Avoid parse errors for C++ attributes

Just ignore anything in between [[ and ]] in the scanner, which is better
that failing with a parse error.

Fixes #1158
Fixes #2286

Examples/test-suite/common.mk

@@ -583,6 +583,7 @@ CPP11_TEST_CASES += \
 	cpp11_alias_nested_template_scoping \
 	cpp11_alignment \
 	cpp11_alternate_function_syntax \
+	cpp11_attribute_specifiers \
 	cpp11_constexpr \
 	cpp11_decltype \
 	cpp11_default_delete \

Examples/test-suite/cpp11_attribute_specifiers.i

@@ -0,0 +1,41 @@
+%module cpp11_attribute_specifiers
+
+%inline %{
+
+#if defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations" // We're using a deprecated attribute here...
+#pragma GCC diagnostic ignored "-Wattributes"              // likely is C++20
+#pragma GCC diagnostic ignored "-Wunused-variable"         // We are using an unused variable on purpose here
+#pragma GCC diagnostic ignored "-Wunused-parameter"        // We are using an unused param on purpose here
+#endif
+
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#pragma clang diagnostic ignored "-Wattributes"
+#pragma clang diagnostic ignored "-Wunused-variable"
+#pragma clang diagnostic ignored "-Wunused-parameter"
+#endif
+
+
+[[noreturn]] void noReturn() { throw; }
+[[nodiscard]] bool noDiscard() { return true; }
+[[nodiscard, deprecated("This has been replaced")]] bool noDiscardDeprecated() { return true; }
+void maybeUnused1([[maybe_unused]] bool b) { }
+bool maybeUnused2(bool a, [[maybe_unused]] bool b) { return a; }
+
+[[deprecated, nodiscard]] bool likely([[maybe_unused]] bool a, bool b) {
+  [[maybe_unused]] bool c = b;
+  if (b) [[likely]] {
+    return true;
+  } else [[unlikely]] {
+    if(a) {
+      return true;
+    }
+  }
+  return false;
+}
+
+struct [[nodiscard]] S { };
+
+%}

Source/CParse/cscanner.c

@@ -354,6 +354,18 @@ static int yylook(void) {
     case SWIG_TOKEN_ELLIPSIS:
       return ELLIPSIS;
 
+    case SWIG_TOKEN_LLBRACKET:
+      do {
+        tok = Scanner_token(scan);
+      } while ((tok != SWIG_TOKEN_RRBRACKET) && (tok > 0));
+      if (tok <= 0) {
+        Swig_error(cparse_file, cparse_line, "Unbalanced double brackets, missing closing (']]'). Reached end of input.\n");
+      }
+      break;
+
+    case SWIG_TOKEN_RRBRACKET:
+      return RRBRACKET;
+
       /* Look for multi-character sequences */
       
     case SWIG_TOKEN_RSTRING:

Source/CParse/parser.y

@@ -1613,6 +1613,7 @@ static String *add_qualifier_to_declarator(SwigType *type, SwigType *qualifier)
 %token <type> TYPE_INT TYPE_UNSIGNED TYPE_SHORT TYPE_LONG TYPE_FLOAT TYPE_DOUBLE TYPE_CHAR TYPE_WCHAR TYPE_VOID TYPE_SIGNED TYPE_BOOL TYPE_COMPLEX TYPE_TYPEDEF TYPE_RAW TYPE_NON_ISO_INT8 TYPE_NON_ISO_INT16 TYPE_NON_ISO_INT32 TYPE_NON_ISO_INT64
 %token LPAREN RPAREN COMMA SEMI EXTERN INIT LBRACE RBRACE PERIOD ELLIPSIS
 %token CONST_QUAL VOLATILE REGISTER STRUCT UNION EQUAL SIZEOF MODULE LBRACKET RBRACKET
+%token LLBRACKET RRBRACKET  /* C++11 Attribute specifier sequence */
 %token BEGINFILE ENDOFFILE
 %token ILLEGAL CONSTANT
 %token NAME RENAME NAMEWARN EXTEND PRAGMA FEATURE VARARGS

Source/Swig/scanner.c

@@ -596,10 +596,6 @@ static int look(Scanner *s) {
 	state = 3;
       else if (c == '\\')
 	return SWIG_TOKEN_BACKSLASH;
-      else if (c == '[')
-	return SWIG_TOKEN_LBRACKET;
-      else if (c == ']')
-	return SWIG_TOKEN_RBRACKET;
       else if (c == '@')
 	return SWIG_TOKEN_AT;
       else if (c == '$')
@@ -637,6 +633,10 @@ static int look(Scanner *s) {
 
       else if (c == '.')
 	state = 100;		/* Maybe a number, maybe ellipsis, just a period */
+      else if (c == '[')
+        state = 102;            /* Maybe a bracket or a double bracket */
+      else if (c == ']')
+        state = 103;            /* Maybe a bracket or a double bracket */
       else if (isdigit(c))
 	state = 8;		/* A numerical value */
       else
@@ -1358,6 +1358,31 @@ static int look(Scanner *s) {
       }
       break;
 
+    /* A left bracket or a double left bracket */
+    case 102:
+
+      if ((c = nextchar(s)) == 0) {
+        return SWIG_TOKEN_LBRACKET;
+      } else if (c == '[') {
+        return SWIG_TOKEN_LLBRACKET;
+      } else {
+        retract(s, 1);
+        return SWIG_TOKEN_LBRACKET;
+      }
+      break;
+
+    /* a right bracket or a double right bracket */
+    case 103:
+      if ((c = nextchar(s)) == 0) {
+        return SWIG_TOKEN_RBRACKET;
+      } else if (c == ']') {
+        return SWIG_TOKEN_RRBRACKET;
+      } else {
+        retract(s, 1);
+        return SWIG_TOKEN_RBRACKET;
+      }
+      break;
+
     case 200:			/* PLUS, PLUSPLUS, PLUSEQUAL */
       if ((c = nextchar(s)) == 0)
 	return SWIG_TOKEN_PLUS;

Source/Swig/swigscan.h

@@ -71,6 +71,8 @@ extern void         Scanner_locator(Scanner *, String *loc);
 #define   SWIG_TOKEN_WSTRING      33       /* L"str" */
 #define   SWIG_TOKEN_WCHAR        34       /* L'c' */
 #define   SWIG_TOKEN_ELLIPSIS     35       /* ... */
+#define   SWIG_TOKEN_LLBRACKET    36       /* [[ */
+#define   SWIG_TOKEN_RRBRACKET    37       /* ]] */
 
 #define   SWIG_TOKEN_ILLEGAL      99
 #define   SWIG_TOKEN_ERROR        -1