fix(library/simplifier): assumptions/context may contain equations where the left-hand-side is a metavariable or semantic attachment

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/library/simplifier/simplifier.cpp

@@ -1465,9 +1465,9 @@ class simplifier_cell::imp {
         switch (e.kind()) {
         case expr_kind::Var:      return result(e);
         case expr_kind::Constant: return save(e, simplify_constant(e));
-        case expr_kind::Type:
+        case expr_kind::Type:     return result(e);
         case expr_kind::MetaVar:
-        case expr_kind::Value:    return result(e);
+        case expr_kind::Value:    return rewrite(e, result(e));
         case expr_kind::App:      return save(e, simplify_app(e));
         case expr_kind::Lambda:   return save(e, simplify_lambda(e));
         case expr_kind::Pi:       return save(e, simplify_pi(e));

tests/lean/simp34.lean

@@ -0,0 +1,6 @@
+import tactic
+
+theorem T : false → false
+:= by simp
+
+print environment

tests/lean/simp34.lean.expected.out

@@ -0,0 +1,7 @@
+  Set: pp::colors
+  Set: pp::unicode
+  Imported 'tactic'
+  Proved: T
+import "kernel"
+import "Nat"
+theorem T (H : ⊥) : ⊥ := eqt_elim (eqt_intro H)