[Parse] Minor improvements in conditional compilation block parsing

* Don't emit duplicated 'expected #else or #endif at end of conditional
  compilation block' error.

    class Foo {
      #if true
        func foo() {}
    [EOF]

* Improve error message when seeing '}' in config block.

    class Foo {
    #if true
        func foo();
    } // error: unexpected '}' in conditional compilation block
    #else
    #endif

Author: rintaro

include/swift/AST/DiagnosticsParse.def

@@ -65,6 +65,8 @@ ERROR(incomplete_conditional_compilation_directive,none,
       "incomplete condition in conditional compilation directive", ())
 ERROR(extra_tokens_conditional_compilation_directive,none,
       "extra tokens following conditional compilation directive", ())
+ERROR(unexpected_rbrace_in_conditional_compilation_block,none,
+      "unexpected '}' in conditional compilation block", ())
 
 ERROR(sourceLocation_expected,none,
       "expected '%0' in #sourceLocation directive", (StringRef))

lib/Parse/ParseDecl.cpp

@@ -3045,19 +3045,18 @@ ParserResult<IfConfigDecl> Parser::parseDeclIfConfig(ParseDeclOptions Flags) {
     if (ConfigState.shouldParse()) {
       ParserStatus Status;
       bool PreviousHadSemi = true;
-      while (Tok.isNot(tok::pound_else, tok::pound_endif, tok::pound_elseif)) {
-        SourceLoc StartLoc = Tok.getLoc();
-        Status |= parseDeclItem(*this, PreviousHadSemi, Flags,
-                                [&](Decl *D) {Decls.push_back(D);});
-        if (StartLoc == Tok.getLoc()) {
-          assert(Status.isError() && "no progress without error?");
+      while (Tok.isNot(tok::pound_else, tok::pound_endif, tok::pound_elseif,
+                       tok::eof)) {
+        if (Tok.is(tok::r_brace)) {
+          diagnose(Tok.getLoc(),
+                   diag::unexpected_rbrace_in_conditional_compilation_block);
+          // If we see '}', following declarations don't look like belong to
+          // the current decl context; skip them.
           skipUntilConditionalBlockClose();
           break;
         }
-        if (Tok.isAny(tok::eof)) {
-          diagnose(Tok, diag::expected_close_to_if_directive);
-          break;
-        }
+        Status |= parseDeclItem(*this, PreviousHadSemi, Flags,
+                                [&](Decl *D) {Decls.push_back(D);});
       }
     } else {
       DiagnosticTransaction DT(Diags);

test/Parse/ConditionalCompilation/decl_parse_errors-2.swift

@@ -0,0 +1,7 @@
+// RUN: %target-typecheck-verify-swift
+
+class C2 { // expected-note {{to match this opening '{'}}
+  #if FOO
+  func foo() {}
+// expected-error @+2 {{expected '}' in class}}
+// expected-error @+1 {{expected #else or #endif at end of conditional compilation block}}

test/Parse/ConditionalCompilation/decl_parse_errors.swift

@@ -27,14 +27,14 @@ lazy
 var val3: Int = 0;
 #line
 
-class C { // expected-note 2 {{in declaration of 'C'}} expected-note {{to match this opening '{'}}
+class C { // expected-note {{to match this opening '{'}}
 
 #if os(iOS)
 	func foo() {}
-} // expected-error{{expected declaration}}
+} // expected-error{{unexpected '}' in conditional compilation block}}
 #else
 	func bar() {}
 	func baz() {}
-} // expected-error{{expected declaration}}
+} // expected-error{{unexpected '}' in conditional compilation block}}
 #endif
 // expected-error@+1{{expected '}' in class}}