This removes use of the ExtractType trait from the deserialize_any function by changing the code to never call it. The ultimate goal is to remove use of specialization.

ExtractType and its use of specialization exists to allow deserialization of cli arguments. For each command, there is a struct with some members and serde's Deserialize trait is being derived. This is the argument struct for the mv command:

#[derive(Deserialize)]
pub struct MoveArgs {
    pub src: Tagged<PathBuf>,
    pub dst: Tagged<PathBuf>,
}

The cli arguments input by an user are being converted from a CallInfo struct to that command-specific struct using ConfigDeserializer. The only uses of the ExtractType trait in the codebase are in its Deserializer implementation where they help avoiding having to use serde beyond iterating over the fields of the command-specific structs: any field of a cli param is expected to be readable from a Tagged<Value>.

In order to reduce usage of ExtractType, this PR brings more data into format understandable by serde.

The command rg "\(Deserialize\)][^}]*\}" -U src/commands/* provides a list of command-param-structs that we have to handle. The field types can be extracted using rg "\(Deserialize\)][^}]*\}" -U src/commands/* | rg ": .*: " | sed 's/^.*: //' | sort | uniq:

bool,
Option<Tagged<PathBuf>>,
Option<Tagged<String>>,
Option<(Tagged<String>, Tagged<Value>)>,
Tagged<bool>,
Tagged<i64>,
Tagged<PathBuf>,
Tagged<String>,
value::Block,
Vec<Tagged<PathBuf>>,
Vec<Tagged<String>>,

Previously, all these types were parsed from Tagged<Value> instances using the ExtractType trait. Now, serde with its outside-to-inside model is being used to handle the logic to deserialize Vec<>, bool, Option<>, tuples, but we still defer to ExtractType when something is encountered that doesn't fit into the serde data model like Tagged or Block. Handling these via serde as well is still possible and subject of future PRs.

Useful commands for testing:

open tests/fixtures/formats/sample.bson | pick _id root // tests vec
config --set [specialization false] // tests Option containing a tuple

cc #362