[IDE] Don't walk into closures in ThrowingEntityAnalyzer

We don't want to consider any `try` exprs here.

Author: hamishknight

lib/IDE/IDERequests.cpp

@@ -393,6 +393,10 @@ static bool hasUnhandledError(ArrayRef<ASTNode> Nodes) {
       return !Throwing;
     }
     bool walkToExprPre(Expr *E) override {
+      // Don't walk into closures, they only produce effects when called.
+      if (isa<ClosureExpr>(E))
+        return false;
+      
       if (isa<TryExpr>(E)) {
         Throwing = true;
       }

test/refactoring/ExtractFunction/Outputs/throw_errors3/consumes_err.swift.expected

@@ -0,0 +1,18 @@
+enum Err : Error {
+  case wat
+}
+
+func throwsSomething() throws { throw Err.wat }
+func consumesErrClosure(_ fn: () throws -> Void) {}
+func rethrowsErrClosure(_ fn: () throws -> Void) rethrows {}
+
+fileprivate func new_name() {
+consumesErrClosure { throw Err.wat }
+  consumesErrClosure { try throwsSomething() }
+}
+
+func testThrowingClosure() throws {
+  new_name()
+  try rethrowsErrClosure { try throwsSomething() }
+}
+

test/refactoring/ExtractFunction/Outputs/throw_errors3/rethrows_err.swift.expected

@@ -0,0 +1,18 @@
+enum Err : Error {
+  case wat
+}
+
+func throwsSomething() throws { throw Err.wat }
+func consumesErrClosure(_ fn: () throws -> Void) {}
+func rethrowsErrClosure(_ fn: () throws -> Void) rethrows {}
+
+fileprivate func new_name() throws {
+consumesErrClosure { throw Err.wat }
+  consumesErrClosure { try throwsSomething() }
+  try rethrowsErrClosure { try throwsSomething() }
+}
+
+func testThrowingClosure() throws {
+  try new_name()
+}
+

test/refactoring/ExtractFunction/throw_errors3.swift

@@ -0,0 +1,19 @@
+enum Err : Error {
+  case wat
+}
+
+func throwsSomething() throws { throw Err.wat }
+func consumesErrClosure(_ fn: () throws -> Void) {}
+func rethrowsErrClosure(_ fn: () throws -> Void) rethrows {}
+
+func testThrowingClosure() throws {
+  consumesErrClosure { throw Err.wat }
+  consumesErrClosure { try throwsSomething() }
+  try rethrowsErrClosure { try throwsSomething() }
+}
+
+// RUN: %empty-directory(%t.result)
+// RUN: %refactor -extract-function -source-filename %s -pos=10:1 -end-pos=11:47 >> %t.result/consumes_err.swift
+// RUN: diff -u %S/Outputs/throw_errors3/consumes_err.swift.expected %t.result/consumes_err.swift
+// RUN: %refactor -extract-function -source-filename %s -pos=10:1 -end-pos=12:51 >> %t.result/rethrows_err.swift
+// RUN: diff -u %S/Outputs/throw_errors3/rethrows_err.swift.expected %t.result/rethrows_err.swift