Auto merge of #11045 - Alexendoo:extern-flags, r=flip1995

Use depinfo to discover UI test dependencies

changelog: none

context: https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Building.20test.20dependencies

This restores [the old `EXTERN_FLAGS` method](https://github.com/rust-lang/rust-clippy/blob/4cf5bdc60c7ccec3b5f395ee393615c224e28555/tests/compile-test.rs#L67-L75) of passing `--extern` flags for building UI tests with minor changes

- Unused deps were removed
- It's now a `Vec` of args instead of a command string
- It uses a `BTreeMap` so the extern flags are in alphabetical order and deterministic

I don't know if the `HOST_LIBS` part is still required, but I figured it best to leave it in for now. If the change is accepted we can take a look if it's needed in `rust-lang/rust` after the next sync

This isn't as pleasant as having a `Cargo.toml`, though there is something satisfying about knowing the dependencies are already built and not needing to invoke `cargo`

r? `@flip1995`

1 files changed, 109 insertions, 9 deletions

diff --git a/tests/compile-test.rs b/tests/compile-test.rs
index d37151b19b6..b86e6849d26 100644
--- a/tests/compile-test.rs
+++ b/tests/compile-test.rs
@@ -3,17 +3,108 @@
 #![feature(is_sorted)]
 #![cfg_attr(feature = "deny-warnings", deny(warnings))]
 #![warn(rust_2018_idioms, unused_lifetimes)]
+#![allow(unused_extern_crates)]
 
 use compiletest::{status_emitter, CommandBuilder};
 use ui_test as compiletest;
 use ui_test::Mode as TestMode;
 
+use std::collections::BTreeMap;
 use std::env::{self, remove_var, set_var, var_os};
 use std::ffi::{OsStr, OsString};
 use std::fs;
 use std::path::{Path, PathBuf};
+use std::sync::LazyLock;
 use test_utils::IS_RUSTC_TEST_SUITE;
 
+// Test dependencies may need an `extern crate` here to ensure that they show up
+// in the depinfo file (otherwise cargo thinks they are unused)
+extern crate clippy_lints;
+extern crate clippy_utils;
+extern crate derive_new;
+extern crate futures;
+extern crate if_chain;
+extern crate itertools;
+extern crate parking_lot;
+extern crate quote;
+extern crate syn;
+extern crate tokio;
+
+/// All crates used in UI tests are listed here
+static TEST_DEPENDENCIES: &[&str] = &[
+    "clippy_lints",
+    "clippy_utils",
+    "derive_new",
+    "futures",
+    "if_chain",
+    "itertools",
+    "parking_lot",
+    "quote",
+    "regex",
+    "serde_derive",
+    "serde",
+    "syn",
+    "tokio",
+];
+
+/// Produces a string with an `--extern` flag for all UI test crate
+/// dependencies.
+///
+/// The dependency files are located by parsing the depinfo file for this test
+/// module. This assumes the `-Z binary-dep-depinfo` flag is enabled. All test
+/// dependencies must be added to Cargo.toml at the project root. Test
+/// dependencies that are not *directly* used by this test module require an
+/// `extern crate` declaration.
+static EXTERN_FLAGS: LazyLock<Vec<String>> = LazyLock::new(|| {
+    let current_exe_depinfo = {
+        let mut path = env::current_exe().unwrap();
+        path.set_extension("d");
+        fs::read_to_string(path).unwrap()
+    };
+    let mut crates = BTreeMap::<&str, &str>::new();
+    for line in current_exe_depinfo.lines() {
+        // each dependency is expected to have a Makefile rule like `/path/to/crate-hash.rlib:`
+        let parse_name_path = || {
+            if line.starts_with(char::is_whitespace) {
+                return None;
+            }
+            let path_str = line.strip_suffix(':')?;
+            let path = Path::new(path_str);
+            if !matches!(path.extension()?.to_str()?, "rlib" | "so" | "dylib" | "dll") {
+                return None;
+            }
+            let (name, _hash) = path.file_stem()?.to_str()?.rsplit_once('-')?;
+            // the "lib" prefix is not present for dll files
+            let name = name.strip_prefix("lib").unwrap_or(name);
+            Some((name, path_str))
+        };
+        if let Some((name, path)) = parse_name_path() {
+            if TEST_DEPENDENCIES.contains(&name) {
+                // A dependency may be listed twice if it is available in sysroot,
+                // and the sysroot dependencies are listed first. As of the writing,
+                // this only seems to apply to if_chain.
+                crates.insert(name, path);
+            }
+        }
+    }
+    let not_found: Vec<&str> = TEST_DEPENDENCIES
+        .iter()
+        .copied()
+        .filter(|n| !crates.contains_key(n))
+        .collect();
+    assert!(
+        not_found.is_empty(),
+        "dependencies not found in depinfo: {not_found:?}\n\
+        help: Make sure the `-Z binary-dep-depinfo` rust flag is enabled\n\
+        help: Try adding to dev-dependencies in Cargo.toml\n\
+        help: Be sure to also add `extern crate ...;` to tests/compile-test.rs",
+    );
+    crates
+        .into_iter()
+        .map(|(name, path)| format!("--extern={name}={path}"))
+        .collect()
+});
+
 mod test_utils;
 
 // whether to run internal tests or not
@@ -29,7 +120,6 @@ fn base_config(test_dir: &str) -> compiletest::Config {
         } else {
             compiletest::OutputConflictHandling::Error("cargo test -- -- --bless".into())
         },
-        dependencies_crate_manifest_path: Some("clippy_test_deps/Cargo.toml".into()),
         target: None,
         out_dir: "target/ui_test".into(),
         ..compiletest::Config::rustc(Path::new("tests").join(test_dir))
@@ -44,10 +134,23 @@ fn base_config(test_dir: &str) -> compiletest::Config {
     let deps_path = current_exe_path.parent().unwrap();
     let profile_path = deps_path.parent().unwrap();
 
-    config.program.args.push("--emit=metadata".into());
-    config.program.args.push("-Aunused".into());
-    config.program.args.push("-Zui-testing".into());
-    config.program.args.push("-Dwarnings".into());
+    config.program.args.extend(
+        [
+            "--emit=metadata",
+            "-Aunused",
+            "-Zui-testing",
+            "-Dwarnings",
+            &format!("-Ldependency={}", deps_path.display()),
+        ]
+        .map(OsString::from),
+    );
+
+    config.program.args.extend(EXTERN_FLAGS.iter().map(OsString::from));
+
+    if let Some(host_libs) = option_env!("HOST_LIBS") {
+        let dep = format!("-Ldependency={}", Path::new(host_libs).join("deps").display());
+        config.program.args.push(dep.into());
+    }
 
     // Normalize away slashes in windows paths.
     config.stderr_filter(r"\\", "/");
@@ -105,9 +208,7 @@ fn run_internal_tests() {
     if !RUN_INTERNAL_TESTS {
         return;
     }
-    let mut config = base_config("ui-internal");
-    config.dependency_builder.args.push("--features".into());
-    config.dependency_builder.args.push("internal".into());
+    let config = base_config("ui-internal");
     compiletest::run_tests(config).unwrap();
 }
 
@@ -165,7 +266,6 @@ fn run_ui_cargo() {
         .push(("RUSTFLAGS".into(), Some("-Dwarnings".into())));
     // We need to do this while we still have a rustc in the `program` field.
     config.fill_host_and_target().unwrap();
-    config.dependencies_crate_manifest_path = None;
     config.program.program.set_file_name(if cfg!(windows) {
         "cargo-clippy.exe"
     } else {