This commit add Cargo-style project discovery for Buck and Bazel users.

This feature requires the user to add a command that generates a
`rust-project.json` from a set of files. Project discovery can be invoked
in two ways:

1. At extension activation time, which includes the generated
   `rust-project.json` as part of the linkedProjects argument in
    InitializeParams
2. Through a new command titled "Add current file to workspace", which
   makes use of a new, rust-analyzer specific LSP request that adds
   the workspace without erasing any existing workspaces.

I think that the command-running functionality _could_ merit being
placed into its own extension (and expose it via extension contribution
points), if only provide build-system idiomatic progress reporting and
status handling, but I haven't (yet) made an extension that does this.

crates/project-model/src/cfg_flag.rs

@@ -4,6 +4,7 @@
 use std::{fmt, str::FromStr};
 
 use cfg::CfgOptions;
+use serde::Serialize;
 
 #[derive(Clone, Eq, PartialEq, Debug)]
 pub enum CfgFlag {
@@ -38,6 +39,18 @@ impl<'de> serde::Deserialize<'de> for CfgFlag {
     }
 }
 
+impl Serialize for CfgFlag {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        match self {
+            CfgFlag::Atom(s) => serializer.serialize_str(s),
+            CfgFlag::KeyValue { .. } => serializer.serialize_str(&format!("{}", &self)),
+        }
+    }
+}
+
 impl Extend<CfgFlag> for CfgOptions {
     fn extend<T: IntoIterator<Item = CfgFlag>>(&mut self, iter: T) {
         for cfg_flag in iter {

crates/project-model/src/project_json.rs

@@ -54,7 +54,7 @@ use std::path::PathBuf;
 use base_db::{CrateDisplayName, CrateId, CrateName, Dependency, Edition};
 use paths::{AbsPath, AbsPathBuf};
 use rustc_hash::FxHashMap;
-use serde::{de, Deserialize};
+use serde::{de, ser, Deserialize, Serialize};
 
 use crate::cfg_flag::CfgFlag;
 
@@ -171,14 +171,14 @@ impl ProjectJson {
     }
 }
 
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 pub struct ProjectJsonData {
     sysroot: Option<PathBuf>,
     sysroot_src: Option<PathBuf>,
     crates: Vec<CrateData>,
 }
 
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 struct CrateData {
     display_name: Option<String>,
     root_module: PathBuf,
@@ -200,7 +200,7 @@ struct CrateData {
     repository: Option<String>,
 }
 
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 #[serde(rename = "edition")]
 enum EditionData {
     #[serde(rename = "2015")]
@@ -221,16 +221,16 @@ impl From<EditionData> for Edition {
     }
 }
 
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 struct DepData {
     /// Identifies a crate by position in the crates array.
     #[serde(rename = "crate")]
     krate: usize,
-    #[serde(deserialize_with = "deserialize_crate_name")]
+    #[serde(deserialize_with = "deserialize_crate_name", serialize_with = "serialize_crate_name")]
     name: CrateName,
 }
 
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 struct CrateSource {
     include_dirs: Vec<PathBuf>,
     exclude_dirs: Vec<PathBuf>,
@@ -243,3 +243,10 @@ where
     let name = String::deserialize(de)?;
     CrateName::new(&name).map_err(|err| de::Error::custom(format!("invalid crate name: {err:?}")))
 }
+
+fn serialize_crate_name<S>(crate_name: &CrateName, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: ser::Serializer,
+{
+    crate_name.serialize(serializer)
+}