[CodeCompletion] Fix an issue that caused us to not produce any results for a guard condition inside a closure

lib/Sema/CSBindings.cpp

@@ -2522,6 +2522,17 @@ TypeVariableBinding::fixForHole(ConstraintSystem &cs) const {
                        FixKind::IgnoreCollectionElementContextualMismatch)) {
         return llvm::None;
       }
+      if (dstLocator->getAnchor().isExpr(ExprKind::CodeCompletion)) {
+        // Ignore the hole if it is because the right-hand-side of the pattern
+        // match is a code completion token. Assigning a high fix score to this
+        // mismatch won't help. In fact, it can harm because we might have a
+        // different exploration path in the constraint system that gives up
+        // earlier (eg. because code completion is in a closure that doesn't
+        // match the expected parameter of a function call) and might thus get a
+        // better score, despite not having any information about the code
+        // completion token at all.
+        return llvm::None;
+      }
       // Not being able to infer the type of a variable in a pattern binding
       // decl is more dramatic than anything that could happen inside the
       // expression because we want to preferrably point the diagnostic to a

test/IDE/complete_pattern_match_in_closure.swift

@@ -0,0 +1,14 @@
+// RUN: %batch-code-completion
+
+func run(execute workItem: Int) {}
+func run(execute work: () -> Void) {}
+
+func test(myVar: Int) {
+  run {
+    guard let data = #^COMPLETE^# else {
+      return
+    }
+  }
+}
+
+// COMPLETE: Decl[LocalVar]/Local:               myVar[#Int#]; name=myVar