Add proc_macro_now_doc_hidden lint.

Resolves #946.

src/lints/proc_macro_now_doc_hidden.ron

@@ -0,0 +1,50 @@
+SemverQuery(
+    id: "proc_macro_now_doc_hidden",
+    human_readable_name: "proc macro became #[doc(hidden)]",
+    description: "A procedural macro has become #[doc(hidden)] and is no longer public API.",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://doc.rust-lang.org/rustdoc/write-documentation/the-doc-attribute.html#hidden"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on ProcMacro {
+                        kind: __typename @output @tag
+                        visibility_limit @filter(op: "=", value: ["$public"])
+
+                        importable_path {
+                            path @output @tag
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on ProcMacro {
+                        __typename @filter(op: "=", value: ["%kind"])
+                        name @output
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "!=", value: ["$true"])
+                        }
+
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "true": true,
+    },
+    error_message: "A public procedural macro is now #[doc(hidden)], removing it from the crate's public API.",
+    per_result_error_template: Some("proc macro {{name}} in file {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -1172,6 +1172,7 @@ add_lints!(
     method_parameter_count_changed,
     module_missing,
     non_exhaustive_struct_changed_type,
+    proc_macro_now_doc_hidden,
     pub_module_level_const_missing,
     pub_module_level_const_now_doc_hidden,
     pub_static_missing,

test_crates/proc_macro_now_doc_hidden/new/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+publish = false
+name = "proc_macro_now_doc_hidden"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]

test_crates/proc_macro_now_doc_hidden/new/src/lib.rs

@@ -0,0 +1,22 @@
+use proc_macro::TokenStream;
+
+// An attribute macro we'll hide. Should trigger the lint.
+#[doc(hidden)]
+#[proc_macro_attribute]
+pub fn logging(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    item
+}
+
+// A function-like macro we'll hide. Should trigger the lint.
+#[doc(hidden)]
+#[proc_macro]
+pub fn sql(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+// A derive macro we'll hide. Should trigger the lint.
+#[doc(hidden)]
+#[proc_macro_derive(MyDerive)]
+pub fn my_derive(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}

test_crates/proc_macro_now_doc_hidden/old/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+publish = false
+name = "proc_macro_now_doc_hidden"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]

test_crates/proc_macro_now_doc_hidden/old/src/lib.rs

@@ -0,0 +1,40 @@
+use proc_macro::TokenStream;
+
+// An attribute macro we'll hide. Should trigger the lint.
+#[proc_macro_attribute]
+pub fn logging(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    item
+}
+
+// A function-like macro we'll hide. Should trigger the lint.
+#[proc_macro]
+pub fn sql(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+// A derive macro we'll hide. Should trigger the lint.
+#[proc_macro_derive(MyDerive)]
+pub fn my_derive(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+// A hidden attribute macro we'll delete. Shouldn't trigger any lint.
+#[doc(hidden)]
+#[proc_macro_attribute]
+pub fn hidden_logging(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    item
+}
+
+// A hidden function-like macro we'll delete. Shouldn't trigger any lint.
+#[doc(hidden)]
+#[proc_macro]
+pub fn hidden_sql(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+// A hidden derive macro we'll delete. Shouldn't trigger any lint.
+#[doc(hidden)]
+#[proc_macro_derive(MyHiddenDerive)]
+pub fn hidden_derive(item: TokenStream) -> TokenStream {
+    item
+}

test_outputs/query_execution/proc_macro_now_doc_hidden.snap

@@ -0,0 +1,39 @@
+---
+source: src/query.rs
+expression: "&query_execution_results"
+snapshot_kind: text
+---
+{
+  "./test_crates/proc_macro_now_doc_hidden/": [
+    {
+      "kind": String("AttributeProcMacro"),
+      "name": String("logging"),
+      "path": List([
+        String("proc_macro_now_doc_hidden"),
+        String("logging"),
+      ]),
+      "span_begin_line": Uint64(6),
+      "span_filename": String("src/lib.rs"),
+    },
+    {
+      "kind": String("FunctionLikeProcMacro"),
+      "name": String("sql"),
+      "path": List([
+        String("proc_macro_now_doc_hidden"),
+        String("sql"),
+      ]),
+      "span_begin_line": Uint64(13),
+      "span_filename": String("src/lib.rs"),
+    },
+    {
+      "kind": String("DeriveProcMacro"),
+      "name": String("MyDerive"),
+      "path": List([
+        String("proc_macro_now_doc_hidden"),
+        String("MyDerive"),
+      ]),
+      "span_begin_line": Uint64(20),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
+}