Fix init-captures for generic lambdas.

For an init capture, process the initialization expression
right away.  For lambda init-captures such as the following:
const int x = 10;
 auto L = [i = x+1](int a) {
   return [j = x+2,
          &k = x](char b) { };
 };
keep in mind that each lambda init-capture has to have:
 - its initialization expression executed in the context
   of the enclosing/parent decl-context.
 - but the variable itself has to be 'injected' into the
   decl-context of its lambda's call-operator (which has
   not yet been created).
Each init-expression is a full-expression that has to get
Sema-analyzed (for capturing etc.) before its lambda's
call-operator's decl-context, scope & scopeinfo are pushed on their
respective stacks.  Thus if any variable is odr-used in the init-capture
it will correctly get captured in the enclosing lambda, if one exists.
The init-variables above are created later once the lambdascope and
call-operators decl-context is pushed onto its respective stack.

Since the lambda init-capture's initializer expression occurs in the
context of the enclosing function or lambda, therefore we can not wait
till a lambda scope has been pushed on before deciding whether the
variable needs to be captured.  We also need to process all
lvalue-to-rvalue conversions and discarded-value conversions,
so that we can avoid capturing certain constant variables.
For e.g.,
 void test() {
  const int x = 10;
  auto L = [&z = x](char a) { <-- don't capture by the current lambda
    return [y = x](int i) { <-- don't capture by enclosing lambda
         return y;
    }
  };
If x was not const, the second use would require 'L' to capture, and
that would be an error.
Make sure TranformLambdaExpr is also aware of this.

Patch approved by Richard (Thanks!!) 
http://llvm-reviews.chandlerc.com/D2092

llvm-svn: 196454

1 files changed, 59 insertions, 6 deletions

diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 9489b4787e2..3f6d36c8b8d 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -637,8 +637,7 @@ ExprResult Parser::ParseCXXIdExpression(bool isAddressOfOperand) {
 ExprResult Parser::ParseLambdaExpression() {
   // Parse lambda-introducer.
   LambdaIntroducer Intro;
-
-  Optional<unsigned> DiagID(ParseLambdaIntroducer(Intro));
+  Optional<unsigned> DiagID = ParseLambdaIntroducer(Intro);
   if (DiagID) {
     Diag(Tok, DiagID.getValue());
     SkipUntil(tok::r_square, StopAtSemi);
@@ -678,7 +677,7 @@ ExprResult Parser::TryParseLambdaExpression() {
   if (Next.is(tok::identifier) && After.is(tok::identifier)) {
     return ExprEmpty();
   }
-
+ 
   // Here, we're stuck: lambda introducers and Objective-C message sends are
   // unambiguous, but it requires arbitrary lookhead.  [a,b,c,d,e,f,g] is a
   // lambda, and [a,b,c,d,e,f,g h] is a Objective-C message send.  Instead of
@@ -688,6 +687,7 @@ ExprResult Parser::TryParseLambdaExpression() {
   LambdaIntroducer Intro;
   if (TryParseLambdaIntroducer(Intro))
     return ExprEmpty();
+
   return ParseLambdaExpressionAfterIntroducer(Intro);
 }
 
@@ -813,6 +813,11 @@ Optional<unsigned> Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
                                             Exprs);
         }
       } else if (Tok.is(tok::l_brace) || Tok.is(tok::equal)) {
+        // Each lambda init-capture forms its own full expression, which clears
+        // Actions.MaybeODRUseExprs. So create an expression evaluation context
+        // to save the necessary state, and restore it later.
+        EnterExpressionEvaluationContext EC(Actions,
+                                            Sema::PotentiallyEvaluated);
         if (Tok.is(tok::equal))
           ConsumeToken();
 
@@ -866,13 +871,61 @@ Optional<unsigned> Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
       } else if (Tok.is(tok::ellipsis))
         EllipsisLoc = ConsumeToken();
     }
-
-    Intro.addCapture(Kind, Loc, Id, EllipsisLoc, Init);
+    // If this is an init capture, process the initialization expression
+    // right away.  For lambda init-captures such as the following:
+    // const int x = 10;
+    //  auto L = [i = x+1](int a) {
+    //    return [j = x+2,
+    //           &k = x](char b) { };
+    //  };
+    // keep in mind that each lambda init-capture has to have:
+    //  - its initialization expression executed in the context
+    //    of the enclosing/parent decl-context.
+    //  - but the variable itself has to be 'injected' into the
+    //    decl-context of its lambda's call-operator (which has
+    //    not yet been created).
+    // Each init-expression is a full-expression that has to get
+    // Sema-analyzed (for capturing etc.) before its lambda's
+    // call-operator's decl-context, scope & scopeinfo are pushed on their
+    // respective stacks.  Thus if any variable is odr-used in the init-capture
+    // it will correctly get captured in the enclosing lambda, if one exists.
+    // The init-variables above are created later once the lambdascope and
+    // call-operators decl-context is pushed onto its respective stack.
+
+    // Since the lambda init-capture's initializer expression occurs in the
+    // context of the enclosing function or lambda, therefore we can not wait
+    // till a lambda scope has been pushed on before deciding whether the
+    // variable needs to be captured.  We also need to process all
+    // lvalue-to-rvalue conversions and discarded-value conversions,
+    // so that we can avoid capturing certain constant variables.
+    // For e.g.,
+    //  void test() {
+    //   const int x = 10;
+    //   auto L = [&z = x](char a) { <-- don't capture by the current lambda
+    //     return [y = x](int i) { <-- don't capture by enclosing lambda
+    //          return y;
+    //     }
+    //   };
+    // If x was not const, the second use would require 'L' to capture, and
+    // that would be an error.
+
+    ParsedType InitCaptureParsedType;
+    if (Init.isUsable()) {
+      // Get the pointer and store it in an lvalue, so we can use it as an
+      // out argument.
+      Expr *InitExpr = Init.get();
+      // This performs any lvalue-to-rvalue conversions if necessary, which
+      // can affect what gets captured in the containing decl-context.
+      QualType InitCaptureType = Actions.performLambdaInitCaptureInitialization(
+        Loc, Kind == LCK_ByRef, Id, InitExpr);
+      Init = InitExpr;
+      InitCaptureParsedType.set(InitCaptureType);
+    }
+    Intro.addCapture(Kind, Loc, Id, EllipsisLoc, Init, InitCaptureParsedType);
   }
 
   T.consumeClose();
   Intro.Range.setEnd(T.getCloseLocation());
-
   return DiagResult();
 }