Match release stability for dated Rust toolchain releases

Author: JamieMagee

rust_toolchain/lib/dependabot/rust_toolchain/update_checker/latest_version_finder.rb

@@ -75,6 +75,13 @@ def filter_by_version_type(releases)
             # Check that the release version is in the same channel type
             next unless release_channel.channel_type == current_type
 
+            # For DatedStability channels, also check that the stability levels match
+            # e.g., "nightly-2025-08-19" should only match other "nightly-*" releases,
+            # not "stable-*" or "beta-*" releases
+            if current_type == ChannelType::DatedStability && release_channel.stability != current_channel.stability
+              next
+            end
+
             next release unless release_channel.channel_type == ChannelType::Version
 
             # For version channels, we need to ensure that the version format matches

rust_toolchain/spec/dependabot/rust_toolchain/update_checker/latest_version_finder_spec.rb

@@ -179,6 +179,58 @@
           .to match_array(%w(nightly-2023-12-25))
       end
     end
+
+    context "when dependency requirement is a nightly dated channel with mixed stability releases" do
+      let(:dependency_requirement) { "nightly-2025-08-19" }
+      let(:dependency_version) { "nightly-2025-08-19" }
+      let(:mock_versions) do
+        [
+          Dependabot::RustToolchain::Version.new("nightly-2025-08-01"),
+          Dependabot::RustToolchain::Version.new("nightly-2025-08-19"),
+          Dependabot::RustToolchain::Version.new("nightly-2025-08-20"),
+          Dependabot::RustToolchain::Version.new("stable-2025-08-07"),
+          Dependabot::RustToolchain::Version.new("stable-2025-08-14"),
+          Dependabot::RustToolchain::Version.new("beta-2025-08-10"),
+          Dependabot::RustToolchain::Version.new("1.72.0")
+        ]
+      end
+
+      it "only includes nightly releases, not stable or beta releases" do
+        package_details = version_finder.package_details
+        filtered_releases = version_finder.send(:apply_post_fetch_latest_versions_filter, package_details.releases)
+
+        expect(filtered_releases.map { |x| x.version.to_s })
+          .to match_array(%w(nightly-2025-08-01 nightly-2025-08-19 nightly-2025-08-20))
+        expect(filtered_releases.map { |x| x.version.to_s })
+          .not_to include("stable-2025-08-07", "stable-2025-08-14", "beta-2025-08-10", "1.72.0")
+      end
+    end
+
+    context "when dependency requirement is a stable dated channel with mixed stability releases" do
+      let(:dependency_requirement) { "stable-2025-08-07" }
+      let(:dependency_version) { "stable-2025-08-07" }
+      let(:mock_versions) do
+        [
+          Dependabot::RustToolchain::Version.new("nightly-2025-08-01"),
+          Dependabot::RustToolchain::Version.new("nightly-2025-08-19"),
+          Dependabot::RustToolchain::Version.new("stable-2025-08-07"),
+          Dependabot::RustToolchain::Version.new("stable-2025-08-14"),
+          Dependabot::RustToolchain::Version.new("stable-2025-08-21"),
+          Dependabot::RustToolchain::Version.new("beta-2025-08-10"),
+          Dependabot::RustToolchain::Version.new("1.72.0")
+        ]
+      end
+
+      it "only includes stable releases, not nightly or beta releases" do
+        package_details = version_finder.package_details
+        filtered_releases = version_finder.send(:apply_post_fetch_latest_versions_filter, package_details.releases)
+
+        expect(filtered_releases.map { |x| x.version.to_s })
+          .to match_array(%w(stable-2025-08-07 stable-2025-08-14 stable-2025-08-21))
+        expect(filtered_releases.map { |x| x.version.to_s })
+          .not_to include("nightly-2025-08-01", "nightly-2025-08-19", "beta-2025-08-10", "1.72.0")
+      end
+    end
   end
 
   describe "#apply_post_fetch_lowest_security_fix_versions_filter" do