hack: Try to preserve DSL v1 behaviour a bit more

This allows using `constructor` keyword in 0.4.22 but some
keywords are too eagerly reserved like `leave` in Yul since 0.6.0,
whereas it's actually reserved in 0.7.1.

See #568.

crates/solidity/inputs/language/src/definition.rs

@@ -193,26 +193,35 @@ fn resolve_token(
 }
 
 fn resolve_keyword(keyword: model::KeywordItem) -> codegen_grammar::ScannerDefinitionNode {
-    // FIXME: Handle reserved keywords using the given "Identifier" parser
-    let _identifier = keyword.identifier;
+    // TODO(#568): Handle reserved keywords using the given "Identifier" parser
+    let _ = keyword.identifier;
 
     let defs: Vec<_> = keyword
         .definitions
         .into_iter()
         .map(|def| {
-            // FIXME: Properly support contextual keywords.
-            // Currently, to minimize the diff and ease the transition to the DSL v2, we treat them as normal keywords.
-            // Moreover, since the DSL v1 only treats "enablement" as being reserved, we try to preserve that for now.
             let value = resolve_keyword_value(def.value);
             // If missing, the default is "Always"
             match (def.enabled, def.reserved) {
                 // Contextual keywords (never reserved)
+                // TODO(#568): Properly support contextual keywords.
+                // Currently, to minimize the diff and ease the transition to the DSL v2, we treat them as normal keywords.
+                // Moreover, since the DSL v1 only treats "enablement" as being reserved, we try to preserve that for now.
                 (enabled, Some(VersionSpecifier::Never)) => match enabled {
                     Some(enabled) => {
                         ScannerDefinitionNode::Versioned(Box::new(value), enabled_to_range(enabled))
                     }
                     None => value,
                 },
+                // TODO(#568): If a contextual keyword was enabled at some point and then reserved, for now we treat it
+                // as a reserved keyword starting from when it was being used, to preserve the DSL v1 behaviour.
+                (
+                    Some(VersionSpecifier::From { from: enabled }),
+                    Some(VersionSpecifier::From { from: reserved }),
+                ) if enabled < reserved => ScannerDefinitionNode::Versioned(
+                    Box::new(value),
+                    enabled_to_range(VersionSpecifier::From { from: enabled }),
+                ),
                 (_, Some(reserved)) => {
                     ScannerDefinitionNode::Versioned(Box::new(value), enabled_to_range(reserved))
                 }