error: failed to select a version for `syn` - rust

Question

error: failed to select a version for `syn`. \
... required by package `serde_derive v1.0.125`\
... which satisfies dependency `serde_derive = "=1.0.125"` of package `serde v1.0.125`
... which satisfies dependency `serde = "^1.0.125"` of package `mongodb v2.1.0`\
... which satisfies dependency `mongodb = "^2.1"` of package `wagmeet v0.1.0
\(/mnt/e/College/Eighth Semester/Crypto_Capable/wagmeet_app)`\
versions that meet the requirements `^1.0.60` are: 1.0.86, 1.0.85, 1.0.84, 1.0.83, 1.0.82, 1.0.81, 1.0.80, 1.0.79, 1.0.78, 1.0.77, 1.0.76, 1.0.75, 1.0.74, 1.0.73, 1.0.72, 1.0.71, 1.0.70, 1.0.69, 1.0.68, 1.0.67, 1.0.66, 1.0.65, 1.0.64, 1.0.63, 1.0.62, 1.0.61, 1.0.60
all possible versions conflict with previously selected packages.
previously selected package `syn v1.0.57`\
... which satisfies dependency `syn = "=1.0.57"`
\ of package `near-sdk-core v3.0.1`
... which satisfies dependency `near-sdk-core = "=3.0.1"` of package `near-sdk-macros v3.0.1` \
... which satisfies dependency `near-sdk-macros = "=3.0.1"` \ of package `near-sdk v3.0.1`
... which satisfies dependency `near-sdk = "^3"` of package `wagmeet v0.1.0 `\
failed to select a version for `syn` which could resolve this conflict
Cargo.toml file
[package]
name = "wagmeet"
version = "0.1.0"
edition = "2021"
[lib]
crate-type = ["rlib","cdylib"]
[dependencies]
near-sdk = "^3.1.0"
near-contract-standards = "^3.1.1"
mongodb = "2.0.0"
bson = { version = "2", features = ["chrono-0_4"] } # Needed for using chrono datetime in doc
tokio = "1"
chrono = "0.4" # Used for setting DateTimes
serde = "1"
serde_derive = "1.0.135"
Update
added the cargo.toml file
I have tried various versions nothing seems to be working for now. Is mongoDb even compatible with Near protocol?

Answer 1

There is a conflict between two of your dependencies: near-sdk requires exactly syn version 1.0.57, and mongodb requires at least syn version 1.0.60. Clearly both cannot exist together.
You have few solutions:
Patch near-sdk to support later syn versions. This is usually not recommended.
Upgrade near-sdk to the pre-release 4.0.0 (currently 4.0.0-pre.7) that supports later syn versions. This is an unstable version, and may break.
Downgrade mongodb to a version that supports syn version 1.0.57. The latest version that supports that is 1.2.5, so you need to specify in your Cargo.toml mongodb = "=1.2.5". But this relies on an old, unsupported version.
There is no "best solution". All solutions are bad. I would probably upgrade near-sdk to 4.0.0, but what to do depends on your needs.

Answer 2

Try the following methods...
check your patched dependencies are pointed to the correct source repository
if you use other project's Cargo.lock or change some dependencies as you go, remove target folder and build again
check compilation logs for incorrect dependency paths!
update your Rust
delete .cargo and .rustup directories