Implement new_struct_added lint

src/lints/new_struct_added.ron

@@ -0,0 +1,43 @@
+SemverQuery(
+    id: "new_struct_added",
+    human_readable_name: "new struct added",
+    description: "A new public struct has been exposed.",
+    required_update: Minor,
+
+    // TODO: Change the reference link to point to the cargo semver reference
+    //       once it has a section on attribute #[must_use].
+    reference_link: Some("https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"),
+    query: r#"
+    {
+        CrateDiff {
+            current {
+                item {
+                    ... on Struct {
+                        name @tag(name: "new_crate_name") @output(name: "new_struct_added_name")
+                        visibility_limit @filter(op: "=", value: ["$public"])
+
+                        span_: span {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+
+            baseline {
+                item @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
+                    ... on Struct {
+                        name @filter(op: "=", value: ["%new_crate_name"])
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "zero": 0,
+    },
+    error_message: "A new struct has been added to externally exposed API, this requires a minor version bump.",
+    per_result_error_template: Some("struct {{new_struct_added_name}} in {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -501,4 +501,5 @@ add_lints!(
     enum_tuple_variant_field_missing,
     enum_tuple_variant_field_added,
     trait_removed_supertrait,
+    new_struct_added,
 );

test_crates/new_struct_added/new/Cargo.toml

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

test_crates/new_struct_added/new/src/lib.rs

@@ -0,0 +1,2 @@
+struct A;
+pub struct B;

test_crates/new_struct_added/old/Cargo.toml

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

test_crates/new_struct_added/old/src/lib.rs

@@ -0,0 +1 @@
+struct A;

test_outputs/new_struct_added.output.ron

@@ -0,0 +1,66 @@
+{
+    "./test_crates/inherent_method_must_use_added/": [
+        {
+            "new_struct_added_name": String("EnumToStructWithMustUseMethods"),
+            "span_begin_line": Uint64(8),
+            "span_filename": String("src/item_type_changed_inherent_method_must_use_added.rs"),
+        },
+        {
+            "new_struct_added_name": String("UnionToStructWithMustUseMethods"),
+            "span_begin_line": Uint64(141),
+            "span_filename": String("src/item_type_changed_inherent_method_must_use_added.rs"),
+        },
+        {
+            "new_struct_added_name": String("NewStructWithMustUseMethods"),
+            "span_begin_line": Uint64(68),
+            "span_filename": String("src/struct_inherent_method_must_use_added.rs"),
+        },
+    ],
+    "./test_crates/method_moved_to_trait_must_use_added/": [
+        {
+            "new_struct_added_name": String("NewStructWithTraitMustUseMethods"),
+            "span_begin_line": Uint64(147),
+            "span_filename": String("src/struct_method_moved_to_trait_must_use_added.rs"),
+        },
+    ],
+    "./test_crates/move_item_and_reexport/": [
+        {
+            "new_struct_added_name": String("HasBeenRenamedTypedefReexport"),
+            "span_begin_line": Uint64(25),
+            "span_filename": String("src/lib.rs"),
+        },
+        {
+            "new_struct_added_name": String("HasBeenRenamedTypedefWithGenericsReexport"),
+            "span_begin_line": Uint64(27),
+            "span_filename": String("src/lib.rs"),
+        },
+    ],
+    "./test_crates/new_struct_added/": [
+        {
+            "new_struct_added_name": String("B"),
+            "span_begin_line": Uint64(2),
+            "span_filename": String("src/lib.rs"),
+        },
+    ],
+    "./test_crates/nonbreaking_item_rename/": [
+        {
+            "new_struct_added_name": String("NewName"),
+            "span_begin_line": Uint64(2),
+            "span_filename": String("src/lib.rs"),
+        },
+    ],
+    "./test_crates/struct_must_use_added/": [
+        {
+            "new_struct_added_name": String("MustUseNewStruct"),
+            "span_begin_line": Uint64(60),
+            "span_filename": String("src/lib.rs"),
+        },
+    ],
+    "./test_crates/type_marked_deprecated/": [
+        {
+            "new_struct_added_name": String("DeprecatedNewStruct"),
+            "span_begin_line": Uint64(57),
+            "span_filename": String("src/structs.rs"),
+        },
+    ],
+}