rdl: replace class body interface list with colon-list syntax

[Copilot]

The windows-rdl class syntax listed implemented interfaces inside the class body with an explicit #[default] attribute marker. This changes the syntax to a cleaner colon-separated inheritance list where position implies default, freeing the body for future use.

Old syntax:

class Derived: Base {
    #[default]
    IDerived,
    IDerived2,
}

New syntax:

class Derived: Base, IDerived, IDerived2 {}

The first interface in the colon list is implicitly the default — no attribute needed. The base class (if any) must appear before interfaces and is distinguished at encode time by checking whether the resolved type is a class or interface.

Reader (src/reader/class.rs)

• Removed ClassInterface struct; Class now holds colon_list: Vec<syn::Path>
• Parser accepts class Name: Path1, Path2 {} — body is parsed but must be empty
• Encoder resolves each path via encode_path(), uses new is_class_type() helper (checks local Index for Item::Class, reference for TypeCategory::Class) to route each entry to either extends or InterfaceImpl; first interface automatically receives DefaultAttribute
• Validates: at most one base class, base must precede interfaces, body must be empty

Writer (src/writer/class.rs)

• Sorts interface_impls() so the default interface leads, then emits a single colon list with an empty {} body

Formatter (src/formatter/mod.rs)

• Added in_colon_list flag that is set when a : token is encountered inside a mod/namespace body and outside parentheses/angle-brackets, cleared on { or ;
• While in_colon_list is active, commas emit a space instead of a newline, keeping the entire inheritance list on one line (e.g. class Derived: Base, IDerived, IDerived2 {})
• Added body_stack: Vec<bool> and last_keyword_is_mod flag to correctly classify open braces: only mod introduces a namespace body (false) where : is an inheritance separator; all other bodies — struct, union, attribute, fn, class, interface, and anonymous inline types — are classified as field bodies (true) where : is a field-name-to-type separator and must not trigger in_colon_list

Samples (crates/samples/components/json_validator_winrt/src/sample.rdl)

• Updated sample.rdl to use the new colon-list class syntax (class JsonValidator: IJsonValidator {})

Tests & docs

• tests/class.rdl updated to new syntax
• rdl.md updated with new grammar description and example

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[kennykerr]

@copilot the line breaks here are weird. I think it should be Base, IDerived, IDerived2 all on one line.

[Copilot]

Fixed in a25cdff. The root cause was the formatter's Token::Comma handler always emitting a newline when outside parentheses/angles. I added an in_colon_list flag to the formatter that gets set when a : is encountered outside parens/angles and cleared on { or ;, so commas in the class header now emit a space instead of a newline. class Derived: Base, IDerived, IDerived2 {} is now all on one line.

[kennykerr]

@copilot this looks like a formatting regression.

[Copilot]

Fixed in cbcb3f9. The previous in_colon_list fix was too broad — it also triggered on struct field colons (base: Type), causing fields to be formatted on a single line. I added a body_stack: Vec<bool> to the formatter that records whether each { opens a struct/enum body (true) or a mod/namespace body (false). in_colon_list is now only set when the : is outside parentheses/angles and the current body is not a struct/enum body. Struct fields are back on separate lines while class header inheritance lists remain on one line.

[kennykerr]

@copilot more formatting regressions - may want to consider simplifying the formatter...

[Copilot]

Fixed in 4ce659e. The root cause was the same as the previous regression but more pervasive: union, attribute, class, and interface are all Identifier tokens in the lexer (not keywords), so any body opened after them was incorrectly classified as a namespace/mod body, causing field colons to trigger in_colon_list.

Simplified the approach: instead of trying to track all "struct-like" keywords, I now only track last_keyword_is_mod. Only mod introduces a namespace body where : is an inheritance separator — all other bodies suppress in_colon_list. The body_stack stores false for mod bodies and true for everything else, and in_colon_list is only set when body_stack.last() == Some(&false).

This is both simpler and correct for all body types including union, attribute, anonymous inline struct/union fields, and nested unions.

[kennykerr]

@copilot fix the build

[Copilot]

@copilot fix the build

Fixed in 78675de. The crates/samples/components/json_validator_winrt/src/sample.rdl sample was still using the old class body syntax. Updated to the new colon-list syntax: class JsonValidator: IJsonValidator {}