[ConstraintSystem] Ignore patterns in linked expression analysis (#18487)

Fixes an assertion hit in "pattern in binary expression" case.

rdar://problem/41071587

Author: rintaro

lib/Sema/CSGen.cpp

@@ -177,6 +177,14 @@ namespace {
 
     /// \brief Ignore declarations.
     bool walkToDeclPre(Decl *decl) override { return false; }
+
+    /// \brief Ignore patterns.
+    std::pair<bool, Pattern*> walkToPatternPre(Pattern *pat) override {
+      return { false, pat };
+    }
+
+    /// \brief Ignore types.
+    bool walkToTypeLocPre(TypeLoc &TL) override { return false; }
   };
 
   /// Given a collection of "linked" expressions, analyzes them for
@@ -338,6 +346,14 @@ namespace {
 
     /// \brief Ignore declarations.
     bool walkToDeclPre(Decl *decl) override { return false; }
+
+    /// \brief Ignore patterns.
+    std::pair<bool, Pattern*> walkToPatternPre(Pattern *pat) override {
+      return { false, pat };
+    }
+
+    /// \brief Ignore types.
+    bool walkToTypeLocPre(TypeLoc &TL) override { return false; }
   };
 
   /// For a given expression, given information that is global to the

test/IDE/complete_crashes.swift

@@ -357,3 +357,13 @@ extension Foo {
 // RDAR_41234606-DAG: Decl[AssociatedType]/Super:         .Element; name=Element
 // RDAR_41234606-DAG: Decl[AssociatedType]/Super:         .Iterator; name=Iterator
 // RDAR_41234606: End completions
+
+// rdar://problem/41071587
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=RDAR_41071587 -source-filename=%s | %FileCheck %s -check-prefix=RDAR_41071587
+func test_41071587(x: Any) {
+  switch x {
+    case (let (_, _)) #^RDAR_41071587^#:
+      ()
+  }
+}
+// RDAR_41071587: Begin completions

test/Parse/matching_patterns.swift

@@ -286,6 +286,10 @@ case (_, var e, 3) +++ (1, 2, 3):
 // expected-error@-1{{'_' can only appear in a pattern}}
 // expected-error@-2{{'var' binding pattern cannot appear in an expression}}
   ()
+case (let (_, _, _)) + 1:
+// expected-error@-1 2 {{'var' binding pattern cannot appear in an expression}}
+// expected-error@-2 {{expression pattern of type 'Int' cannot match values of type '(Int, Int, Int)'}}
+  ()
 }
 
 // FIXME: We don't currently allow subpatterns for "isa" patterns that