In injection/inversion, consider all template-polymorphic types as injectable.

In particular singleton inductive types are considered injectable,
even in the absence of the option "Set Keep Proof Equalities".

This fixes #3125 (and #4560, #6273).

2 files changed, 28 insertions, 1 deletions

diff --git a/tactics/equality.ml b/tactics/equality.ml
index c36ad980e..0d6263246 100644
--- a/tactics/equality.ml
+++ b/tactics/equality.ml
@@ -739,7 +739,7 @@ let keep_proof_equalities = function
 let find_positions env sigma ~keep_proofs ~no_discr t1 t2 =
   let project env sorts posn t1 t2 =
     let ty1 = get_type_of env sigma t1 in
-    let s = get_sort_family_of env sigma ty1 in
+    let s = get_sort_family_of ~truncation_style:true env sigma ty1 in
     if Sorts.List.mem s sorts
     then [(List.rev posn,t1,t2)] else []
   in
diff --git a/test-suite/bugs/closed/3125.v b/test-suite/bugs/closed/3125.v
new file mode 100644
index 000000000..797146174
--- /dev/null
+++ b/test-suite/bugs/closed/3125.v
@@ -0,0 +1,27 @@
+(* Not considering singleton template-polymorphic inductive types as
+   propositions for injection/inversion *)
+
+(* This is also #4560 and #6273 *)
+
+Inductive foo := foo_1.
+
+Goal forall (a b : foo), Some a = Some b -> a = b.
+Proof.
+  intros a b H.
+  inversion H.
+  reflexivity.
+Qed.
+
+(* Check that Prop is not concerned *)
+
+Inductive bar : Prop := bar_1.
+
+Goal
+  forall (a b : bar),
+    Some a = Some b ->
+    a = b.
+Proof.
+  intros a b H.
+  inversion H.
+  Fail reflexivity.
+Abort.