Merge pull request #17622 from DougGregor/fix-optional-rethrows-checking

[Type checker] Look through optionals when checking for rethrows.

Author: DougGregor

lib/Sema/TypeCheckError.cpp

@@ -134,6 +134,9 @@ class AbstractFunction {
         fn = conversion->getSubExpr()->getValueProvidingExpr();
       } else if (auto conversion = dyn_cast<BindOptionalExpr>(fn)) {
         fn = conversion->getSubExpr()->getValueProvidingExpr();
+      // Look through optional injections
+      } else if (auto injection = dyn_cast<InjectIntoOptionalExpr>(fn)) {
+        fn = injection->getSubExpr()->getValueProvidingExpr();
       // Look through function conversions.
       } else if (auto conversion = dyn_cast<FunctionConversionExpr>(fn)) {
         fn = conversion->getSubExpr()->getValueProvidingExpr();

validation-test/compiler_crashers_2_fixed/0165-sr5427.swift

@@ -0,0 +1,7 @@
+// RUN: %target-typecheck-verify-swift
+
+// Used to crash with: apply expression is not marked as throwing or
+// non-throwing
+struct SR5427 : Error {}
+func sr5427(op: (() throws -> Void)?) rethrows { try op?() }
+try? sr5427(op: { throw SR5427() })