Revision as of 23:58, 4 January 2018

Planning page for JDT Implementation of Local Variable Type Inference (JEP 286) for Photon (4.8)

Main tracking bug: JEP286 Bug

Compiler changes

Changes regarding the compiler: Compiler Bug

Grammar changes

Since var is not a keyword, but a reserved type name AND we need to be backwards compatible anyway, it should be handled in type resolution instead of grammar. Local variable type inference should be denoted by a bit AST node and type binding.

Type checking

• Determine the type of the var declaration
• Determine upwards/downwards type projection for type
• Fallback to "Object" type in case of error

Error reports

• Errors where local variable type cannot be inferred:
  • Cannot use 'var' on variable without initializer
  • Lambda expression needs an explicit target-type
  • Variable initializer is 'null'
  • Inferred type is non denotable
  • When method reference needs an explicit target-type.
  • array initializer needs an explicit target-type
• Error when defining a type called 'var':

This should be a configurable 'warning'/'info' for Java 9 and earlier.

Code generation

Shouldn't be much work since the stack frame would be filled in with the bound type anyway.

Java Search support

Changes regarding the Search: Search Bug

DOM support

Changes regarding the DOM: DOM Bug

UI Changes

This hasn't been looked into yet. Some ideas:

Code hover

• Show inferred type of variable

Preferences

• 'Code Style' option to prefer 'var' over specific types (to control the irritants generated by the compiler)

Quick fixes

• Convert 'var' into the resolved type
• Convert explicit typed local variable into 'var', like changing "String coolIde = "Eclipse";" into "var coolIde = "Eclipse";"
• Convert diamond operator to var, like fixing "List<String> names = new LinkedList<>()" into "var names = new LinkedList<String>()"

Code templates

• Use 'var' in templates for loops and introduce new variable, if preferred by the code style.