Add function_like_proc_macro_missing lint (#1021)

Addresses a checkbox in #946

---------

Co-authored-by: Predrag Gruevski <[email protected]>

src/lints/function_like_proc_macro_missing.ron

@@ -0,0 +1,42 @@
+SemverQuery(
+    id: "function_like_proc_macro_missing",
+    human_readable_name: "function-like proc macro removed",
+    description: "A function-like procedural macro that previously existed has been removed.",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on FunctionLikeProcMacro {
+                        macro_name: name @output @tag
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        
+                        # Get span info from the baseline for error reporting
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+            
+            current @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
+                item {
+                    ... on FunctionLikeProcMacro {
+                        name @filter(op: "=", value: ["%macro_name"])
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "zero": 0,
+    },
+    error_message: "A function-like procedural macro has been removed. Any code that invokes this macro will fail to compile.",
+    per_result_error_template: Some("macro {{macro_name}} in file {{span_filename}}:{{span_begin_line}}"),
+    witness: None,
+)

src/query.rs

@@ -1079,6 +1079,7 @@ add_lints!(
     function_changed_abi,
     function_const_removed,
     function_export_name_changed,
+    function_like_proc_macro_missing,
     function_missing,
     function_must_use_added,
     function_now_doc_hidden,

test_crates/function_like_proc_macro_missing/new/Cargo.toml

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

test_crates/function_like_proc_macro_missing/new/src/lib.rs

@@ -0,0 +1,20 @@
+use proc_macro::TokenStream;
+
+// make_answer is removed
+
+// Keep this to verify we don't have false positives
+#[proc_macro]
+pub fn another_macro(_item: TokenStream) -> TokenStream {
+    "fn other() -> u32 { 0 }".parse().unwrap()
+}
+
+// Keep other macro types to verify we don't detect their changes
+#[proc_macro_derive(MyDerive)]
+pub fn my_derive(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+#[proc_macro_attribute]
+pub fn my_attribute(_attr: TokenStream, _item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}

test_crates/function_like_proc_macro_missing/old/Cargo.toml

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

test_crates/function_like_proc_macro_missing/old/src/lib.rs

@@ -0,0 +1,23 @@
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn make_answer(_item: TokenStream) -> TokenStream {
+    "fn answer() -> u32 { 42 }".parse().unwrap()
+}
+
+// Will keep this one to ensure we don't have false positives
+#[proc_macro]
+pub fn another_macro(_item: TokenStream) -> TokenStream {
+    "fn other() -> u32 { 0 }".parse().unwrap()
+}
+
+// Other kinds of proc macros that should not trigger this lint
+#[proc_macro_derive(MyDerive)]
+pub fn my_derive(_item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
+
+#[proc_macro_attribute]
+pub fn my_attribute(_attr: TokenStream, _item: TokenStream) -> TokenStream {
+    TokenStream::new()
+}

test_outputs/query_execution/function_like_proc_macro_missing.snap

@@ -0,0 +1,14 @@
+---
+source: src/query.rs
+expression: "&query_execution_results"
+snapshot_kind: text
+---
+{
+  "./test_crates/function_like_proc_macro_missing/": [
+    {
+      "macro_name": String("make_answer"),
+      "span_begin_line": Uint64(4),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
+}