fix OOM when ty::Instance is used in query description

Author: Lukas Markeffsky

compiler/rustc_middle/src/ty/instance.rs

@@ -293,12 +293,16 @@ impl<'tcx> InstanceDef<'tcx> {
 fn fmt_instance(
     f: &mut fmt::Formatter<'_>,
     instance: &Instance<'_>,
-    type_length: rustc_session::Limit,
+    type_length: Option<rustc_session::Limit>,
 ) -> fmt::Result {
     ty::tls::with(|tcx| {
         let args = tcx.lift(instance.args).expect("could not lift for printing");
 
-        let mut cx = FmtPrinter::new_with_limit(tcx, Namespace::ValueNS, type_length);
+        let mut cx = if let Some(type_length) = type_length {
+            FmtPrinter::new_with_limit(tcx, Namespace::ValueNS, type_length)
+        } else {
+            FmtPrinter::new(tcx, Namespace::ValueNS)
+        };
         cx.print_def_path(instance.def_id(), args)?;
         let s = cx.into_buffer();
         f.write_str(&s)
@@ -324,13 +328,13 @@ pub struct ShortInstance<'a, 'tcx>(pub &'a Instance<'tcx>, pub usize);
 
 impl<'a, 'tcx> fmt::Display for ShortInstance<'a, 'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt_instance(f, self.0, rustc_session::Limit(self.1))
+        fmt_instance(f, self.0, Some(rustc_session::Limit(self.1)))
     }
 }
 
 impl<'tcx> fmt::Display for Instance<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        ty::tls::with(|tcx| fmt_instance(f, self, tcx.type_length_limit()))
+        fmt_instance(f, self, None)
     }
 }
 

tests/ui/resolve/auxiliary/suggest-constructor-cycle-error.rs

@@ -0,0 +1,12 @@
+mod m {
+    pub struct Uuid(());
+
+    impl Uuid {
+        pub fn encode_buffer() -> [u8; LENGTH] {
+            []
+        }
+    }
+    const LENGTH: usize = 0;
+}
+
+pub use m::Uuid;

tests/ui/resolve/suggest-constructor-cycle-error.rs

@@ -0,0 +1,10 @@
+// aux-build:suggest-constructor-cycle-error.rs
+//~^ cycle detected when getting the resolver for lowering [E0391]
+
+// Regression test for https://github.com/rust-lang/rust/issues/119625
+
+extern crate suggest_constructor_cycle_error as a;
+
+const CONST_NAME: a::Uuid = a::Uuid(());
+
+fn main() {}

tests/ui/resolve/suggest-constructor-cycle-error.stderr

@@ -0,0 +1,15 @@
+error[E0391]: cycle detected when getting the resolver for lowering
+   |
+   = note: ...which requires normalizing `[u8; suggest_constructor_cycle_error::::m::{impl#0}::encode_buffer::{constant#0}]`...
+note: ...which requires resolving instance `suggest_constructor_cycle_error::m::Uuid::encode_buffer::{constant#0}`...
+  --> $DIR/auxiliary/suggest-constructor-cycle-error.rs:5:40
+   |
+LL |         pub fn encode_buffer() -> [u8; LENGTH] {
+   |                                        ^^^^^^
+   = note: ...which requires calculating the lang items map...
+   = note: ...which again requires getting the resolver for lowering, completing the cycle
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0391`.