save-analysis: Use serde instead of libserialize to dump JSON data

Cargo.lock

@@ -2933,11 +2933,11 @@ dependencies = [
  "rls-data 0.18.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rls-span 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
- "rustc-serialize 0.3.24 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_codegen_utils 0.0.0",
  "rustc_data_structures 0.0.0",
  "rustc_target 0.0.0",
  "rustc_typeck 0.0.0",
+ "serde_json 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
 ]

src/librustc_save_analysis/Cargo.toml

@@ -16,9 +16,8 @@ rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_codegen_utils = { path = "../librustc_codegen_utils" }
 rustc_target = { path = "../librustc_target" }
 rustc_typeck = { path = "../librustc_typeck" }
+serde_json = "1"
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
 rls-data = "0.18.1"
 rls-span = "0.4"
-# FIXME(#40527) should move rustc serialize out of tree
-rustc-serialize = "0.3"

src/librustc_save_analysis/json_dumper.rs

 use std::io::Write;
 
-use rustc_serialize::json::as_json;
-
 use rls_data::config::Config;
 use rls_data::{self, Analysis, CompilationOptions, CratePreludeData, Def, DefKind, Impl, Import,
                MacroRef, Ref, RefKind, Relation};
@@ -31,8 +29,8 @@ pub struct WriteOutput<'b, W: Write> {
 
 impl<'b, W: Write> DumpOutput for WriteOutput<'b, W> {
     fn dump(&mut self, result: &Analysis) {
-        if write!(self.output, "{}", as_json(&result)).is_err() {
-            error!("Error writing output");
+        if let Err(e) = serde_json::to_writer(self.output.by_ref(), result) {
+            error!("Can't serialize save-analysis: {:?}", e);
         }
     }
 }

src/librustc_save_analysis/lib.rs

@@ -1141,10 +1141,15 @@ fn find_config(supplied: Option<Config>) -> Config {
     if let Some(config) = supplied {
         return config;
     }
+
     match env::var_os("RUST_SAVE_ANALYSIS_CONFIG") {
-        Some(config_string) => rustc_serialize::json::decode(config_string.to_str().unwrap())
-            .expect("Could not deserialize save-analysis config"),
         None => Config::default(),
+        Some(config) => config.to_str()
+            .ok_or(())
+            .map_err(|_| error!("`RUST_SAVE_ANALYSIS_CONFIG` isn't UTF-8"))
+            .and_then(|cfg|  serde_json::from_str(cfg)
+                .map_err(|_| error!("Could not deserialize save-analysis config"))
+            ).unwrap_or_default()
     }
 }