source injector: add the crate

This crate takes an absolute path to a rustc repo and adds path-dependencies
that point towards the respective rustc subcrates into the Cargo.tomls of
the clippy and clippy_lints crate.

This allows rustc-analyzer to show proper type annotations etc on rustc-internals inside the clippy repo.

Usage: ./souce_injector/target/debug/souce_injector /absolute/path/to/rust/

cc rust-lang/rust-analyzer#3517
cc #5514

Author: matthiaskrgr

Diff for: .gitignore

@@ -21,6 +21,7 @@ out
 /clippy_workspace_tests/target
 /clippy_dev/target
 /rustc_tools_util/target
+/souce_injector/target
 
 # Generated by dogfood
 /target_recur/

Diff for: souce_injector/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "souce_injector"
+version = "0.1.0"
+authors = ["Matthias Krüger <matthias.krueger@famsik.de>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

Diff for: souce_injector/src/main.rs

@@ -0,0 +1,93 @@
+use std::env;
+use std::fs;
+use std::fs::File;
+use std::io::prelude::*;
+use std::path::PathBuf;
+
+// This crate takes an absolute path to a rustc repo and alters the dependencies to point towards
+// the respective rustc subcrates instead of using extern crate xyz.
+// This allows rust analyzer to analyze rustc internals and show proper information inside clippy
+// code. See  https://github.com/rust-lang/rust-clippy/issues/5514 and https://github.com/rust-lang/rust-clippy/issues/5514 for details
+
+fn main() -> std::io::Result<()> {
+    // first arg is the path to a rust repo
+    let rustc_path = env::args()
+        .nth(1)
+        .expect("First argument must be the path to a rustc repo root");
+
+    let rustc_path = PathBuf::from(rustc_path);
+    assert!(rustc_path.is_dir(), "path is not a directory");
+    let rustc_source_basedir = rustc_path.join("src");
+    assert!(
+        rustc_source_basedir.is_dir(),
+        "are you sure the path leads to a rustc repo?"
+    );
+
+    let clippy_root_manifest = fs::read_to_string("Cargo.toml").expect("failed to read ./Cargo.toml");
+    let clippy_root_lib_rs = fs::read_to_string("src/driver.rs").expect("failed to read ./src/driver.rs");
+    inject_deps_into_manifest(
+        &rustc_source_basedir,
+        "Cargo.toml",
+        clippy_root_manifest,
+        clippy_root_lib_rs,
+    )?;
+
+    let clippy_lints_manifest =
+        fs::read_to_string("clippy_lints/Cargo.toml").expect("failed to read ./clippy_lints/Cargo.toml");
+    let clippy_lints_lib_rs =
+        fs::read_to_string("clippy_lints/src/lib.rs").expect("failed to read ./clippy_lints/src/lib.rs");
+    inject_deps_into_manifest(
+        &rustc_source_basedir,
+        "clippy_lints/Cargo.toml",
+        clippy_lints_manifest,
+        clippy_lints_lib_rs,
+    )?;
+
+    Ok(())
+}
+
+fn inject_deps_into_manifest(
+    rustc_source_dir: &PathBuf,
+    manifest_path: &str,
+    cargo_toml: String,
+    lib_rs: String,
+) -> std::io::Result<()> {
+    let extern_crates = lib_rs
+        .lines()
+        // get the deps
+        .filter(|line| line.starts_with("extern crate"))
+        // we have something like "extern crate foo;", we only care about the "foo"
+        //              ↓          ↓
+        // extern crate rustc_middle;
+        .map(|s| &s[13..(s.len() - 1)]);
+
+    let new_deps = extern_crates.map(|dep| {
+        // format the dependencies that are going to be put inside the Cargo.toml
+        format!(
+            "{dep} = {{ path = \"{source_path}/lib{dep}\" }}\n",
+            dep = dep,
+            source_path = rustc_source_dir.display()
+        )
+    });
+
+    // format a new [dependencies]-block with the new deps we need to inject
+    let mut all_deps = String::from("[dependencies]\n");
+    new_deps.for_each(|dep_line| {
+        all_deps.push_str(&dep_line);
+    });
+
+    // replace "[dependencies]" with
+    // [dependencies]
+    // dep1 = { path = ... }
+    // dep2 = { path = ... }
+    // etc
+    let new_manifest = cargo_toml.replacen("[dependencies]\n", &all_deps, 1);
+
+    // println!("{}", new_manifest);
+    let mut file = File::create(manifest_path)?;
+    file.write_all(new_manifest.as_bytes())?;
+
+    println!("Dependency paths injected: {}", manifest_path);
+
+    Ok(())
+}