Merge #11360

11360: feat: Support `#![recursion_limit]` attribute r=Veykril a=WaffleLapkin

![Peek 2022-01-28 02-33](https://user-images.githubusercontent.com/38225716/151508617-ac802b53-f088-4cac-b260-2cd077f3d32c.gif)

Resolves #8640

`@matklad` thanks, for the instructions, they were very helpful :)

Co-authored-by: Maybe Waffle <waffle.lapkin@gmail.com>

crates/hir_def/src/body.rs

@@ -54,12 +54,6 @@ pub struct Expander {
     recursion_limit: usize,
 }
 
-#[cfg(test)]
-static EXPANSION_RECURSION_LIMIT: Limit = Limit::new(32);
-
-#[cfg(not(test))]
-static EXPANSION_RECURSION_LIMIT: Limit = Limit::new(128);
-
 impl CfgExpander {
     pub(crate) fn new(
         db: &dyn DefDatabase,
@@ -101,7 +95,7 @@ impl Expander {
         db: &dyn DefDatabase,
         macro_call: ast::MacroCall,
     ) -> Result<ExpandResult<Option<(Mark, T)>>, UnresolvedMacro> {
-        if EXPANSION_RECURSION_LIMIT.check(self.recursion_limit + 1).is_err() {
+        if self.recursion_limit(db).check(self.recursion_limit + 1).is_err() {
             cov_mark::hit!(your_stack_belongs_to_me);
             return Ok(ExpandResult::str_err(
                 "reached recursion limit during macro expansion".into(),
@@ -222,6 +216,17 @@ impl Expander {
         let file_local_id = self.ast_id_map.ast_id(item);
         AstId::new(self.current_file_id, file_local_id)
     }
+
+    fn recursion_limit(&self, db: &dyn DefDatabase) -> Limit {
+        let limit = db.crate_limits(self.cfg_expander.krate).recursion_limit as _;
+
+        #[cfg(not(test))]
+        return Limit::new(limit);
+
+        // Without this, `body::tests::your_stack_belongs_to_me` stack-overflows in debug
+        #[cfg(test)]
+        return Limit::new(std::cmp::min(32, limit));
+    }
 }
 
 #[derive(Debug)]

crates/hir_def/src/body/tests.rs

@@ -61,6 +61,24 @@ fn main() { n_nuple!(1,2,3); }
     );
 }
 
+#[test]
+fn recursion_limit() {
+    cov_mark::check!(your_stack_belongs_to_me);
+
+    lower(
+        r#"
+#![recursion_limit = "2"]
+macro_rules! n_nuple {
+    ($e:tt) => ();
+    ($first:tt $($rest:tt)*) => {{
+        n_nuple!($($rest)*)
+    }};
+}
+fn main() { n_nuple!(1,2,3); }
+"#,
+    );
+}
+
 #[test]
 fn macro_resolve() {
     // Regression test for a path resolution bug introduced with inner item handling.

crates/hir_def/src/db.rs

@@ -157,9 +157,26 @@ pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
 
     #[salsa::invoke(visibility::function_visibility_query)]
     fn function_visibility(&self, def: FunctionId) -> Visibility;
+
+    #[salsa::transparent]
+    fn crate_limits(&self, crate_id: CrateId) -> CrateLimits;
 }
 
 fn crate_def_map_wait(db: &dyn DefDatabase, krate: CrateId) -> Arc<DefMap> {
     let _p = profile::span("crate_def_map:wait");
     db.crate_def_map_query(krate)
 }
+
+pub struct CrateLimits {
+    /// The maximum depth for potentially infinitely-recursive compile-time operations like macro expansion or auto-dereference.
+    pub recursion_limit: u32,
+}
+
+fn crate_limits(db: &dyn DefDatabase, crate_id: CrateId) -> CrateLimits {
+    let def_map = db.crate_def_map(crate_id);
+
+    CrateLimits {
+        // 128 is the default in rustc.
+        recursion_limit: def_map.recursion_limit().unwrap_or(128),
+    }
+}

crates/hir_def/src/nameres.rs

@@ -114,6 +114,7 @@ pub struct DefMap {
     registered_tools: Vec<SmolStr>,
 
     edition: Edition,
+    recursion_limit: Option<u32>,
     diagnostics: Vec<DefDiagnostic>,
 }
 
@@ -272,6 +273,7 @@ impl DefMap {
             block: None,
             krate,
             edition,
+            recursion_limit: None,
             extern_prelude: FxHashMap::default(),
             exported_proc_macros: FxHashMap::default(),
             prelude: None,
@@ -461,6 +463,7 @@ impl DefMap {
             registered_tools,
             block: _,
             edition: _,
+            recursion_limit: _,
             krate: _,
             prelude: _,
             root: _,
@@ -482,6 +485,10 @@ impl DefMap {
     pub fn diagnostics(&self) -> &[DefDiagnostic] {
         self.diagnostics.as_slice()
     }
+
+    pub fn recursion_limit(&self) -> Option<u32> {
+        self.recursion_limit
+    }
 }
 
 impl ModuleData {

crates/hir_def/src/nameres/collector.rs

@@ -271,6 +271,17 @@ impl DefCollector<'_> {
                     None => continue,
                 };
 
+                if *attr_name == hir_expand::name![recursion_limit] {
+                    if let Some(input) = &attr.input {
+                        if let AttrInput::Literal(limit) = &**input {
+                            if let Ok(limit) = limit.parse() {
+                                self.def_map.recursion_limit = Some(limit);
+                            }
+                        }
+                    }
+                    continue;
+                }
+
                 let attr_is_register_like = *attr_name == hir_expand::name![register_attr]
                     || *attr_name == hir_expand::name![register_tool];
                 if !attr_is_register_like {

crates/hir_expand/src/name.rs

@@ -270,6 +270,7 @@ pub mod known {
         global_allocator,
         test,
         test_case,
+        recursion_limit,
         // Safe intrinsics
         abort,
         add_with_overflow,