fix(cfc): generic variable type resolution

[volsa]

Problem: The CFC implementation for stateless functions creates "temporary" variables for their return and output variable values. For example bar := foo(in := localIn, acc => localOut) where foo returns a DINT value will transpile to

VAR
    bar: DINT;
    localOut: DINT;
    __out_foo_1: DINT;
    __out_acc_1: DINT;
END_VAR

__out_foo_1 := foo(in := localIn, acc => __out_acc_1);
bar := __out_foo_1;
localOut := __out_acc_1;

However, for generics this is a bit tricker because generic type resolution requires first a call site bevore its types can be derived. As such the transpiler up until now generated the following for the same foo example assuming now both the return and output values are a generic of type T: ANY_NUM:

VAR
    bar: DINT;
    localOut: DINT;
    __out_foo_1: __foo__T;
    __out_acc_1: __foo__T;
END_VAR

__out_foo_1 := foo(in := localIn, acc => __out_acc_1);
bar := __out_foo_1;
localOut := __out_acc_1;

These "generic variables" never resolved and yielded an error when compiling.

Solution: Introduce an "inference" module, which uses the existing TypeAnnotator responsible for generic type resolution. In a loop then incrementally patch these generic variables to their concrete type if the annotator has enough information to do so. Repeat until exhausted.

Note: Strictly speaking this is not type inference, rather its an extension of the generic type resolver but specific for variables for CFC's use-case. A much nicer implementation would have been type inference using something similar to the "Hindley–Milner type system" algorithm also used in e.g. rustc. Thats a bigger architectural change however.

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🐧 Linux

Artifact	Link	Size
deb-x86_64	Download	38.4 MB
schema	Download	0.0 MB
stdlib	Download	32.4 MB
plc-x86_64	Download	43.5 MB
deb-aarch64	Download	30.8 MB
plc-aarch64	Download	43.3 MB

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🪟 Windows

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stdlib.lib	Download	4.0 MB
stdlib.dll	Download	0.1 MB
plc.exe	Download	38.3 MB

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