new lint: trait_associated_const_marked_deprecated (#1100)

part of: #57

src/lints/trait_associated_const_marked_deprecated.ron

@@ -0,0 +1,61 @@
+SemverQuery(
+    id: "trait_associated_const_marked_deprecated",
+    human_readable_name: "trait associated constant #[deprecated] added",
+    description: "A trait's associated constant has been newly marked with #[deprecated].",
+    required_update: Minor,
+    lint_level: Deny,
+    reference_link: Some("https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute"),
+    query: r#"
+    {
+        CrateDiff {
+            current {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        name @output
+
+                        importable_path {
+                            path @tag @output
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        associated_constant {
+                            associated_constant: name @output @tag
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            deprecated @filter(op: "=", value: ["$true"])
+
+                            span_: span @optional {
+                                filename @output
+                                begin_line @output
+                            }
+                        }
+                    }
+                }
+            }
+            baseline {
+                item {
+                    ... on Trait {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        associated_constant {
+                            name @filter(op: "=", value: ["%associated_constant"])
+                            public_api_eligible @filter(op: "=", value: ["$true"])
+                            deprecated @filter(op: "!=", value: ["$true"])
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "true": true,
+    },
+    error_message: "A trait associated constant is now #[deprecated]. Downstream crates will get a compiler warning when using it.",
+    per_result_error_template: Some("associated constant {{associated_constant}} in trait {{join \"::\" path}} in {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -1214,6 +1214,7 @@ add_lints!(
     trait_allows_fewer_generic_type_params,
     trait_associated_const_added,
     trait_associated_const_default_removed,
+    trait_associated_const_marked_deprecated,
     trait_associated_const_now_doc_hidden,
     trait_associated_type_added,
     trait_associated_type_default_removed,

test_crates/trait_associated_const_marked_deprecated/new/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "trait_associated_const_marked_deprecated"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/trait_associated_const_marked_deprecated/new/src/lib.rs

@@ -0,0 +1,44 @@
+pub trait TraitWithConstToBeDeprecated {
+    // These constants are now deprecated and should be reported
+    #[deprecated]
+    const CONST_TO_DEPRECATED: i32 = 42;
+
+    #[deprecated = "This constant is deprecated"]
+    const CONST_TO_DEPRECATED_MESSAGE: &'static str = "hello";
+
+    // These constants should not trigger the lint
+    const CONST_STAYS_NORMAL: bool = true;
+
+    #[deprecated]
+    const CONST_ALREADY_DEPRECATED: u32 = 100;
+
+    #[deprecated = "New message"]
+    const CONST_MESSAGE_CHANGES: char = 'x';
+}
+
+// Changes to private trait constants should not be reported
+trait PrivateTrait {
+    #[deprecated]
+    const PRIVATE_CONST_TO_DEPRECATED: i32 = 0;
+}
+
+#[deprecated]
+pub trait DeprecatedTrait {
+    // Adding deprecated to a constant in an already deprecated trait should not be reported
+    #[deprecated]
+    const CONST_IN_DEPRECATED_TRAIT: i32 = 1;
+}
+
+// Hidden trait - changes to its constants should not be reported
+#[doc(hidden)]
+pub trait HiddenTrait {
+    #[deprecated]
+    const CONST_BECOMES_DEPRECATED: i32 = 2;
+}
+
+// Public trait with hidden constant should not be reported
+pub trait PublicTraitWithHiddenConst {
+    #[doc(hidden)]
+    #[deprecated]
+    const HIDDEN_CONST_BECOMES_DEPRECATED: i32 = 3;
+}

test_crates/trait_associated_const_marked_deprecated/old/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "trait_associated_const_marked_deprecated"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/trait_associated_const_marked_deprecated/old/src/lib.rs

@@ -0,0 +1,39 @@
+pub trait TraitWithConstToBeDeprecated {
+    // This associated constant will be marked deprecated
+    const CONST_TO_DEPRECATED: i32 = 42;
+
+    // This associated constant will be marked deprecated with a message
+    const CONST_TO_DEPRECATED_MESSAGE: &'static str = "hello";
+
+    // These constants should not trigger the lint
+    const CONST_STAYS_NORMAL: bool = true;
+
+    #[deprecated]
+    const CONST_ALREADY_DEPRECATED: u32 = 100;
+
+    #[deprecated = "Old message"]
+    const CONST_MESSAGE_CHANGES: char = 'x';
+}
+
+// Changes to private trait constants should not be reported
+trait PrivateTrait {
+    const PRIVATE_CONST_TO_DEPRECATED: i32 = 0;
+}
+
+#[deprecated]
+pub trait DeprecatedTrait {
+    // Adding deprecated to a constant in an already deprecated trait should not be reported
+    const CONST_IN_DEPRECATED_TRAIT: i32 = 1;
+}
+
+// Hidden trait - changes to its constants should not be reported
+#[doc(hidden)]
+pub trait HiddenTrait {
+    const CONST_BECOMES_DEPRECATED: i32 = 2;
+}
+
+// Public trait with hidden constant should not be reported
+pub trait PublicTraitWithHiddenConst {
+    #[doc(hidden)]
+    const HIDDEN_CONST_BECOMES_DEPRECATED: i32 = 3;
+}

test_outputs/query_execution/trait_associated_const_marked_deprecated.snap

@@ -0,0 +1,30 @@
+---
+source: src/query.rs
+expression: "&query_execution_results"
+---
+{
+  "./test_crates/trait_associated_const_marked_deprecated/": [
+    {
+      "associated_constant": String("CONST_TO_DEPRECATED"),
+      "name": String("TraitWithConstToBeDeprecated"),
+      "path": List([
+        String("trait_associated_const_marked_deprecated"),
+        String("TraitWithConstToBeDeprecated"),
+      ]),
+      "span_begin_line": Uint64(4),
+      "span_filename": String("src/lib.rs"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "associated_constant": String("CONST_TO_DEPRECATED_MESSAGE"),
+      "name": String("TraitWithConstToBeDeprecated"),
+      "path": List([
+        String("trait_associated_const_marked_deprecated"),
+        String("TraitWithConstToBeDeprecated"),
+      ]),
+      "span_begin_line": Uint64(7),
+      "span_filename": String("src/lib.rs"),
+      "visibility_limit": String("public"),
+    },
+  ],
+}