder written on top of StAX. Since this is JVM runtime, we will have to use Java here.

Ballerina compiler LLVM back end

• We are not yet clear about this implementation. But, most probably, we will have to implement the XML runtime support in C++ or Rust.

Related issues

• Not all charactors allowed from XML spec as nameChar are not supported in Ballerina grammer #14261 Not all charactors allowed from XML spec as nameChar are not supported in Ballerina grammer
• XML access expressions are not defined in the 2019R3 Spec #18875 XML access expressions are not defined in the 2019R3 Spec
• XML namespace declarations should be in scope only in the source part in which they occur, as with import declarations. #19384 XML namespace declarations should be in scope only in the source part in which they occur, as with import declarations.
• [Spec Deviation] lang.xml module contains functions not defined in the spec #18870 ballerina/lang.xml module contains functions not defined in the spec

Sub tasks

• Implement Table to XML convertion/datasource #19910 Implement Table to XML convertion/datasource

• Implement/fix JSON to XML converter #19941 Implement/fix JSON to XML converter

• Enable disabled test case XMLSecurityTest #19944 Enable disabled test case XMLSecurityTest

• Add test cases to cover xml value equalancy #19947 Add test cases to cover xml value equalancy

• Migrate XML tests to use JVM values instead of BVM values. #20064 Migrate XML tests to use JVM values instead of BVM values.

• Implement langlib.xml functions to support new xml proposal. #20666 Implement langlib.xml functions to support new xml proposal

• Implement new XML navigation syntax #20667 Implement new XML navigation syntax

• Validate xml atttribute names and element names to be within allowed charactors acording to w3 xml  #20670 Validate xml atttribute names and element names to be within allowed charactors acording to w3 xml

• Align XML attibute access with the XML proposal #20879 Align XML attibute access with the XML proposal

• Add XML element name expression #20880 Add XML element name expression

• XML attribute access is Lax #21102 XML attribute access is Lax

• Implement cycle detection in XML #21129 Implement cycle detection in XML

After 1.2.0

• Method invocations in XML step expressions are not aligned with the spec. #22136 Method invocations in XML step expressions are not aligned with the spec

• XML iterator need to be update to return xml #22135 XML iterator need to be update to return xml

• Issues with XML subtypes #22069 Support XML sequence constraint type

• XML index access using string index should be deprecated #22053 XML index access using string index should be deprecated

• XML literal should be able to directly declare XML named subtypes. #22155 XML literal should be able to directly declare XML named subtypes

• Remove dependency on Axiom library as Ballerina xml no longer depend on it #22151 Remove dependency on Axiom library as Ballerina xml no longer depend on it

• XML iterator still returns xml|string this should be just xml #24562 XML iterator still returns xml|string this should be just xml

[hasithaa]

Closing this issue, since XML support has been added and, remaining individual tasks are captured in separate issues.