Rename tuple fields after discriminant is removed

When the discriminant is removed from an enum's members, be sure to
rename the fields of any tuple type.  This fixes a bug introduced in
yesterday's patch.

Author: tromey

lldb/packages/Python/lldbsuite/test/lang/rust/expressions/TestRustExpressions.py

@@ -119,11 +119,9 @@ def rust_expressions(self):
         v = frame.EvaluateExpression("*vu8ref")
         self.assertEqual("(u8) *vu8ref = 23", str(v))
         v = frame.EvaluateExpression("vsimpleenum", lldb.eDynamicDontRunTarget)
-        # Note that this relies on the pre-DW_TAG_variant rustc.
-        self.assertEqual("(main::SimpleEnum::Two) vsimpleenum = (1 = 83, 2 = 92)", str(v))
+        self.assertEqual("(main::SimpleEnum::Two) vsimpleenum = (0 = 83, 1 = 92)", str(v))
         v = frame.EvaluateExpression("vsimpleenum.1")
-        # Note that this relies on the pre-DW_TAG_variant rustc.
-        self.assertEqual("(u16) 2 = 92", str(v))
+        self.assertEqual("(u16) 1 = 92", str(v))
         v = frame.EvaluateExpression("vsimpleenum1.f2")
         self.assertEqual("(u8) f2 = 83", str(v))
         v = frame.EvaluateExpression("vi8 = 7")

lldb/packages/Python/lldbsuite/test/lang/rust/types/TestRustASTContext.py

@@ -159,8 +159,7 @@ def check_structs(self):
     def check_enums(self):
         address_size = self.target().GetAddressByteSize()
         mytypelist = []
-        # Note that this relies on the pre-DW_TAG_variant rustc.
-        mytypelist.append(('main::SimpleEnum::Two', 'vsimpleenum', 6, '(1 = 83, 2 = 92)'))
+        mytypelist.append(('main::SimpleEnum::Two', 'vsimpleenum', 6, '(0 = 83, 1 = 92)'))
         mytypelist.append(('main::OptimizedEnum::Null', 'voptenum', address_size, '{}'))
         mytypelist.append(('main::OptimizedEnum::NonNull', 'voptenum2', address_size, None))
         for (name, vname, size, value) in mytypelist:

lldb/source/Symbol/RustASTContext.cpp

@@ -410,7 +410,7 @@ class RustAggregateBase : public RustType {
   // With the old-style enum encoding, after the discriminant's
   // location is computed the member types no longer need to have
   // theirs, so they are dropped.
-  void DropDiscriminant() {
+  virtual void DropDiscriminant() {
     if (m_has_discriminant) {
       m_has_discriminant = false;
       m_fields.erase(m_fields.begin());
@@ -461,6 +461,12 @@ class RustAggregateBase : public RustType {
     return result;
   }
 
+  Field *MutableFieldAt(size_t idx) {
+    if (idx >= m_fields.size())
+      return nullptr;
+    return &m_fields[idx];
+  }
+
 private:
 
   uint64_t m_byte_size;
@@ -509,6 +515,17 @@ class RustTuple : public RustAggregateBase {
     return tagname + " " + varname;
   }
 
+  void DropDiscriminant() override {
+    RustAggregateBase::DropDiscriminant();
+    // Rename the fields, because we dropped the first one.
+    for (size_t i = 0; i < FieldCount(); ++i) {
+      Field *f = MutableFieldAt(i);
+      char buf[32];
+      snprintf (buf, sizeof (buf), "%u", unsigned(i));
+      f->m_name = ConstString(buf);
+    }
+  }
+
 private:
 
   // As opposed to a tuple struct.