Merge pull request #15559 from xedin/rdar-38144674

[Sema] Fix `PreCheckExpression` to avoid walking into capture lists

Author: xedin

lib/Sema/TypeCheckConstraints.cpp

@@ -824,7 +824,12 @@ namespace {
           TC.typeCheckDecl(capture.Var, true);
           TC.typeCheckDecl(capture.Var, false);
         }
-        return finish(true, expr);
+
+        // Since closure expression is contained by capture list
+        // let's handle it directly to avoid walking into capture
+        // list itself.
+        captureList->getClosureBody()->walk(*this);
+        return finish(false, expr);
       }
 
       // For closures, type-check the patterns and result type as written,

validation-test/compiler_crashers_2_fixed/0149-rdar34852808.swift

@@ -0,0 +1,12 @@
+// RUN: %target-typecheck-verify-swift %s
+
+func foo(optional: Int?) {
+  _ = { [value = optional ?? 0]
+    in
+    _ = value
+  }
+
+  _ = [1].map { [number = optional ?? 1] value -> String in
+    return number.description
+  }
+}