Rollup merge of #107532 - compiler-errors:erase-regions-in-uninhabited, r=jackh726

Erase regions before doing uninhabited check in borrowck

~Also, fingerprint query keys/values when debug assertions are enabled. This should make it easier to check for issues like this without `-Cincremental`, and make UI tests a bit cleaner.~ edit: moving that to a separate PR

Fixes #107505

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1484,7 +1484,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
             }
             None => {
-                if !sig.output().is_privately_uninhabited(self.tcx(), self.param_env) {
+                // The signature in this call can reference region variables,
+                // so erase them before calling a query.
+                let output_ty = self.tcx().erase_regions(sig.output());
+                if !output_ty.is_privately_uninhabited(self.tcx(), self.param_env) {
                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
                 }
             }

tests/ui/uninhabited/issue-107505.rs

@@ -0,0 +1,18 @@
+// compile-flags: --crate-type=lib
+// check-pass
+
+// Make sure we don't pass inference variables to uninhabitedness checks in borrowck
+
+struct Command<'s> {
+    session: &'s (),
+    imp: std::convert::Infallible,
+}
+
+fn command(_: &()) -> Command<'_> {
+    unreachable!()
+}
+
+fn with_session<'s>(a: &std::process::Command, b: &'s ()) -> Command<'s> {
+    a.get_program();
+    command(b)
+}