Update comments

Author: nickolas-pohilets

include/swift/AST/Stmt.h

@@ -727,8 +727,6 @@ class alignas(1 << PatternAlignInBits) StmtConditionElement {
   /// or `let self = self` condition.
   ///  - If `requiresCaptureListRef` is `true`, additionally requires that the
   ///    RHS of the self condition references a var defined in a capture list.
-  ///  - If `requireLoadExpr` is `true`, additionally requires that the RHS of
-  ///    the self condition is a `LoadExpr`.
   bool rebindsSelf(ASTContext &Ctx, bool requiresCaptureListRef = false) const;
 
   SourceLoc getStartLoc() const;
@@ -838,8 +836,6 @@ class LabeledConditionalStmt : public LabeledStmt {
   /// or `let self = self` condition.
   ///  - If `requiresCaptureListRef` is `true`, additionally requires that the
   ///    RHS of the self condition references a var defined in a capture list.
-  ///  - If `requireLoadExpr` is `true`, additionally requires that the RHS of
-  ///    the self condition is a `LoadExpr`.
   bool rebindsSelf(ASTContext &Ctx, bool requiresCaptureListRef = false) const;
 
   static bool classof(const Stmt *S) {

lib/AST/Stmt.cpp

@@ -514,8 +514,6 @@ void LabeledConditionalStmt::setCond(StmtCondition e) {
 /// or `let self = self` condition.
 ///  - If `requiresCaptureListRef` is `true`, additionally requires that the
 ///    RHS of the self condition references a var defined in a capture list.
-///  - If `requireLoadExpr` is `true`, additionally requires that the RHS of
-///    the self condition is a `LoadExpr`.
 bool LabeledConditionalStmt::rebindsSelf(ASTContext &Ctx,
                                          bool requiresCaptureListRef) const {
   return llvm::any_of(getCond(), [&Ctx, requiresCaptureListRef](const auto &cond) {
@@ -527,8 +525,6 @@ bool LabeledConditionalStmt::rebindsSelf(ASTContext &Ctx,
 /// or `let self = self` condition.
 ///  - If `requiresCaptureListRef` is `true`, additionally requires that the
 ///    RHS of the self condition references a var defined in a capture list.
-///  - If `requireLoadExpr` is `true`, additionally requires that the RHS of
-///    the self condition is a `LoadExpr`.
 bool StmtConditionElement::rebindsSelf(ASTContext &Ctx,
                                        bool requiresCaptureListRef) const {
   auto pattern = getPatternOrNull();

lib/Sema/MiscDiagnostics.cpp

@@ -1748,13 +1748,22 @@ class ImplicitSelfUsageChecker : public BaseDiagnosticWalker {
       return false;
     }
 
-    // Require `LoadExpr`s when validating the self binding.
+    // Require that the RHS of the `let self = self` condition
+    // refers to a variable defined in a capture list.
     // This lets us reject invalid examples like:
     //
-    //   let `self` = self ?? .somethingElse
+    //   var `self` = self ?? .somethingElse
     //   guard let self = self else { return }
     //   method() // <- implicit self is not allowed
     //
+    // In 5.10, instead of this check, compiler was checking that RHS of the
+    // self binding is loaded from a mutable variable. This is incorrect, but
+    // before SE-0481 compiler was trying to maintain this behavior in Swift 5
+    // mode for source compatibility. After SE-0481 this does not work
+    // anymore, because even in Swift 5 mode `weak self` capture is not mutable.
+    // So we have to introduce a breaking change as part of the SE-0481, and use
+    // proper check for capture list even in Swift 5 mode.
+    //
     return conditionalStmt->rebindsSelf(Ctx, /*requiresCaptureListRef*/ true);
   }