feat(fix): Add features for unused deps on Edition 2024

src/cargo/ops/fix.rs

@@ -53,12 +53,13 @@ use tracing::{debug, trace, warn};
 use crate::core::compiler::RustcTargetData;
 use crate::core::resolver::features::{DiffMap, FeatureOpts, FeatureResolver, FeaturesFor};
 use crate::core::resolver::{HasDevUnits, Resolve, ResolveBehavior};
-use crate::core::PackageIdSpecQuery as _;
 use crate::core::{Edition, MaybePackage, Package, PackageId, Workspace};
+use crate::core::{FeatureValue, PackageIdSpecQuery as _};
 use crate::ops::resolve::WorkspaceResolve;
 use crate::ops::{self, CompileOptions};
 use crate::util::diagnostic_server::{Message, RustfixDiagnosticServer};
 use crate::util::errors::CargoResult;
+use crate::util::interning::InternedString;
 use crate::util::GlobalContext;
 use crate::util::{existing_vcs_repo, LockServer, LockServerClient};
 use crate::{drop_eprint, drop_eprintln};
@@ -253,6 +254,7 @@ fn migrate_manifests(ws: &Workspace<'_>, pkgs: &[&Package]) -> CargoResult<()> {
             let mut fixes = 0;
 
             let root = document.as_table_mut();
+            fixes += add_feature_for_unused_deps(pkg, root);
             if rename_table(root, "project", "package") {
                 fixes += 1;
             }
@@ -287,6 +289,45 @@ fn rename_table(parent: &mut dyn toml_edit::TableLike, old: &str, new: &str) ->
     true
 }
 
+fn add_feature_for_unused_deps(pkg: &Package, parent: &mut dyn toml_edit::TableLike) -> usize {
+    let manifest = pkg.manifest();
+
+    let activated_opt_deps = manifest
+        .resolved_toml()
+        .features()
+        .map(|map| {
+            map.values()
+                .flatten()
+                .filter_map(|f| match FeatureValue::new(InternedString::new(f)) {
+                    FeatureValue::Dep { dep_name } => Some(dep_name.as_str()),
+                    _ => None,
+                })
+                .collect::<HashSet<_>>()
+        })
+        .unwrap_or_default();
+
+    let mut fixes = 0;
+    for dep in manifest.dependencies() {
+        let dep_name_in_toml = dep.name_in_toml();
+        if dep.is_optional() && !activated_opt_deps.contains(dep_name_in_toml.as_str()) {
+            fixes += 1;
+            if let Some(features) = parent
+                .entry("features")
+                .or_insert(toml_edit::table())
+                .as_table_like_mut()
+            {
+                features.insert(
+                    dep_name_in_toml.as_str(),
+                    toml_edit::Item::Value(toml_edit::Value::Array(toml_edit::Array::from_iter(
+                        &[format!("dep:{}", dep_name_in_toml)],
+                    ))),
+                );
+            }
+        }
+    }
+    fixes
+}
+
 fn check_resolver_change(ws: &Workspace<'_>, opts: &FixOptions) -> CargoResult<()> {
     let root = ws.root_maybe();
     match root {

tests/testsuite/fix.rs

@@ -2049,3 +2049,138 @@ edition = "2021"
 "#
     );
 }
+
+#[cargo_test]
+fn add_feature_for_unused_dep() {
+    Package::new("bar", "0.1.0").publish();
+    Package::new("baz", "0.1.0").publish();
+    Package::new("target-dep", "0.1.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bar = { version = "0.1.0", optional = true }
+
+[build-dependencies]
+baz = { version = "0.1.0", optional = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+target-dep = { version = "0.1.0", optional = true }
+"#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("fix --edition --allow-no-vcs")
+        .masquerade_as_nightly_cargo(&["edition2024"])
+        .with_stderr(
+            "\
+[MIGRATING] Cargo.toml from 2021 edition to 2024
+[FIXED] Cargo.toml (3 fixes)
+[UPDATING] `dummy-registry` index
+[LOCKING] 4 packages to latest compatible versions
+[CHECKING] foo v0.1.0 ([CWD])
+[MIGRATING] src/lib.rs from 2021 edition to 2024
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [..]s
+",
+        )
+        .run();
+    assert_eq!(
+        p.read_file("Cargo.toml"),
+        r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bar = { version = "0.1.0", optional = true }
+
+[build-dependencies]
+baz = { version = "0.1.0", optional = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+target-dep = { version = "0.1.0", optional = true }
+
+[features]
+bar = ["dep:bar"]
+baz = ["dep:baz"]
+target-dep = ["dep:target-dep"]
+"#
+    );
+}
+
+#[cargo_test]
+fn add_feature_for_unused_dep_existing_table() {
+    Package::new("bar", "0.1.0").publish();
+    Package::new("baz", "0.1.0").publish();
+    Package::new("target-dep", "0.1.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bar = { version = "0.1.0", optional = true }
+
+[build-dependencies]
+baz = { version = "0.1.0", optional = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+target-dep = { version = "0.1.0", optional = true }
+
+[features]
+target-dep = ["dep:target-dep"]
+"#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("fix --edition --allow-no-vcs")
+        .masquerade_as_nightly_cargo(&["edition2024"])
+        .with_stderr(
+            "\
+[MIGRATING] Cargo.toml from 2021 edition to 2024
+[FIXED] Cargo.toml (2 fixes)
+[UPDATING] `dummy-registry` index
+[LOCKING] 4 packages to latest compatible versions
+[CHECKING] foo v0.1.0 ([CWD])
+[MIGRATING] src/lib.rs from 2021 edition to 2024
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [..]s
+",
+        )
+        .run();
+    assert_eq!(
+        p.read_file("Cargo.toml"),
+        r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bar = { version = "0.1.0", optional = true }
+
+[build-dependencies]
+baz = { version = "0.1.0", optional = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+target-dep = { version = "0.1.0", optional = true }
+
+[features]
+target-dep = ["dep:target-dep"]
+bar = ["dep:bar"]
+baz = ["dep:baz"]
+"#
+    );
+}