Sema: Remove a usage of hasComputedGenericSignature() from expression checker diagnostics

Removing this exposed a re-entrant diagnostic emission, so let's fix that too.

Author: slavapestov

lib/Sema/MiscDiagnostics.cpp

@@ -1840,13 +1840,9 @@ bool TypeChecker::getDefaultGenericArgumentsString(
     genericParamText << contextTy;
   };
 
-  // FIXME: We can potentially be in the middle of creating a generic signature
-  // if we get here.  Break this cycle.
-  if (typeDecl->hasComputedGenericSignature()) {
-    llvm::interleave(typeDecl->getInnermostGenericParamTypes(),
-                     printGenericParamSummary,
-                     [&] { genericParamText << ", "; });
-  }
+  llvm::interleave(typeDecl->getInnermostGenericParamTypes(),
+                   printGenericParamSummary,
+                   [&] { genericParamText << ", "; });
 
   genericParamText << ">";
   return true;

lib/Sema/TypeCheckType.cpp

@@ -996,11 +996,17 @@ static void diagnoseUnboundGenericType(Type ty, SourceLoc loc) {
   if (auto unbound = ty->getAs<UnboundGenericType>()) {
     auto *decl = unbound->getDecl();
     {
-      InFlightDiagnostic diag = ctx.Diags.diagnose(loc,
-          diag::generic_type_requires_arguments, ty);
+      // Compute the string before creating a new diagnostic, since
+      // getDefaultGenericArgumentsString() might emit its own
+      // diagnostics.
       SmallString<64> genericArgsToAdd;
-      if (TypeChecker::getDefaultGenericArgumentsString(genericArgsToAdd,
-                                                        decl))
+      bool hasGenericArgsToAdd =
+          TypeChecker::getDefaultGenericArgumentsString(genericArgsToAdd,
+                                                        decl);
+
+      auto diag = ctx.Diags.diagnose(loc,
+          diag::generic_type_requires_arguments, ty);
+      if (hasGenericArgsToAdd)
         diag.fixItInsertAfter(loc, genericArgsToAdd);
     }