Issue 240507.1: Add support for "properties"

Martin Friebe

## Background

Pascal has a property construct, that allows a "variable like"
identifier, which can either point to a field (member variable) or a
getter/setter function.

    TFoo = class
      FField: integer;
      function GetProp: integer;
      procedure SetProp(AVal: Integer);
      property MyProp: integer read GetProp write SetProp;
      property MyOtherProp: integer read FField;
    end;

* Properties can exist in a structure, interface, or on a global level.

* Properties can be read/write, read only, write only.

* Properties can have one or more array like indexes (of any type).

        function GetProp(AIdx:word; AIdx2: boolean): integer;
        procedure SetProp(AIdx:word; AIdx2: boolean; AVal: Integer);
        property MyProp[AIdx:word; AIdx2: boolean]: integer read GetProp write SetProp;

* Properties can share a method, and provide an index (constant) to
  identify which property called the method.

        function GetProp(AIndex: Integer): integer;
        procedure SetProp(AIndex: Integer; AValue: integer);
        property MyProp1: integer index 1 read GetProp write SetProp;
        property MyProp2: integer index 2 read GetProp write SetProp;

* Properties can have a "default" flag, indicating that the array []
  access can omit the property name. I.e. accessing "Object[n]" is a
  shortcut for the default property. (default for non-array properties is
  being considered for future addition)

* Properties can have "default" and "stored" values for streaming
  (constant or via function).

* Properties can be elevated to a higher visibility (private/public) in
  inherited classes.

There may be partial overlaps with properties in Objective-C and C#.

Update: This proposal has been updated in a way to make to also useful
for properties in Objective-C and Swift.

### References

- [FreePascal property doc][freepascal]
- [Oxygene][oxygene]
- [Apple extension for Objective-C][objc]

[freepascal]: https://www.freepascal.org/docs-html/ref/refse27.html
[oxygene]: https://docs.elementscompiler.com/Oxygene/Members/Properties/
[objc]: https://github.com/llvm/llvm-project/blob/main/llvm/docs/SourceLevelDebugging.rst#debugging-information-format-1

## Proposed Changes

### Section 2.1: The Debugging Information Entry

In Table 2.1, add `DW_TAG_property`, `DW_TAG_property_getter`,
`DW_TAG_property_setter`, and `DW_TAG_property_stored`.

### New Section 5.7.11 Property Entries

A property member is represented by a debugging information entry with
the tag `DW_TAG_property` as specified in Section 5.19.

### New Section 5.19(?): Property Entries

Add the following new subsection to Chapter 5:

> 5.19(?) Property Entries
>
> [Non-normative] *Object-oriented languages like Pascal and
> Objective-C have properties, which are variable- or data member-like
> entities of units or classes. Syntactically, properties can be
> accessed like variables and data members, however, access is
> implemented by invoking user-defined or compiler-generated
> subprograms, allowing programmed constraints, including read-only
> and write-only semantics.*
>
> A property is represented by a debugging information entry with the

Author:	Martin Friebe
Champion:	Adrian Prantl
Date submitted:	2024-05-07
Date revised:	2025-04-16
Date closed:	2025-03-31
Type:	Enhancement
Status:	Accepted
DWARF version:	6