fix lazy vars

clean up lazy vars

more docs

Author: Azoy

lib/AST/Decl.cpp

@@ -5261,7 +5261,7 @@ void DefaultArgumentInitializer::changeFunction(
   }
 
   auto param = paramList->get(getIndex());
-  if (param->isDefaultArgument())
+  if (param->getDefaultValue() || param->getStoredProperty())
     param->setDefaultArgumentInitContext(this);
 }
 

lib/SILGen/SILGenApply.cpp

@@ -3366,7 +3366,7 @@ void DelayedArgument::emitDefaultArgument(SILGenFunction &SGF,
                                                          SGFContext());
       }
     }
-  }                      
+  }
 
   if (!isStoredPropertyDefaultArg) {
     value = SGF.emitApplyOfDefaultArgGenerator(info.loc,

lib/Sema/CodeSynthesis.cpp

@@ -1658,7 +1658,9 @@ static void maybeAddMemberwiseDefaultArg(ParamDecl *arg, VarDecl *var,
   // If we don't have an expression initializer or silgen can't assign a default
   // initializer, then we can't generate a default value. An example of where
   // silgen can assign a default is var x: Int? where the default is nil.
-  if (!var->getParentPatternBinding()->isDefaultInitializable())
+  // If the variable is lazy, go ahead and give it a default value.
+  if (!var->getAttrs().hasAttribute<LazyAttr>() &&
+      !var->getParentPatternBinding()->isDefaultInitializable())
     return;
 
   // We can add a default value now.
@@ -1670,18 +1672,21 @@ static void maybeAddMemberwiseDefaultArg(ParamDecl *arg, VarDecl *var,
 
   defaultInits.push_back(initDC);
 
+  // If the variable has a type T? and no initial value, return a nil literal
+  // default arg. All lazy variables return a nil literal as well. *Note* that
+  // the type will always be a sugared T? because we don't default init an
+  // explicit Optional<T>.
+  if ((isa<OptionalType>(var->getValueInterfaceType().getPointer()) &&
+      !var->getParentInitializer()) ||
+      var->getAttrs().hasAttribute<LazyAttr>()) {
+    arg->setDefaultArgumentKind(DefaultArgumentKind::NilLiteral);
+    return;
+  }
+
   // Set the default value to the variable. When we emit this in silgen
   // we're going to call the variable's initializer expression.
   arg->setStoredProperty(var);
   arg->setDefaultArgumentKind(DefaultArgumentKind::StoredProperty);
-
-  // If the type is T? and has no initial value, then set the default arg kind
-  // to nil literal. This is useful when we need to print the constructor.
-  // Note, this will always be the sugared T? because we don't default init an
-  // explicit Optional<T>.
-  if (isa<OptionalType>(var->getValueInterfaceType().getPointer()) &&
-      !var->getParentInitializer())
-    arg->setDefaultArgumentKind(DefaultArgumentKind::NilLiteral);
 }
 
 /// Create an implicit struct or class constructor.

test/SILGen/stored_property_default_arg.swift

@@ -38,3 +38,24 @@ struct F<T> {
 // CHECK-NEXT: {{.*}} = apply [[F1_REF]]<Int>({{.*}}, {{.*}}, [[H1]], {{.*}}) : $@convention(method) <τ_0_0> (@in τ_0_0, Int, @thin F<τ_0_0>.Type) -> @out F<τ_0_0>
 
 let i = F(g: 128)
+
+struct J {
+  lazy var k: Bool = false
+  lazy var l: Int = 0
+}
+
+// CHECK: {{.*}} = metatype $@thin Optional<Int>.Type
+// CHECK-NEXT: [[L1_REF:%.*]] = enum $Optional<Int>, #Optional.none!enumelt
+// CHECK-NEXT: function_ref J.init(k:l:)
+// CHECK-NEXT: [[J1_REF:%.*]] = function_ref @$s27stored_property_default_arg1JV1k1lACSbSg_SiSgtcfC : $@convention(method) (Optional<Bool>, Optional<Int>, @thin J.Type) -> J
+// CHECK-NEXT: {{.*}} = apply [[J1_REF]]({{.*}}, [[L1_REF]], {{.*}}) : $@convention(method) (Optional<Bool>, Optional<Int>, @thin J.Type) -> J
+
+let m = J(k: true)
+
+// CHECK: {{.*}} = metatype $@thin Optional<Bool>.Type
+// CHECK-NEXT: [[K1_REF:%.*]] = enum $Optional<Bool>, #Optional.none!enumelt
+// CHECK-NEXT: function_ref J.init(k:l:)
+// CHECK-NEXT: [[J2_REF:%.*]] = function_ref @$s27stored_property_default_arg1JV1k1lACSbSg_SiSgtcfC : $@convention(method) (Optional<Bool>, Optional<Int>, @thin J.Type) -> J
+// CHECK-NEXT: {{.*}} = apply [[J2_REF]]([[K1_REF]], {{.*}}, {{.*}}) : $@convention(method) (Optional<Bool>, Optional<Int>, @thin J.Type) -> J
+
+let n = J(l: 316)