[Parse][Swift3] Add a warning for unsupported conditional compiliation expression

Author: rintaro

include/swift/AST/DiagnosticsParse.def

@@ -1356,6 +1356,9 @@ ERROR(unexpected_version_comparison_operator,none,
       ())
 ERROR(unsupported_conditional_compilation_expression_type,none,
       "invalid conditional compilation expression", ())
+WARNING(swift3_unsupported_conditional_compilation_expression_type,none,
+        "ignoring invalid conditional compilation expression, "
+        "which will be rejected in future version of Swift", ())
 ERROR(unsupported_conditional_compilation_integer,none,
       "'%0' is not a valid conditional compilation expression, use '%1'",
       (StringRef, StringRef))

lib/Parse/ParseStmt.cpp

@@ -1584,7 +1584,12 @@ Parser::classifyConditionalCompilationExpr(Expr *condition,
               diag::unsupported_conditional_compilation_expression_type);
           return ConditionalCompilationExprState::error();
         } else {
-          // TODO: Emit a warning.
+          SourceRange ignoredRange(elements[iOperator]->getLoc(),
+                                   elements[iOperand]->getEndLoc());
+          D.diagnose(
+              elements[iOperator]->getLoc(),
+              diag::swift3_unsupported_conditional_compilation_expression_type)
+            .highlight(ignoredRange);
         }
       }
 

test/Compatibility/conditional_compiliation_expr.swift

@@ -2,6 +2,7 @@
 
 
 #if FOO = false
+// expected-warning @-1 {{ignoring invalid conditional compilation expression, which will be rejected in future version of Swift}}
 undefinedFunc() // expected-error {{use of unresolved identifier 'undefinedFunc'}}
 #else
 undefinedFunc() // ignored.
@@ -10,6 +11,7 @@ undefinedFunc() // ignored.
 #if false
 
 #elseif !FOO ? false : true
+// expected-warning @-1 {{ignoring invalid conditional compilation expression, which will be rejected in future version of Swift}}
 undefinedFunc() // ignored.
 #else
 undefinedFunc() // expected-error {{use of unresolved identifier 'undefinedFunc'}}