You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: encoder.rs
    path of file: ./repos/creusot/creusot-metadata/src
    
    the code of the file until where you have to start completion: use crate::{
    AbsoluteBytePos, EncodedSourceFileId, Footer, SourceFileIndex, SYMBOL_OFFSET,
    SYMBOL_PREINTERNED, SYMBOL_STR, TAG_FULL_SPAN, TAG_PARTIAL_SPAN,
};
use rustc_data_structures::{fx::FxHashMap, sync::Lrc};
use rustc_hir::def_id::{CrateNum, DefId, DefIndex};
use rustc_middle::{
    dep_graph::DepContext,
    ty::{self, codec::TyEncoder, PredicateKind, Ty, TyCtxt},
};
use rustc_serialize::{
    opaque::{FileEncoder, IntEncodedWithFixedSize},
    Encodable, Encoder,
};
use rustc_span::{
    hygiene::{raw_encode_syntax_context, HygieneEncodeContext},
    ExpnId, SourceFile, Span, Symbol, SyntaxCon
    
    fn encode(&self, s: &mut MetadataEncoder<'a, 'tcx>) {
        // if symbol preinterned, emit tag and symbol index
        if self.is_preinterned() {
            s.opaque.emit_u8(SYMBOL_PREINTERNED);
            s.opaque.emit_u32(self.as_u32());
        } else {
            // otherwise write it as string or as offset to it
            match s.symbol_table.entry(*self) {
                Entry::Vacant(o) => {
                    s.opaque.emit_u8(SYMBOL_STR);
                    let pos = s.opaque.position();
                    o.insert(pos);
                    s.emit_str(self.as_str());
                }
                Entry::Occupied(o) => {
                    let x = *o.get();
                    s.emit_u8(SYMBOL_OFFSET);
                    s.emit_usize(x);
                }
            }
        }
    }