tidy: check_crate_duplicate is no longer useful

After cargo becomes a workspace, no one uses `check_crate_duplicate` to
check if cargo is a dependency anymore.

Author: weihanglo

src/tools/tidy/src/deps.rs

@@ -335,13 +335,6 @@ const PERMITTED_CRANELIFT_DEPENDENCIES: &[&str] = &[
     "windows_x86_64_msvc",
 ];
 
-const FORBIDDEN_TO_HAVE_DUPLICATES: &[&str] = &[
-    // This crate takes quite a long time to build, so don't allow two versions of them
-    // to accidentally sneak into our dependency graph, in order to ensure we keep our CI times
-    // under control.
-    "cargo",
-];
-
 /// Dependency checks.
 ///
 /// `root` is path to the directory with the root `Cargo.toml` (for the workspace). `cargo` is path
@@ -361,7 +354,6 @@ pub fn check(root: &Path, cargo: &Path, bad: &mut bool) {
         &["rustc_driver", "rustc_codegen_llvm"],
         bad,
     );
-    check_crate_duplicate(&metadata, &[], bad);
 
     // Check cargo independently as it has it's own workspace.
     let mut cmd = cargo_metadata::MetadataCommand::new();
@@ -371,7 +363,6 @@ pub fn check(root: &Path, cargo: &Path, bad: &mut bool) {
     let cargo_metadata = t!(cmd.exec());
     let runtime_ids = HashSet::new();
     check_license_exceptions(&cargo_metadata, EXCEPTIONS_CARGO, runtime_ids, bad);
-    check_crate_duplicate(&cargo_metadata, FORBIDDEN_TO_HAVE_DUPLICATES, bad);
     check_rustfix(&metadata, &cargo_metadata, bad);
 
     // Check rustc_codegen_cranelift independently as it has it's own workspace.
@@ -389,7 +380,6 @@ pub fn check(root: &Path, cargo: &Path, bad: &mut bool) {
         &["rustc_codegen_cranelift"],
         bad,
     );
-    check_crate_duplicate(&metadata, &[], bad);
 
     let mut cmd = cargo_metadata::MetadataCommand::new();
     cmd.cargo_path(cargo)
@@ -535,40 +525,6 @@ fn check_permitted_dependencies(
     }
 }
 
-/// Prevents multiple versions of some expensive crates.
-fn check_crate_duplicate(
-    metadata: &Metadata,
-    forbidden_to_have_duplicates: &[&str],
-    bad: &mut bool,
-) {
-    for &name in forbidden_to_have_duplicates {
-        let matches: Vec<_> = metadata.packages.iter().filter(|pkg| pkg.name == name).collect();
-        match matches.len() {
-            0 => {
-                tidy_error!(
-                    bad,
-                    "crate `{}` is missing, update `check_crate_duplicate` \
-                    if it is no longer used",
-                    name
-                );
-            }
-            1 => {}
-            _ => {
-                tidy_error!(
-                    bad,
-                    "crate `{}` is duplicated in `Cargo.lock`, \
-                    it is too expensive to build multiple times, \
-                    so make sure only one version appears across all dependencies",
-                    name
-                );
-                for pkg in matches {
-                    println!("  * {}", pkg.id);
-                }
-            }
-        }
-    }
-}
-
 /// Finds a package with the given name.
 fn pkg_from_name<'a>(metadata: &'a Metadata, name: &'static str) -> &'a Package {
     let mut i = metadata.packages.iter().filter(|p| p.name == name);
@@ -618,18 +574,23 @@ fn deps_of_filtered<'a>(
     }
 }
 
-fn direct_deps_of<'a>(metadata: &'a Metadata, pkg_id: &'a PackageId) -> impl Iterator<Item = &'a Package> {
+fn direct_deps_of<'a>(
+    metadata: &'a Metadata,
+    pkg_id: &'a PackageId,
+) -> impl Iterator<Item = &'a Package> {
     let resolve = metadata.resolve.as_ref().unwrap();
     let node = resolve.nodes.iter().find(|n| &n.id == pkg_id).unwrap();
     node.deps.iter().map(|dep| pkg_from_id(metadata, &dep.pkg))
 }
 
 fn check_rustfix(rust_metadata: &Metadata, cargo_metadata: &Metadata, bad: &mut bool) {
     let cargo = pkg_from_name(cargo_metadata, "cargo");
-    let cargo_rustfix = direct_deps_of(cargo_metadata, &cargo.id).find(|p| p.name == "rustfix").unwrap();
+    let cargo_rustfix =
+        direct_deps_of(cargo_metadata, &cargo.id).find(|p| p.name == "rustfix").unwrap();
 
     let compiletest = pkg_from_name(rust_metadata, "compiletest");
-    let compiletest_rustfix = direct_deps_of(rust_metadata, &compiletest.id).find(|p| p.name == "rustfix").unwrap();
+    let compiletest_rustfix =
+        direct_deps_of(rust_metadata, &compiletest.id).find(|p| p.name == "rustfix").unwrap();
 
     if cargo_rustfix.version != compiletest_rustfix.version {
         tidy_error!(