Report a useful error for dependent destruction

Similar to `dependent induction`, report an error message for `dependent
destruction` saying that importing `Coq.Program.Equality` is required,
rather than failing at parsing time.

This is a small extension of #605 to cover dependent destruction as
well. Here I also put in some tests.

2 files changed, 21 insertions, 0 deletions

diff --git a/test-suite/output/DependentInductionErrors.out b/test-suite/output/DependentInductionErrors.out
new file mode 100644
index 0000000000..4a83375f6f
--- /dev/null
+++ b/test-suite/output/DependentInductionErrors.out
@@ -0,0 +1,4 @@
+The command has indeed failed with message:
+Tactic failure: To use dependent destruction, first [Require Import Coq.Program.Equality.].
+The command has indeed failed with message:
+Tactic failure: To use dependent induction, first [Require Import Coq.Program.Equality.].
diff --git a/test-suite/output/DependentInductionErrors.v b/test-suite/output/DependentInductionErrors.v
new file mode 100644
index 0000000000..2fce00f9fd
--- /dev/null
+++ b/test-suite/output/DependentInductionErrors.v
@@ -0,0 +1,17 @@
+Theorem foo (b:bool) : b = true \/ b = false.
+Proof.
+  Fail dependent destruction b.
+  Fail dependent induction b.
+Abort.
+
+From Coq Require Import Program.Equality.
+
+Theorem foo_with_destruction (b:bool) : b = true \/ b = false.
+Proof.
+  dependent destruction b; auto.
+Qed.
+
+Theorem foo_with_induction (b:bool) : b = true \/ b = false.
+Proof.
+  dependent induction b; auto.
+Qed.