[Effects handling] Move "illegal context" strings into diagnostic text.

The "illegal context" diagnostics were passing strings from the C++
code directly into diagnostic text for things like "a default
argument". That causes a bunch of duplicated code and defeats
localization of diagnostics, so move to a %select in the diagnostic.

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -4008,10 +4008,13 @@ ERROR(throw_in_nonexhaustive_catch,none,
       "error is not handled because the enclosing catch is not exhaustive", ())
 
 ERROR(throwing_call_in_illegal_context,none,
-      "call can throw, but errors cannot be thrown out of %0",
-      (StringRef))
+      "call can throw, but errors cannot be thrown out of "
+      "%select{<<ERROR>>|a default argument|a property initializer|a global variable initializer|an enum case raw value|a catch pattern|a catch guard expression|a defer body}0",
+      (unsigned))
 ERROR(throw_in_illegal_context,none,
-      "errors cannot be thrown out of %0", (StringRef))
+      "errors cannot be thrown out of "
+      "%select{<<ERROR>>|a default argument|a property initializer|a global variable initializer|an enum case raw value|a catch pattern|a catch guard expression|a defer body}0",
+      (unsigned))
 
 ERROR(throwing_operator_without_try,none,
       "operator can throw but expression is not marked with 'try'", ())

lib/Sema/TypeCheckEffects.cpp

@@ -1030,17 +1030,17 @@ class Context {
 
   static void diagnoseThrowInIllegalContext(DiagnosticEngine &Diags,
                                             ASTNode node,
-                                            StringRef description) {
+                                            Kind kind) {
     if (auto *e = node.dyn_cast<Expr*>()) {
       if (isa<ApplyExpr>(e)) {
         Diags.diagnose(e->getLoc(), diag::throwing_call_in_illegal_context,
-                       description);
+                       static_cast<unsigned>(kind));
         return;
       }
     }
 
     Diags.diagnose(node.getStartLoc(), diag::throw_in_illegal_context,
-                   description);
+                   static_cast<unsigned>(kind));
   }
 
   static void maybeAddRethrowsNote(DiagnosticEngine &Diags, SourceLoc loc,
@@ -1174,31 +1174,15 @@ class Context {
       return;
 
     case Kind::EnumElementInitializer:
-      diagnoseThrowInIllegalContext(Diags, E, "an enum case raw value");
-      return;
-
     case Kind::GlobalVarInitializer:
-      diagnoseThrowInIllegalContext(Diags, E, "a global variable initializer");
-      return;
-
     case Kind::IVarInitializer:
-      diagnoseThrowInIllegalContext(Diags, E, "a property initializer");
-      return;
-
     case Kind::DefaultArgument:
-      diagnoseThrowInIllegalContext(Diags, E, "a default argument");
-      return;
-
     case Kind::CatchPattern:
-      diagnoseThrowInIllegalContext(Diags, E, "a catch pattern");
-      return;
-
     case Kind::CatchGuard:
-      diagnoseThrowInIllegalContext(Diags, E, "a catch guard expression");
-      return;
     case Kind::DeferBody:
-      diagnoseThrowInIllegalContext(Diags, E, "a defer body");
+      diagnoseThrowInIllegalContext(Diags, E, getKind());
       return;
+
     }
     llvm_unreachable("bad context kind");
   }