fix(cargo): Add a warning on package and project in the same Cargo.toml

src/cargo/util/toml/mod.rs

@@ -1578,8 +1578,19 @@ impl TomlManifest {
         let cargo_features = me.cargo_features.as_ref().unwrap_or(&empty);
         let features = Features::new(cargo_features, config, &mut warnings, source_id.is_path())?;
 
-        let package = me.project.clone().or_else(|| me.package.clone());
-        let package = &mut package.ok_or_else(|| anyhow!("no `package` section found"))?;
+        let mut package = match (&me.package, &me.project) {
+            (Some(_), Some(project)) => {
+                config.shell().warn(format!(
+                    "manifest at `{}` contains both `project` and `package`, \
+                    this could become a hard error in the future",
+                    package_root.display()
+                ))?;
+                project.clone()
+            }
+            (Some(package), None) => package.clone(),
+            (None, Some(project)) => project.clone(),
+            (None, None) => bail!("no `package` section found"),
+        };
 
         let workspace_config = match (me.workspace.as_ref(), package.workspace.as_ref()) {
             (Some(toml_config), None) => {

tests/testsuite/check.rs

@@ -1024,3 +1024,33 @@ fn rustc_workspace_wrapper_excludes_published_deps() {
         .with_stdout_does_not_contain("WRAPPER CALLED: rustc --crate-name baz [..]")
         .run();
 }
+
+#[cargo_test]
+fn warn_manifest_package_and_project() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+
+                [project]
+                name = "foo"
+                version = "0.0.1"
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("check")
+        .with_status(0)
+        .with_stderr(
+            "\
+[WARNING] manifest at `[CWD]` contains both `project` and `package`, this could become a hard error in the future
+[CHECKING] foo v0.0.1 ([CWD])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
+",
+        )
+        .run();
+}