Language versions and feature gates

gdfmt_syntax::LanguageVersion, also re-exported by parser/config, provides five explicit grammar profiles: 4.3, 4.4, 4.5, 4.6, and 4.7. The default is fixed at 4.7. Profiles represent verified version differences in implemented syntax, not full engine conformance. The 4.8 preview, patch-version strings, latest, and unknown versions are rejected without silent fallback or network lookup.

use gdfmt_parser::{LanguageVersion, ParseOptions, parse};

let options = ParseOptions {
    language_version: LanguageVersion::Godot4_3,
    ..Default::default()
};
let result = parse("var data: Dictionary[String, int] = {}\n", &options);
assert!(result.diagnostics.iter().any(|d| d.code == "PAR017"));
assert_eq!(result.tree.unwrap().text(), "var data: Dictionary[String, int] = {}\n");

Configuration accepts "language": { "godotVersion": "4.5" }. Rust hosts pass config.language.godot_version to ParseOptions.language_version. Discovery, field merging, provenance, and JSON Schema use the same enum. CLI lex remains an independent lexical check.

Verified feature table

Feature	Earliest profile	Evidence
Dictionary[K, V] in declarations, return types, and as/is	4.4	4.4 release notes
@export_tool_button	4.4	4.4 beta 1 notes
@warning_ignore_start / @warning_ignore_restore	4.4	4.4 beta 1 notes
@abstract classes and methods	4.5	4.5 language reference
Rest parameters ...args, including static functions and lambdas	4.5	4.5 variadic functions
@export_file_path	4.5	Annotation registries in the 4.4 parser and 4.5 parser
Hint arguments for @export_multiline	4.6	Annotation registries in the 4.5 parser and 4.6 parser

Behavior and testing

LanguageFeature::since() defines the runtime feature table; LanguageVersion::supports() queries it. Earlier profiles report PAR017 while completing the lossless CST and other constraint checks. Invalid constructs still report their own PAR codes. Independent lex accepts no version parameter; recognizing a token does not establish version support.

Tests traverse every profile, covering positive/negative cases around the introduction version, scripts/expressions/lambdas, lossless recovery in older profiles, UTF-8 spans, and the shared diagnostic budget. When a manifest fixture specifies syntaxErrorsByVersion, it must cover every profile. cargo xtask compatibility checks the default profile and the complete matrix; missing or unknown profiles fail verification.

Type names, annotation argument values, inheritance/abstract overrides, runtime behavior, and complete 4.6/4.7 grammar differences require an analyzer and broader engine coverage. Stable 4.3, 4.4, 4.5, 4.6, and 4.7.2 are integrated with the pinned engine matrix; all seven gates have independent positive and negative cases. Namespace/trait remain unsupported.