9. Release Notes

This following summarizes the most important changes in recent Spicy releases. For an exhaustive list of all changes, see the #%sCHANGES file coming with the distribution.

9.1. Version 1.6 (in progress)

New Functionality

Changed Functionality

Bug fixes


9.2. Version 1.5

New Functionality

  • GH-1179: Cap parallelism use for JIT background jobs.

    During JIT, we would previously launch all compilation jobs in parallel. For projects using many modules this could have lead to resource contention which often forced users to use sequential compilation with HILTI_JIT_SEQUENTIAL. We now by default cap the number of parallel background jobs at the number of logical cores. This can be parameterized with the environment variable HILTI_JIT_PARALLELISM which for HILTI_JIT_PARALLELISM=1 reproduces HILTI_JIT_SEQUENTIAL.

  • GH-1134: Add support for synchronize-at and synchronize-after properties.

    These unit properties allow specifying a literal which should be searched for during error recovery. If the respective unit is used as a synchronize point during error recovery, i.e., it is used as a field which is marked &synchronize, input resynchronization during error recovery will seek to the next position of this pattern in the input stream.

  • GH-1209: Provide error message to %error handler.

    We now allow to optionally provide a string parameter with %error that will receive the associated error message:

    on %error(msg: string) { print msg; }

Changed Functionality

  • GH-1184: Allow more cache hits if only a few modules are changed in multi-module compilation.

  • GH-1208: Incremental performance tweaks for JIT.

  • GH-1197: Make handling of sanitizer workarounds more granular.

Bug fixes

  • GH-1150: Preserve additional permissions from umask when generating HLTO files.

  • GH-1154: Add stringificaton of Map::value_type.

  • GH-1080: Reject constant declarations at non-global scope.

  • GH-1164: Make compiler plugin initialization explicit.

  • GH-1050: Update location when entering most parser methods.

  • GH-1187: Fix support for having multiple source modules of the same name.

  • GH-1197: Prevent too early integer overflow in pow.

  • GH-1201: Adjust removal of symlinks on install for DESTDIR.

  • GH-1203: Allow changing DESTDIR between configure and install time.

  • GH-1204: Remove potential use-after-move.

  • GH-1210: Prevent unnecessarily executable stack with GNU toolchain.

  • GH-1206: Fix detection of recursive dependencies.

  • GH-1217: Produce hilti::rt::Bool when casting to boolean.

  • GH-1224: Fix import segfault.


  • GH-44: Update docs for spicy-plugin rename _Zeek::Spicy -> Zeek::Spicy.

  • GH-1183: Update docs for Discourse migration [skip CI].

  • GH-1205: Update Spicy docs for now being built into Zeek.

9.3. Version 1.4

New Functionality

  • Add support for recovery from parse errors or incomplete input

    This release adds support for recovering from parse errors or incomplete input (e.g., gaps or partial connections). Grammars can denote unit synchronization points with a &synchronize attribute. If an error is encountered while extracting a previous fields, parsing will attempt to resynchronize the input at that point. The synchronization result needs to be checked and confirmed or rejected explicitly; a number of hooks are provided for that. See the docs for details.

  • Remove restriction that units used as sinks need to be public

  • Uses ccache for C++ compilation during JIT if Spicy itself was configured to use ccache

Spicy spends a considerable amount of JIT time compiling generated C++ code. This work can be cached if neither inputs nor any of the used flags have changed so that subsequent JIT runs can complete much faster.

We now automatically cache many C++ compilation artifacts with ccache if Spicy itself was configured with e.g., --with-hilti-compiler-launcher=ccache. This behavior can be controlled or disabled via the HILTI_CXX_COMPILER_LAUNCHER environment variable.

  • GH-842: Add Spicy support for struct initialization.

  • GH-1036: Support unit initialization through a struct constructor expression.

Changed Functionality

  • GH-1074: %random-access is now derived automatically from uses and declaring it explicitly has been deprecated.

  • GH-1072: Disallow enum declarations with non-unique values.

    It is unclear what code should be generated when requested to convert an integer value to the following enum:

    type E = enum {
        A = 1,
        B = 2,
        C = 1,

    For 1 we could produce either E::A or E::C here.

    Instead of allowing this ambiguity we now disallow enums with non-unique values.

Bug fixes

  • Prevent exception if cache directory is not readable.

  • Propagate failure from cmake up to ./configure.

  • GH-1030: Make sure types required for globals are declared before being used.

  • Fix potentially use-after-free in stringification of stream::View.

  • GH-1087: Make offset return correct value even before parsing of field.


9.4. Version 1.3

New Functionality

  • Add optimizer removing unused %random-access or %filter functionality

    If a unit has e.g., a %random-access attribute Spicy emits additional code to track and update offsets. If the %random-access functionality is not used this leads to unneeded code being emitted which causes unneeded overhead, both during JIT and during execution.

    We now emit such feature-dependent code under a feature flag (effectively a global boolean constant) which is by default on. Additionally, we added an optimizer pass which detects whether a feature is used and can disable unused feature functionality (switching the feature flag to off), and can then remove unreachable code behind such disabled feature flags by performing basic constant folding.

  • Add optimizer pass removing unused sink functionality

    By default any unit declared public can be used as a sink. To support sink behavior additional code is emitted and invoked at runtime, regardless of whether the unit is used as a sink or not.

    We now detect unused sink functionality and avoid emitting it.

  • GH-934: Allow $$ in place of self in unit convert attributes.

Changed Functionality

  • GH-941: Allow use of units with all defaulted parameters as entry points.

  • We added precompilation support for libspicy.h.

  • Drop support for end-of-life Fedora 32, and add support for Fedora 34.

Bug fixes

  • Correctly handle lookups for NULL library symbols.

  • Use safe integers for size functions in the runtime library.

  • Make it possible to build on ARM64.

  • Fix building with gcc-11.


9.5. Version 1.2

New Functionality

  • GH-913: Add support for switch-level &parse-at and &parse-from attributes inside a unit.

  • Add optimizer pass removing unimplemented functions and methods.

    This introduces a global pass triggered after all individual input ASTs have been finalized, but before we generate any C++ code. We then strip out any unimplemented member functions (typically Spicy hooks), both their definitions as well as their uses.

    In order to correctly handle previously generated C++ files which might have been generated with different optimization settings, we disallow optimizations if we detect that a C++ input file was generated by us.

Changed Functionality

  • Add validation of unit switch attributes. We previously silently ignored unsupported attributes; now errors are raised.

  • Remove configure option --build-zeek-plugin. Spicy no longer supports building the Zeek plugin/analyzers in-tree. This used to be available primarily for development purposes, but became challenging to maintain.

  • Add environment variable HILTI_CXX_INCLUDE_DIRS to specify additional C++ include directories when compiling generated code.

  • GH-940: Add runtime check for parsing progress during loops.

Bug fixes

  • Fix computation of unset locations.

  • Fix accidental truncating conversion in integer code.


9.6. Version 1.1

New Functionality

  • GH-844: Add support for &size attribute to unit switch statement.

  • GH-26: Add %skip, %skip-pre and %skip-post properties for skipping input matching a regular expression before any further input processing takes place.

  • Extend library functionality provided by the spicy module:

    • crc32_init()/crc32_add() compute CRC32 checksums.

    • mktime() creates a time value from individual components.

    • zlib_init() initializes a ZlibStream with a given window bits argument.

    • Zlib now accepts a window bits parameter.

  • Add a new find() method to units for that searches for a bytes sequence inside their input data, forward or backward from a given starting position.

  • Add support for &chunked when parsing bytes data with &until or &until_including.

  • Add encode() method to string for conversion to bytes.

  • Extend parsing of void fields:

    • Add support for &eod to skip all data until the end of the current input is encountered.

    • Add support for &until to skip all data until a deliminator is encountered. The deliminator will be extracted from the stream before continuing.

  • Port Spicy to Apple silicon.

  • Add Dockerfile for OpenSUSE 15.2.

Changed Functionality

  • Reject void fields with names.

  • Lower minimum required Python version to 3.2.

  • GH-882: Lower minimum required Bison version to 3.0.

Bug fixes

  • GH-872: Fix missing normalization of enum label IDs.

  • GH-878: Fix casting integers to enums.

  • GH-889: Fix hook handling for anonymous void fields.

  • GH-901: Fix type resolution bug in &convert.

  • Fix handling of &size attribute for anonymous void fields.

  • Fix missing update to input position before running %done hook.

  • Add validation rejecting $$ in hooks not supporting it.

  • Make sure container sizes are runtime integers.

  • Fix missing operator<< for enums when generating debug code.

  • GH-917: Default-initialize forwarding fields without type arguments.


  • GH-37: Add documentation on how to skip data with void fields.

9.7. Migrating from the old prototype

Below we summarize language changes in Spicy compared to the original research prototype. Note that some of the prototype’s more advanced functionality has not yet been ported to the new code base; see the corresponding list on GitHub for what’s still missing.


  • Renamed export linkage to public.

  • Renamed %byteorder property to %byte-order.

  • Renamed &byteorder attribute to &byte-order.

  • Renamed &bitorder attribute to &bit-order.

  • All unit-level properties now need to conclude with a semicolon (e.g., %filter;).

  • Renamed &length attribute to &size.

  • Renamed &until_including attribute to &until-including.

  • Replaced &parse with separate &parse-from (taking a “bytes” instance) and &parse-at (taking a stream iterator) attributes.

  • Attributes no longer accept their arguments in parentheses, it now must <attr>=expr. (Before, both versions were accepted.)

  • uint<N> and int<N> are no longer accepted, use uintN/intN instead (which worked before already as well)

  • list<T> is no longer supported, use vector<T> instead.

  • New syntax for parsing sequences: Use x: int8[5] instead of x: vector<int8> &length=5. For lists of unknown size, use x: int8[]. When parsing sequences sub-units, use: x: Item[]; or, if further arguments/attributes are required, x: (Item(1,2,3))[]. (The latter syntax isn’t great, but the old syntax was ambiguous.)

  • New syntax for functions: function f(<params>) [: <result>] instead of <result> f(<params>)

  • Renamed runtime support module from Spicy to spicy (so use import spicy)

  • In units, variables are now initialized to default values by default. Previously, that was (inconsistently) happening only for variables of type sink. To revert to the old behaviour, add “&optional” to the variable.

  • Renamed type double to real.

  • Generally, types don’t coerce implicitly to bool anymore except in specific language contexts, such as in statements with boolean conditions.

  • Filters can now be implemented in Spicy itself. The pre-built filter::Base64Decode and filter::Zlib provide the base64 and zlib functionality of the previously built-in filters.

  • {unit,sink}::add_filter are renamed to {unit,sink}::connect_filter.

  • Enums don’t coerce to bool anymore, need to manually compare to Undef.

  • Coercion to bool now happens only in certain contexts, like if-conditions (similar to C++).

  • The sink method sequence has been renamed to sequence_number.

  • The effect of the sink method set_initial_sequence_number no longer persists when reconnecting a different unit to a sink.

  • &transient is no longer a supported unit field attribute. The same effect can now be achieved through an anonymous field (also see next point).

  • $$ can now be generally used in hooks to refer to the just parsed value. That’s particularly useful inside hooks for anonymous fields, including fields that previously were &transient (see above). Previously, “$$” worked only for container elements in foreach hooks (which still operates the same way).

  • Fields of type real are parsed with &type attribute (e.g., &type=Spicy::RealType::IEEE754_Double). They used to &precision attributes with a different enum type.

  • Assigning to unit fields and variables no longer triggers any hooks. That also means that hooks are generally no longer supported for variables (This is tricky to implement, not clear it’s worth the effort.)

  • When importing modules, module names are now case-sensitive.

  • When parsing vectors/lists of integers of a given length, use &count instead of &length.

  • Zeek plugin:

    • Bro::dpd_confirm() has been renamed to zeek::confirm_protocol(). There’s also a corresponding zeek::reject_protocol().

    • To auto-export enums to Zeek, they need to be declared public.