[Sema] Assert we don't type-check bindings independently of closures

Bindings in closures must be type-checked together with the surrounding
closure, add an assertion to make sure we don't try this. Carve out
an exception for code completion which may still kick lazy
type-checking on failure.

Author: hamishknight

lib/Sema/TypeCheckConstraints.cpp

@@ -841,6 +841,22 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
                 initializer, DC, patternType, pattern,
                 /*bindPatternVarsOneWay=*/false);
 
+  // Bindings cannot be type-checked independently from their context in a
+  // closure, make sure we don't ever attempt to do this. If we want to be able
+  // to lazily type-check these we'll need to type-check the entire surrounding
+  // expression.
+  if (auto *CE = dyn_cast<ClosureExpr>(DC)) {
+    if (!PBD || !isPlaceholderVar(PBD)) {
+      // Completion may trigger lazy type-checking as part of fallback
+      // unqualified lookup, just decline to type-check.
+      if (CE->getASTContext().SourceMgr.hasIDEInspectionTargetBuffer()) {
+        target.markInvalid();
+        return true;
+      }
+      ABORT("Cannot type-check PatternBindingDecl without closure context");
+    }
+  }
+
   // Type-check the initializer.
   auto resultTarget = typeCheckExpression(target, options);
 

test/IDE/complete_unqualified_fallback.swift

@@ -1,4 +1,4 @@
-// RUN: %batch-code-completion
+// RUN: %batch-code-completion -solver-scope-threshold=50
 
 protocol P0 {}
 protocol P1 {}
@@ -47,8 +47,14 @@ S {
     S {
       S {
         S {
+          let x = 0
           #^COMPLETE^#
-          // COMPLETE: Decl[Struct]/CurrModule: FooBar[#FooBar#]; name=FooBar
+          // COMPLETE-DAG: Decl[Struct]/CurrModule: FooBar[#FooBar#]; name=FooBar
+
+          // We decline to type-check a variable indepedently of the surrounding
+          // closure, so this has an ErrorType. If this changes, you either need
+          // to make this test case more complex or tweak the limits.
+          // COMPLETE-DAG: Decl[LocalVar]/Local: x[#_#]; name=x
         }
       }
     }

validation-test/compiler_crashers_fixed/TypeChecker-typeCheckBinding-adf55f.swift

@@ -0,0 +1,7 @@
+// {"kind":"typecheck","original":"22c204bc","signature":"swift::TypeChecker::typeCheckBinding(swift::Pattern*&, swift::Expr*&, swift::DeclContext*, swift::Type, swift::PatternBindingDecl*, unsigned int, swift::optionset::OptionSet<swift::TypeCheckExprFlags, unsigned int>)"}
+// RUN: not %target-swift-frontend -typecheck %s
+struct a: ExpressibleByIntegerLiteral
+  func *** (a , a )
+}
+{
+  let b = 3 *** 4