The following changes should fix real and potential problems
regarding how variables are set from function return values.
In assign from call expressions, Values in caller frame are now
directly assigned from function calls (call(), binCall() or builtins).
The assignement is performed with reflect Set methods or variants,
instead of "=" operator, to enforce runtime type checks.
The assignX() and assignX2() builtins are now removed in favor of
above method.
The representation of nil for pointer on struct has been fixed.
The identification of channel is fixed in for-range channel expression.
Catch illegal combinations for all binary operators.
Memoize type conversion to reflect.type.
Add some unit tests for arithmetic and assign operations.
* feat: add support for named output variables
Function output parameters are located at the start of the function
frame, uninitialized, as they could be only set through return
statements.
Supporting named output variables requires to:
- identify and allocate symbols corresponding to output names:
done at ident parsing, with the funcRet() helper,
- compute the location of output name in the frame:
done with retRank() helper,
- initialize the frame entry with the zero value of symbol type,
as the symbol can be accessed and written at multiple times,
and return not setting the variable (opposite to unnamed).
Done with frameType() helper, which now takes into account
output parameters.
* refactor: simplify memory management
Perform function frame analysis at pre-order, instead of post-order, to
initialize memory frame, and track value types. Remove all operation
involving unitialized types. Frame memory layout is now build
incrementally, instead of having to perform dedicated tree walks on AST.
Add an iString() type helper function, and use it to define the correct
conversion value prior to compare. The correction is to be applied to all
comparison operators, so regenerate op.go.
