cargo dev ra-setup: don't inject deps multiple times if we have already done so

Fixes #6220

clippy_dev/src/ra_setup.rs

@@ -11,7 +11,7 @@ use std::path::PathBuf;
 // code. See https://github.com/rust-analyzer/rust-analyzer/issues/3517 and https://github.com/rust-lang/rust-clippy/issues/5514 for details
 
 pub fn run(rustc_path: Option<&str>) {
-    // we can unwrap here because the arg is required here
+    // we can unwrap here because the arg is required by clap
     let rustc_path = PathBuf::from(rustc_path.unwrap());
     assert!(rustc_path.is_dir(), "path is not a directory");
     let rustc_source_basedir = rustc_path.join("compiler");
@@ -49,6 +49,15 @@ fn inject_deps_into_manifest(
     cargo_toml: &str,
     lib_rs: &str,
 ) -> std::io::Result<()> {
+    // do not inject deps if we have aleady done so
+    if cargo_toml.contains("[target.'cfg(NOT_A_PLATFORM)'.dependencies]") {
+        eprintln!(
+            "cargo dev ra-setup: warning: deps already found inside {}, doing nothing.",
+            manifest_path
+        );
+        return Ok(());
+    }
+
     let extern_crates = lib_rs
         .lines()
         // get the deps