Take Suggest Proof Using outside the kernel.

Also add an output test for Suggest Proof Using.

This changes the .aux output: instead of getting a key
>context_used "$hyps;$suggest"
where $hyps is a list of the used hypotheses and $suggest is the
;-separated suggestions (or the empty string if Suggest Proof Using is
unset), there is a key
>context_used "$hyps"
and if Suggest Proof Using is set also a key
>suggest_proof_using "$suggest"

For instance instead of
112 116 context_used "B A;A B;All"
we get
112 116 context_used "B A"
112 116 suggest_proof_using "A B;All"

2 files changed, 38 insertions, 0 deletions

diff --git a/test-suite/output/SuggestProofUsing.out b/test-suite/output/SuggestProofUsing.out
new file mode 100644
index 000000000..97cb0fdd8
--- /dev/null
+++ b/test-suite/output/SuggestProofUsing.out
@@ -0,0 +1,7 @@
+The proof of Top#Sec#nat should start with one of the following commands:
+Proof using . 
+Proof using Type*. 
+Proof using Type. 
+The proof of foo should start with one of the following commands:
+Proof using A B. 
+Proof using All. 
diff --git a/test-suite/output/SuggestProofUsing.v b/test-suite/output/SuggestProofUsing.v
new file mode 100644
index 000000000..b0b514a52
--- /dev/null
+++ b/test-suite/output/SuggestProofUsing.v
@@ -0,0 +1,31 @@
+Set Suggest Proof Using.
+
+Section Sec.
+  Variables A B : Type.
+
+  (* Some normal lemma. Sadly the internal name gets printed. *)
+  Lemma nat : Set.
+  Proof.
+    exact nat.
+  Qed.
+
+  (* Make sure All is suggested even though we add an unused variable
+  to the context. *)
+  Let foo : Type.
+  Proof.
+    exact (A -> B).
+  Qed.
+
+  (* Having a [Proof using] disables the suggestion message. *)
+  Definition bar : Type.
+  Proof using A.
+    exact A.
+  Qed.
+
+  (* Transparent definitions don't get a suggestion message. *)
+  Definition baz : Type.
+  Proof.
+    exact A.
+  Defined.
+
+End Sec.