syntax_data: {"ast_node_type":"other","tokens":[{"end":35,"kind":"keyword","start":0,"text":"BuiltinImpl(BuiltinImplSource),"}]}
source_snippet:     BuiltinImpl(BuiltinImplSource),
context_before:     /// `EvalCtxt::assemble_builtin_impl_candidates` method.
context_after:     /// An assumption from the environment. Stores a [`ParamEnvSource`], since we