Fix #6257: anomaly with Printing Projections and Context.

Constrextern.explicitize expected that if implicits were declared they
would be declared at least up to the principal argument of the
projection, but Context/discharge of implicits does not preserve this.

Note the anomaly only happens with primitive projections DISABLED in
recent Coqs (>=8.8).

Implicit argument experts may consider whether ensuring enough
implicits are declared would be better.

2 files changed, 13 insertions, 0 deletions

diff --git a/test-suite/output/Projections.out b/test-suite/output/Projections.out
new file mode 100644
index 000000000..e9c28faf1
--- /dev/null
+++ b/test-suite/output/Projections.out
@@ -0,0 +1,2 @@
+fun S : store => S.(store_funcs)
+     : store -> host_func
diff --git a/test-suite/output/Projections.v b/test-suite/output/Projections.v
new file mode 100644
index 000000000..098a518dc
--- /dev/null
+++ b/test-suite/output/Projections.v
@@ -0,0 +1,11 @@
+
+Set Printing Projections.
+
+Class HostFunction := host_func : Type.
+
+Section store.
+  Context `{HostFunction}.
+  Record store := { store_funcs : host_func }.
+End store.
+
+Check (fun (S:@store nat) => S.(store_funcs)).