[Diagnostics] Suppress expression diagnostics for code completion

Any produced diagnostics are suppressed anyway by a special
diagnostic engine attached to the new type-checker, so there
no point of doing any of that work.

Resolves: rdar://problem/22996887

Author: xedin

lib/Sema/CSGen.cpp

@@ -1167,6 +1167,7 @@ namespace {
       if (!E->isActivated())
         return Type();
 
+      CS.Options |= ConstraintSystemFlags::SuppressDiagnostics;
       return CS.createTypeVariable(CS.getConstraintLocator(E),
                                    TVO_CanBindToLValue);
     }
@@ -3562,6 +3563,8 @@ class InferUnresolvedMemberConstraintGenerator : public ConstraintGenerator {
   }
 
   Type visitCodeCompletionExpr(CodeCompletionExpr *Expr) override {
+    auto &cs = getConstraintSystem();
+    cs.Options |= ConstraintSystemFlags::SuppressDiagnostics;
     return createFreeTypeVariableType(Expr);
   }
 

lib/Sema/TypeCheckConstraints.cpp

@@ -2160,7 +2160,7 @@ bool TypeChecker::typeCheckCompletionSequence(Expr *&expr, DeclContext *DC) {
   PrettyStackTraceExpr stackTrace(Context, "type-checking", expr);
 
   // Construct a constraint system from this expression.
-  ConstraintSystem CS(*this, DC, ConstraintSystemFlags::AllowFixes);
+  ConstraintSystem CS(*this, DC, ConstraintSystemFlags::SuppressDiagnostics);
   CleanupIllFormedExpressionRAII cleanup(expr);
 
   auto *SE = cast<SequenceExpr>(expr);

lib/Sema/TypeChecker.cpp

@@ -900,13 +900,17 @@ bool swift::typeCheckExpression(DeclContext *DC, Expr *&parsedExpr) {
   auto &ctx = DC->getASTContext();
   if (ctx.getLazyResolver()) {
     TypeChecker *TC = static_cast<TypeChecker *>(ctx.getLazyResolver());
-    auto resultTy = TC->typeCheckExpression(parsedExpr, DC);
+    auto resultTy = TC->typeCheckExpression(parsedExpr, DC, TypeLoc(),
+                                      ContextualTypePurpose::CTP_Unused,
+                                      TypeCheckExprFlags::SuppressDiagnostics);
     return !resultTy;
   } else {
     // Set up a diagnostics engine that swallows diagnostics.
     DiagnosticEngine diags(ctx.SourceMgr);
     TypeChecker TC(ctx, diags);
-    auto resultTy = TC.typeCheckExpression(parsedExpr, DC);
+    auto resultTy = TC.typeCheckExpression(parsedExpr, DC, TypeLoc(),
+                                      ContextualTypePurpose::CTP_Unused,
+                                      TypeCheckExprFlags::SuppressDiagnostics);
     return !resultTy;
   }
 }

test/IDE/complete_operators.swift

@@ -210,8 +210,6 @@ func testInfix7(x: S2?) {
   x#^INFIX_7^#
 }
 // S2_INFIX_OPTIONAL: Begin completions
-// FIXME: rdar://problem/22996887 - shouldn't complete with optional LHS
-// S2_INFIX_OPTIONAL-DAG: Decl[InfixOperatorFunction]/CurrModule:   ** {#Int#}[#S2#]
 // S2_INFIX_OPTIONAL-DAG: Decl[InfixOperatorFunction]/OtherModule[Swift]:  != {#{{.*}}#}[#Bool#]
 // S2_INFIX_OPTIONAL-DAG: Decl[InfixOperatorFunction]/OtherModule[Swift]:  == {#{{.*}}#}[#Bool#]
 // S2_INFIX_OPTIONAL-DAG: Decl[InfixOperatorFunction]/OtherModule[Swift]:  ?? {#S2#}[#S2#]; name=?? S2