Out of bounds error on incomple function default parameters

[the-horo]

Trying to parse the code void foo(int s = is causing an out-of-bounds error:

core.exception.ArrayIndexError@/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d(9104): index [6] is out of bounds for array of length 6
----------------
??:? onArrayIndexError [0x7f0e1e4139be]
??:? _d_arraybounds_indexp [0x7f0e1e413fff]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:9104 const pure nothrow @property @nogc @safe std.experimental.lexer.TokenStructure!(ubyte, "import dparse.lexer:TokenTriviaFields,TriviaToken; mixin TokenTriviaFields;").TokenStructure dparse.parser.Parser.current() [0x565523b92951]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:7325 dparse.ast.TemplateValueParameterDefault dparse.parser.Parser.parseTemplateValueParameterDefault() [0x565523b8d125]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:7295 dparse.ast.TemplateValueParameter dparse.parser.Parser.parseTemplateValueParameter() [0x565523b8d026]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:7112 dparse.ast.TemplateParameter dparse.parser.Parser.parseTemplateParameter() [0x565523b8c56c]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:8821 dparse.ast.TemplateParameterList dparse.parser.Parser.parseCommaSeparatedRule!(dparse.ast.TemplateParameterList, dparse.ast.TemplateParameter, false).parseCommaSeparatedRule(bool) [0x565523b9afb3]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:7132 dparse.ast.TemplateParameterList dparse.parser.Parser.parseTemplateParameterList() [0x565523b8c61d]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:7148 dparse.ast.TemplateParameters dparse.parser.Parser.parseTemplateParameters() [0x565523b8c686]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:2669 dparse.ast.Declarator dparse.parser.Parser.parseDeclarator() [0x565523b7d7bc]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:8107 dparse.ast.VariableDeclaration dparse.parser.Parser.parseVariableDeclaration(dparse.ast.Type, bool) [0x565523b8fb17]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:2492 dparse.ast.Declaration dparse.parser.Parser.parseDeclaration(bool, bool, bool) [0x565523b7ca7e]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:5046 dparse.ast.Module dparse.parser.Parser.parseModule() [0x565523b85a51]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:71 dparse.ast.Module dparse.parser.parseModule!().parseModule(dparse.parser.ParserConfig) [0x565523b031c8]
/home/happy/.dub/packages/libdparse/~master/libdparse/src/dparse/parser.d:100 dparse.ast.Module dparse.parser.parseModule!().parseModule(const(std.experimental.lexer.TokenStructure!(ubyte, "import dparse.lexer:TokenTriviaFields,TriviaToken; mixin TokenTriviaFields;").TokenStructure)[], immutable(char)[], dparse.rollback_allocator.RollbackAllocator*, , uint*, uint*) [0x565523b0314d]
./a.d:23 _Dmain [0x565523aff767]
Error Program exited with code 1

The above stack trace is from the modified README example below:

/+dub.sdl:
dependency "libdparse" version="~master"
+/
import dparse.ast;
import std.stdio, std.range;

class TestVisitor : ASTVisitor {}

void main()
{
    import dparse.lexer;
    import dparse.parser : parseModule;
    import dparse.rollback_allocator : RollbackAllocator;

    auto sourceCode = q{
        void foo(int s =
    };
    LexerConfig config;
    auto cache = StringCache(StringCache.defaultBucketCount);
    auto tokens = getTokensForParser(sourceCode, config, &cache);

    RollbackAllocator rba;
    auto m = parseModule(tokens, "test.d", &rba);
    auto visitor = new TestVisitor();
    visitor.visit(m);
}

I hit this in serve-d when it crashed after I saved an incomplete buffer that contained the snippet.