Do not set depth to 0 in fully_expand_fragment

compiler/rustc_expand/src/expand.rs

@@ -427,7 +427,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
         let orig_expansion_data = self.cx.current_expansion.clone();
         let orig_force_mode = self.cx.force_mode;
-        self.cx.current_expansion.depth = 0;
 
         // Collect all macro invocations and replace them with placeholders.
         let (mut fragment_with_placeholders, mut invocations) =
@@ -488,6 +487,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             };
 
             let ExpansionData { depth, id: expn_id, .. } = invoc.expansion_data;
+            let depth = depth - orig_expansion_data.depth;
             self.cx.current_expansion = invoc.expansion_data.clone();
             self.cx.force_mode = force;
 

src/test/ui/macros/issue-84632-eager-expansion-recursion-limit.rs

@@ -0,0 +1,16 @@
+// Regression test for #84632: Recursion limit is ignored
+// for builtin macros that eagerly expands.
+
+#![recursion_limit = "15"]
+macro_rules! a {
+    () => ("");
+    (A) => (concat!("", a!()));
+    (A, $($A:ident),*) => (concat!("", a!($($A),*)))
+    //~^ ERROR recursion limit reached
+    //~| HELP consider adding
+}
+
+fn main() {
+    a!(A, A, A, A, A);
+    a!(A, A, A, A, A, A, A, A, A, A, A);
+}

src/test/ui/macros/issue-84632-eager-expansion-recursion-limit.stderr

@@ -0,0 +1,14 @@
+error: recursion limit reached while expanding `concat!`
+  --> $DIR/issue-84632-eager-expansion-recursion-limit.rs:8:28
+   |
+LL |     (A, $($A:ident),*) => (concat!("", a!($($A),*)))
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     a!(A, A, A, A, A, A, A, A, A, A, A);
+   |     ------------------------------------ in this macro invocation
+   |
+   = help: consider adding a `#![recursion_limit="30"]` attribute to your crate (`issue_84632_eager_expansion_recursion_limit`)
+   = note: this error originates in the macro `a` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+