Provide a frontend option to disable typo correction.

rdar://29003217

include/swift/Basic/LangOptions.h

@@ -48,6 +48,9 @@ namespace swift {
     /// \brief Disable API availability checking.
     bool DisableAvailabilityChecking = false;
 
+    /// \brief Disable typo correction.
+    bool DisableTypoCorrection = false;
+    
     /// Should access control be respected?
     bool EnableAccessControl = true;
 

include/swift/Option/FrontendOptions.td

@@ -116,6 +116,9 @@ def serialize_debugging_options : Flag<["-"], "serialize-debugging-options">,
 def autolink_library : Separate<["-"], "autolink-library">,
   HelpText<"Add dependent library">, Flags<[FrontendOption]>;
 
+def disable_typo_correction : Flag<["-"], "disable-typo-correction">,
+  HelpText<"Disable typo correction">;
+
 } // end let Flags = [FrontendOption, NoDriverOption]
 
 def debug_crash_Group : OptionGroup<"<automatic crashing options>">;

lib/Frontend/CompilerInvocation.cpp

@@ -821,6 +821,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       = A->getOption().matches(OPT_enable_access_control);
   }
 
+  Opts.DisableTypoCorrection |= Args.hasArg(OPT_disable_typo_correction);
+
   Opts.CodeCompleteInitsInPostfixExpr |=
       Args.hasArg(OPT_code_complete_inits_in_postfix_expr);
 

lib/Sema/TypeCheckNameLookup.cpp

@@ -504,6 +504,9 @@ void TypeChecker::performTypoCorrection(DeclContext *DC, DeclRefKind refKind,
                                         NameLookupOptions lookupOptions,
                                         LookupResult &result,
                                         unsigned maxResults) {
+  if (getLangOpts().DisableTypoCorrection)
+    return;
+
   // Fill in a collection of the most reasonable entries.
   TopCollection<unsigned, ValueDecl*> entries(maxResults);
   auto consumer = makeDeclConsumer([&](ValueDecl *decl,