Let Cargo track `CLIPPY_ARGS`

3 files changed, 117 insertions, 41 deletions

diff --git a/README.md b/README.md
index 3cc03cf3603..63057609bb6 100644
--- a/README.md
+++ b/README.md
@@ -202,7 +202,6 @@ the lint(s) you are interested in:
 ```terminal
 cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::...
 ```
-Note that if you've run clippy before, this may only take effect after you've modified a file or ran `cargo clean`.
 
 ### Specifying the minimum supported Rust version
 
diff --git a/src/driver.rs b/src/driver.rs
index d5143e1438e..081a2ddeb16 100644
--- a/src/driver.rs
+++ b/src/driver.rs
@@ -11,12 +11,16 @@
 extern crate rustc_driver;
 extern crate rustc_errors;
 extern crate rustc_interface;
+extern crate rustc_session;
+extern crate rustc_span;
 
 use rustc_interface::interface;
+use rustc_session::Session;
+use rustc_span::symbol::Symbol;
 use rustc_tools_util::VersionInfo;
 
 use std::borrow::Cow;
-use std::env;
+use std::env::{self, VarError};
 use std::lazy::SyncLazy;
 use std::ops::Deref;
 use std::panic;
@@ -59,13 +63,42 @@ fn test_arg_value() {
     assert_eq!(arg_value(args, "--foo", |_| true), None);
 }
 
+fn track_clippy_args(sess: &Session, args_env_var: &Option<String>) {
+    sess.parse_sess.env_depinfo.borrow_mut().insert((
+        Symbol::intern("CLIPPY_ARGS"),
+        args_env_var.as_deref().map(Symbol::intern),
+    ));
+}
+
 struct DefaultCallbacks;
 impl rustc_driver::Callbacks for DefaultCallbacks {}
 
-struct ClippyCallbacks;
+struct ClippyArgsCallbacks {
+    clippy_args_var: Option<String>,
+}
+
+impl rustc_driver::Callbacks for ClippyArgsCallbacks {
+    fn config(&mut self, config: &mut interface::Config) {
+        let previous = config.register_lints.take();
+        let clippy_args_var = self.clippy_args_var.take();
+        config.register_lints = Some(Box::new(move |sess, lint_store| {
+            if let Some(ref previous) = previous {
+                (previous)(sess, lint_store);
+            }
+
+            track_clippy_args(sess, &clippy_args_var);
+        }));
+    }
+}
+
+struct ClippyCallbacks {
+    clippy_args_var: Option<String>,
+}
+
 impl rustc_driver::Callbacks for ClippyCallbacks {
     fn config(&mut self, config: &mut interface::Config) {
         let previous = config.register_lints.take();
+        let clippy_args_var = self.clippy_args_var.take();
         config.register_lints = Some(Box::new(move |sess, mut lint_store| {
             // technically we're ~guaranteed that this is none but might as well call anything that
             // is there already. Certainly it can't hurt.
@@ -73,6 +106,8 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
                 (previous)(sess, lint_store);
             }
 
+            track_clippy_args(sess, &clippy_args_var);
+
             let conf = clippy_lints::read_conf(&[], &sess);
             clippy_lints::register_plugins(&mut lint_store, &sess, &conf);
             clippy_lints::register_pre_expansion_lints(&mut lint_store);
@@ -277,7 +312,15 @@ pub fn main() {
         };
 
         let mut no_deps = false;
-        let clippy_args = env::var("CLIPPY_ARGS")
+        let clippy_args_var = env::var("CLIPPY_ARGS").map_or_else(
+            |e| match e {
+                VarError::NotPresent => None,
+                VarError::NotUnicode(s) => panic!("CLIPPY_ARGS is not valid Unicode: {:?}", s),
+            },
+            Some,
+        );
+        let clippy_args = clippy_args_var
+            .as_deref()
             .unwrap_or_default()
             .split("__CLIPPY_HACKERY__")
             .filter_map(|s| match s {
@@ -305,11 +348,10 @@ pub fn main() {
             args.extend(clippy_args);
         }
 
-        let mut clippy = ClippyCallbacks;
-        let mut default = DefaultCallbacks;
-        let callbacks: &mut (dyn rustc_driver::Callbacks + Send) =
-            if clippy_enabled { &mut clippy } else { &mut default };
-
-        rustc_driver::RunCompiler::new(&args, callbacks).run()
+        if clippy_enabled {
+            rustc_driver::RunCompiler::new(&args, &mut ClippyCallbacks { clippy_args_var }).run()
+        } else {
+            rustc_driver::RunCompiler::new(&args, &mut ClippyArgsCallbacks { clippy_args_var }).run()
+        }
     }))
 }
diff --git a/tests/dogfood.rs b/tests/dogfood.rs
index 8fe48a67beb..2505836a5ed 100644
--- a/tests/dogfood.rs
+++ b/tests/dogfood.rs
@@ -3,7 +3,7 @@
 #![feature(once_cell)]
 
 use std::lazy::SyncLazy;
-use std::path::{Path, PathBuf};
+use std::path::PathBuf;
 use std::process::Command;
 
 mod cargo;
@@ -49,17 +49,6 @@ fn dogfood_clippy() {
 #[test]
 fn dogfood_subprojects() {
     fn test_no_deps_ignores_path_deps_in_workspaces() {
-        fn clean(cwd: &Path, target_dir: &Path) {
-            Command::new("cargo")
-                .current_dir(cwd)
-                .env("CARGO_TARGET_DIR", target_dir)
-                .arg("clean")
-                .args(&["-p", "subcrate"])
-                .args(&["-p", "path_dep"])
-                .output()
-                .unwrap();
-        }
-
         if cargo::is_rustc_test_suite() {
             return;
         }
@@ -68,7 +57,14 @@ fn dogfood_subprojects() {
         let cwd = root.join("clippy_workspace_tests");
 
         // Make sure we start with a clean state
-        clean(&cwd, &target_dir);
+        Command::new("cargo")
+            .current_dir(&cwd)
+            .env("CARGO_TARGET_DIR", &target_dir)
+            .arg("clean")
+            .args(&["-p", "subcrate"])
+            .args(&["-p", "path_dep"])
+            .output()
+            .unwrap();
 
         // `path_dep` is a path dependency of `subcrate` that would trigger a denied lint.
         // Make sure that with the `--no-deps` argument Clippy does not run on `path_dep`.
@@ -90,26 +86,65 @@ fn dogfood_subprojects() {
 
         assert!(output.status.success());
 
-        // Make sure we start with a clean state
-        clean(&cwd, &target_dir);
+        let lint_path_dep = || {
+            // Test that without the `--no-deps` argument, `path_dep` is linted.
+            let output = Command::new(&*CLIPPY_PATH)
+                .current_dir(&cwd)
+                .env("CLIPPY_DOGFOOD", "1")
+                .env("CARGO_INCREMENTAL", "0")
+                .arg("clippy")
+                .args(&["-p", "subcrate"])
+                .arg("--")
+                .arg("-Cdebuginfo=0") // disable debuginfo to generate less data in the target dir
+                .args(&["--cfg", r#"feature="primary_package_test""#])
+                .output()
+                .unwrap();
+            println!("status: {}", output.status);
+            println!("stdout: {}", String::from_utf8_lossy(&output.stdout));
+            println!("stderr: {}", String::from_utf8_lossy(&output.stderr));
+
+            assert!(!output.status.success());
+            assert!(
+                String::from_utf8(output.stderr)
+                    .unwrap()
+                    .contains("error: empty `loop {}` wastes CPU cycles")
+            );
+        };
+
+        // Make sure Cargo is aware of the removal of `--no-deps`.
+        lint_path_dep();
+
+        let successful_build = || {
+            let output = Command::new(&*CLIPPY_PATH)
+                .current_dir(&cwd)
+                .env("CLIPPY_DOGFOOD", "1")
+                .env("CARGO_INCREMENTAL", "0")
+                .arg("clippy")
+                .args(&["-p", "subcrate"])
+                .arg("--")
+                .arg("-Cdebuginfo=0") // disable debuginfo to generate less data in the target dir
+                .output()
+                .unwrap();
+            println!("status: {}", output.status);
+            println!("stdout: {}", String::from_utf8_lossy(&output.stdout));
+            println!("stderr: {}", String::from_utf8_lossy(&output.stderr));
 
-        // Test that without the `--no-deps` argument, `path_dep` is linted.
-        let output = Command::new(&*CLIPPY_PATH)
-            .current_dir(&cwd)
-            .env("CLIPPY_DOGFOOD", "1")
-            .env("CARGO_INCREMENTAL", "0")
-            .arg("clippy")
-            .args(&["-p", "subcrate"])
-            .arg("--")
-            .arg("-Cdebuginfo=0") // disable debuginfo to generate less data in the target dir
-            .args(&["--cfg", r#"feature="primary_package_test""#])
-            .output()
-            .unwrap();
-        println!("status: {}", output.status);
-        println!("stdout: {}", String::from_utf8_lossy(&output.stdout));
-        println!("stderr: {}", String::from_utf8_lossy(&output.stderr));
+            assert!(output.status.success());
+
+            output
+        };
+
+        // Trigger a sucessful build, so Cargo would like to cache the build result.
+        successful_build();
+
+        // Make sure there's no spurious rebuild when nothing changes.
+        let stderr = String::from_utf8(successful_build().stderr).unwrap();
+        assert!(!stderr.contains("Compiling"));
+        assert!(!stderr.contains("Checking"));
+        assert!(stderr.contains("Finished"));
 
-        assert!(!output.status.success());
+        // Make sure Cargo is aware of the new `--cfg` flag.
+        lint_path_dep();
     }
 
     // run clippy on remaining subprojects and fail the test if lint warnings are reported