internal: optimize compile time

cargo llvm-lines shows that path_to_error bloats the code. I don't think
I've needed this functionality recently, seems that we've fixed most of
the serialization problems. So let's just remove it. Should be easy to
add back if we ever need it, and it does make sense to keep the
`from_json` function around.

Cargo.lock

@@ -1315,7 +1315,6 @@ dependencies = [
  "rustc-hash",
  "serde",
  "serde_json",
- "serde_path_to_error",
  "sourcegen",
  "stdx",
  "syntax",
@@ -1453,15 +1452,6 @@ dependencies = [
  "serde",
 ]
 
-[[package]]
-name = "serde_path_to_error"
-version = "0.1.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "42f6109f0506e20f7e0f910e51a0079acf41da8e0694e6442527c4ddf5a2b158"
-dependencies = [
- "serde",
-]
-
 [[package]]
 name = "serde_repr"
 version = "0.1.7"

crates/rust-analyzer/Cargo.toml

@@ -31,7 +31,6 @@ oorandom = "11.1.2"
 rustc-hash = "1.1.0"
 serde = { version = "1.0.106", features = ["derive"] }
 serde_json = { version = "1.0.48", features = ["preserve_order"] }
-serde_path_to_error = "0.1"
 threadpool = "1.7.1"
 rayon = "1.5"
 mimalloc = { version = "0.1.19", default-features = false, optional = true }

crates/rust-analyzer/src/lib.rs

@@ -41,16 +41,17 @@ pub mod config;
 #[cfg(test)]
 mod integrated_benchmarks;
 
-use serde::de::DeserializeOwned;
 use std::fmt;
 
+use serde::de::DeserializeOwned;
+
 pub use crate::{caps::server_capabilities, main_loop::main_loop};
 
 pub type Error = Box<dyn std::error::Error + Send + Sync>;
 pub type Result<T, E = Error> = std::result::Result<T, E>;
 
 pub fn from_json<T: DeserializeOwned>(what: &'static str, json: serde_json::Value) -> Result<T> {
-    let res = serde_path_to_error::deserialize(&json)
+    let res = serde_json::from_value(json.clone())
         .map_err(|e| format!("Failed to deserialize {}: {}; {}", what, e, json))?;
     Ok(res)
 }