lifetimes.rs

    pub fn get_pattern_source(&self, pat: &Pat) -> Option<PatternSource<'hir>> {
        let id = // get id 
        match self.find(id) {
            Some(NodeExpr(ref e)) => {
                Some(PatternSource::MatchExpr(e))
            }
            Some(NodeStmt(ref s)) => {
                match s.node {
                    StmtDecl(ref decl, _) => {
                        match decl.clone().unwrap().node {
                            DeclLocal(ref local) => Some(PatternSource::LetDecl(local)),
                            _ => {
                                return None;
                            },
                        }
                    }
                    _ => {
                        return None;
                    },
               }
            }
            _ => {
                return None;
            }
        }
    }