Sema: Remove unused -fix-string-to-substring-conversion flag

include/swift/Basic/LangOptions.h

@@ -274,12 +274,6 @@ namespace swift {
     std::shared_ptr<llvm::Regex> OptimizationRemarkPassedPattern;
     std::shared_ptr<llvm::Regex> OptimizationRemarkMissedPattern;
 
-    /// When a conversion from String to Substring fails, emit a fix-it to append
-    /// the void subscript '[]'.
-    /// FIXME: Remove this flag when void subscripts are implemented.
-    /// This is used to guard preemptive testing for the fix-it.
-    bool FixStringToSubstringConversions = false;
-
     /// Whether collect tokens during parsing for syntax coloring.
     bool CollectParsedToken = false;
 

include/swift/Option/FrontendOptions.td

@@ -533,11 +533,6 @@ def validate_tbd_against_ir_EQ: Joined<["-"], "validate-tbd-against-ir=">,
     HelpText<"Compare the symbols in the IR against the TBD file that would be generated.">,
     MetaVarName<"<level>">;
 
-// FIXME: Remove this flag when void subscripts are implemented.
-// This is used to guard preemptive testing for the fix-it.
-def fix_string_substring_conversion: Flag<["-"], "fix-string-substring-conversion">,
-    HelpText<"Emit a fix-it to append '[]' to String expressions when converting to Substring.">;
-
 def bypass_batch_mode_checks: Flag<["-"], "bypass-batch-mode-checks">,
     HelpText<"Bypass checks for batch-mode errors.">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -201,12 +201,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                           const FrontendOptions &FrontendOpts) {
   using namespace options;
 
-  /// FIXME: Remove this flag when void subscripts are implemented.
-  /// This is used to guard preemptive testing for the fix-it.
-  if (Args.hasArg(OPT_fix_string_substring_conversion)) {
-    Opts.FixStringToSubstringConversions = true;
-  }
-
   if (auto A = Args.getLastArg(OPT_swift_version)) {
     auto vers = version::Version::parseVersionString(
       A->getValue(), SourceLoc(), &Diags);

lib/Sema/CSDiagnostics.cpp

@@ -1364,19 +1364,6 @@ bool ContextualFailure::trySequenceSubsequenceFixIts(InFlightDiagnostic &diag,
   if (!String || !Substring)
     return false;
 
-  /// FIXME: Remove this flag when void subscripts are implemented.
-  /// Make this unconditional and remove the if statement.
-  if (CS.TC.getLangOpts().FixStringToSubstringConversions) {
-    // String -> Substring conversion
-    // Add '[]' void subscript call to turn the whole String into a Substring
-    if (fromType->isEqual(String)) {
-      if (toType->isEqual(Substring)) {
-        diag.fixItInsertAfter(expr->getEndLoc(), "[]");
-        return true;
-      }
-    }
-  }
-
   // Substring -> String conversion
   // Wrap in String.init
   if (fromType->isEqual(Substring)) {