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# Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
# Licensed under the MIT License:
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
using Cxx = import "/capnp/c++.capnp";
using Id = UInt64;
# The globally-unique ID of a file, type, or annotation.
struct Node {
id @0 :Id;
displayName @1 :Text;
# Name to present to humans to identify this Node. You should not attempt to parse this. Its
# format could change. It is not guaranteed to be unique.
# (On Zooko's triangle, this is the node's nickname.)
displayNamePrefixLength @2 :UInt32;
# If you want a shorter version of `displayName` (just naming this node, without its surrounding
# scope), chop off this many characters from the beginning of `displayName`.
scopeId @3 :Id;
# ID of the lexical parent node. Typically, the scope node will have a NestedNode pointing back
# at this node, but robust code should avoid relying on this (and, in fact, group nodes are not
# listed in the outer struct's nestedNodes, since they are listed in the fields). `scopeId` is
# zero if the node has no parent, which is normally only the case with files, but should be
# allowed for any kind of node (in order to make runtime type generation easier).
parameters @32 :List(Parameter);
# If this node is parameterized (generic), the list of parameters. Empty for non-generic types.
isGeneric @33 :Bool;
# True if this node is generic, meaning that it or one of its parent scopes has a non-empty
# `parameters`.
struct Parameter {
# Information about one of the node's parameters.
name @0 :Text;
nestedNodes @4 :List(NestedNode);
# List of nodes nested within this node, along with the names under which they were declared.
struct NestedNode {
name @0 :Text;
# Unqualified symbol name. Unlike Node.displayName, this *can* be used programmatically.
# (On Zooko's triangle, this is the node's petname according to its parent scope.)
id @1 :Id;
# ID of the nested node. Typically, the target node's scopeId points back to this node, but
# robust code should avoid relying on this.
annotations @5 :List(Annotation);
# Annotations applied to this node.
union {
# Info specific to each kind of node.
file @6 :Void;
struct :group {
dataWordCount @7 :UInt16;
# Size of the data section, in words.
pointerCount @8 :UInt16;
# Size of the pointer section, in pointers (which are one word each).
preferredListEncoding @9 :ElementSize;
# The preferred element size to use when encoding a list of this struct. If this is anything
# other than `inlineComposite` then the struct is one word or less in size and is a candidate
# for list packing optimization.
isGroup @10 :Bool;
# If true, then this "struct" node is actually not an independent node, but merely represents
# some named union or group within a particular parent struct. This node's scopeId refers
# to the parent struct, which may itself be a union/group in yet another struct.
# All group nodes share the same dataWordCount and pointerCount as the top-level
# struct, and their fields live in the same ordinal and offset spaces as all other fields in
# the struct.
# Note that a named union is considered a special kind of group -- in fact, a named union
# is exactly equivalent to a group that contains nothing but an unnamed union.
discriminantCount @11 :UInt16;
# Number of fields in this struct which are members of an anonymous union, and thus may
# overlap. If this is non-zero, then a 16-bit discriminant is present indicating which
# of the overlapping fields is active. This can never be 1 -- if it is non-zero, it must be
# two or more.
# Note that the fields of an unnamed union are considered fields of the scope containing the
# union -- an unnamed union is not its own group. So, a top-level struct may contain a
# non-zero discriminant count. Named unions, on the other hand, are equivalent to groups
# containing unnamed unions. So, a named union has its own independent schema node, with
# `isGroup` = true.
discriminantOffset @12 :UInt32;
# If `discriminantCount` is non-zero, this is the offset of the union discriminant, in
# multiples of 16 bits.
fields @13 :List(Field);
# Fields defined within this scope (either the struct's top-level fields, or the fields of
# a particular group; see `isGroup`).
# The fields are sorted by ordinal number, but note that because groups share the same
# ordinal space, the field's index in this list is not necessarily exactly its ordinal.
# On the other hand, the field's position in this list does remain the same even as the
# protocol evolves, since it is not possible to insert or remove an earlier ordinal.
# Therefore, for most use cases, if you want to identify a field by number, it may make the
# most sense to use the field's index in this list rather than its ordinal.
enum :group {
enumerants@14 :List(Enumerant);
# Enumerants ordered by numeric value (ordinal).
interface :group {
methods @15 :List(Method);
# Methods ordered by ordinal.
superclasses @31 :List(Superclass);
# Superclasses of this interface.
const :group {
type @16 :Type;
value @17 :Value;
annotation :group {
type @18 :Type;
targetsFile @19 :Bool;
targetsConst @20 :Bool;
targetsEnum @21 :Bool;
targetsEnumerant @22 :Bool;
targetsStruct @23 :Bool;
targetsField @24 :Bool;
targetsUnion @25 :Bool;
targetsGroup @26 :Bool;
targetsInterface @27 :Bool;
targetsMethod @28 :Bool;
targetsParam @29 :Bool;
targetsAnnotation @30 :Bool;
struct SourceInfo {
# Additional information about a node which is not needed at runtime, but may be useful for
# documentation or debugging purposes. This is kept in a separate struct to make sure it
# doesn't accidentally get included in contexts where it is not needed. The
# `CodeGeneratorRequest` includes this information in a separate array.
id @0 :Id;
# ID of the Node which this info describes.
docComment @1 :Text;
# The top-level doc comment for the Node.
members @2 :List(Member);
# Information about each member -- i.e. fields (for structs), enumerants (for enums), or
# methods (for interfaces).
# This list is the same length and order as the corresponding list in the Node, i.e.
# Node.struct.fields, Node.enum.enumerants, or Node.interface.methods.
struct Member {
docComment @0 :Text;
# Doc comment on the member.
# TODO(someday): Record location of the declaration in the original source code.
struct Field {
# Schema for a field of a struct.
name @0 :Text;
codeOrder @1 :UInt16;
# Indicates where this member appeared in the code, relative to other members.
# Code ordering may have semantic relevance -- programmers tend to place related fields
# together. So, using code ordering makes sense in human-readable formats where ordering is
# otherwise irrelevant, like JSON. The values of codeOrder are tightly-packed, so the maximum
# value is count(members) - 1. Fields that are members of a union are only ordered relative to
# the other members of that union, so the maximum value there is count(union.members).
annotations @2 :List(Annotation);
const noDiscriminant :UInt16 = 0xffff;
discriminantValue @3 :UInt16 = Field.noDiscriminant;
# If the field is in a union, this is the value which the union's discriminant should take when
# the field is active. If the field is not in a union, this is 0xffff.
union {
slot :group {
# A regular, non-group, non-fixed-list field.
offset @4 :UInt32;
# Offset, in units of the field's size, from the beginning of the section in which the field
# resides. E.g. for a UInt32 field, multiply this by 4 to get the byte offset from the
# beginning of the data section.
type @5 :Type;
defaultValue @6 :Value;
hadExplicitDefault @10 :Bool;
# Whether the default value was specified explicitly. Non-explicit default values are always
# zero or empty values. Usually, whether the default value was explicit shouldn't matter.
# The main use case for this flag is for structs representing method parameters:
# explicitly-defaulted parameters may be allowed to be omitted when calling the method.
group :group {
# A group.
typeId @7 :Id;
# The ID of the group's node.
ordinal :union {
implicit @8 :Void;
explicit @9 :UInt16;
# The original ordinal number given to the field. You probably should NOT use this; if you need
# a numeric identifier for a field, use its position within the field array for its scope.
# The ordinal is given here mainly just so that the original schema text can be reproduced given
# the compiled version -- i.e. so that `capnp compile -ocapnp` can do its job.
struct Enumerant {
# Schema for member of an enum.
name @0 :Text;
codeOrder @1 :UInt16;
# Specifies order in which the enumerants were declared in the code.
# Like Struct.Field.codeOrder.
annotations @2 :List(Annotation);
struct Superclass {
id @0 :Id;
brand @1 :Brand;
struct Method {
# Schema for method of an interface.
name @0 :Text;
codeOrder @1 :UInt16;
# Specifies order in which the methods were declared in the code.
# Like Struct.Field.codeOrder.
implicitParameters @7 :List(Node.Parameter);
# The parameters listed in [] (typically, type / generic parameters), whose bindings are intended
# to be inferred rather than specified explicitly, although not all languages support this.
paramStructType @2 :Id;
# ID of the parameter struct type. If a named parameter list was specified in the method
# declaration (rather than a single struct parameter type) then a corresponding struct type is
# auto-generated. Such an auto-generated type will not be listed in the interface's
# `nestedNodes` and its `scopeId` will be zero -- it is completely detached from the namespace.
# (Awkwardly, it does of course inherit generic parameters from the method's scope, which makes
# this a situation where you can't just climb the scope chain to find where a particular
# generic parameter was introduced. Making the `scopeId` zero was a mistake.)
paramBrand @5 :Brand;
# Brand of param struct type.
resultStructType @3 :Id;
# ID of the return struct type; similar to `paramStructType`.
resultBrand @6 :Brand;
# Brand of result struct type.
annotations @4 :List(Annotation);
struct Type {
# Represents a type expression.
union {
# The ordinals intentionally match those of Value.
void @0 :Void;
bool @1 :Void;
int8 @2 :Void;
int16 @3 :Void;
int32 @4 :Void;
int64 @5 :Void;
uint8 @6 :Void;
uint16 @7 :Void;
uint32 @8 :Void;
uint64 @9 :Void;
float32 @10 :Void;
float64 @11 :Void;
text @12 :Void;
data @13 :Void;
list :group {
elementType @14 :Type;
enum :group {
typeId @15 :Id;
brand @21 :Brand;
struct :group {
typeId @16 :Id;
brand @22 :Brand;
interface :group {
typeId @17 :Id;
brand @23 :Brand;
anyPointer :union {
unconstrained :union {
# A regular AnyPointer.
# The name "unconstrained" means as opposed to constraining it to match a type parameter.
# In retrospect this name is probably a poor choice given that it may still be constrained
# to be a struct, list, or capability.
anyKind @18 :Void; # truly AnyPointer
struct @25 :Void; # AnyStruct
list @26 :Void; # AnyList
capability @27 :Void; # Capability
parameter :group {
# This is actually a reference to a type parameter defined within this scope.
scopeId @19 :Id;
# ID of the generic type whose parameter we're referencing. This should be a parent of the
# current scope.
parameterIndex @20 :UInt16;
# Index of the parameter within the generic type's parameter list.
implicitMethodParameter :group {
# This is actually a reference to an implicit (generic) parameter of a method. The only
# legal context for this type to appear is inside Method.paramBrand or Method.resultBrand.
parameterIndex @24 :UInt16;
struct Brand {
# Specifies bindings for parameters of generics. Since these bindings turn a generic into a
# non-generic, we call it the "brand".
scopes @0 :List(Scope);
# For each of the target type and each of its parent scopes, a parameterization may be included
# in this list. If no parameterization is included for a particular relevant scope, then either
# that scope has no parameters or all parameters should be considered to be `AnyPointer`.
struct Scope {
scopeId @0 :Id;
# ID of the scope to which these params apply.
union {
bind @1 :List(Binding);
# List of parameter bindings.
inherit @2 :Void;
# The place where the Brand appears is within this scope or a sub-scope, and bindings
# for this scope are deferred to later Brand applications. This is equivalent to a
# pass-through binding list, where each of this scope's parameters is bound to itself.
# For example:
# struct Outer(T) {
# struct Inner {
# value @0 :T;
# }
# innerInherit @0 :Inner; # Outer Brand.Scope is `inherit`.
# innerBindSelf @1 :Outer(T).Inner; # Outer Brand.Scope explicitly binds T to T.
# }
# The innerInherit and innerBindSelf fields have equivalent types, but different Brand
# styles.
struct Binding {
union {
unbound @0 :Void;
type @1 :Type;
# TODO(someday): Allow non-type parameters? Unsure if useful.
struct Value {
# Represents a value, e.g. a field default value, constant value, or annotation value.
union {
# The ordinals intentionally match those of Type.
void @0 :Void;
bool @1 :Bool;
int8 @2 :Int8;
int16 @3 :Int16;
int32 @4 :Int32;
int64 @5 :Int64;
uint8 @6 :UInt8;
uint16 @7 :UInt16;
uint32 @8 :UInt32;
uint64 @9 :UInt64;
float32 @10 :Float32;
float64 @11 :Float64;
text @12 :Text;
data @13 :Data;
list @14 :AnyPointer;
enum @15 :UInt16;
struct @16 :AnyPointer;
interface @17 :Void;
# The only interface value that can be represented statically is "null", whose methods always
# throw exceptions.
anyPointer @18 :AnyPointer;
struct Annotation {
# Describes an annotation applied to a declaration. Note AnnotationNode describes the
# annotation's declaration, while this describes a use of the annotation.
id @0 :Id;
# ID of the annotation node.
brand @2 :Brand;
# Brand of the annotation.
# Note that the annotation itself is not allowed to be parameterized, but its scope might be.
value @1 :Value;
enum ElementSize {
# Possible element sizes for encoded lists. These correspond exactly to the possible values of
# the 3-bit element size component of a list pointer.
empty @0; # aka "void", but that's a keyword.
bit @1;
byte @2;
twoBytes @3;
fourBytes @4;
eightBytes @5;
pointer @6;
inlineComposite @7;
struct CapnpVersion {
major @0 :UInt16;
minor @1 :UInt8;
micro @2 :UInt8;
struct CodeGeneratorRequest {
capnpVersion @2 :CapnpVersion;
# Version of the `capnp` executable. Generally, code generators should ignore this, but the code
# generators that ship with `capnp` itself will print a warning if this mismatches since that
# probably indicates something is misconfigured.
# The first version of 'capnp' to set this was 0.6.0. So, if it's missing, the compiler version
# is older than that.
nodes @0 :List(Node);
# All nodes parsed by the compiler, including for the files on the command line and their
# imports.
sourceInfo @3 :List(Node.SourceInfo);
# Information about the original source code for each node, where available. This array may be
# omitted or may be missing some nodes if no info is available for them.
requestedFiles @1 :List(RequestedFile);
# Files which were listed on the command line.
struct RequestedFile {
id @0 :Id;
# ID of the file.
filename @1 :Text;
# Name of the file as it appeared on the command-line (minus the src-prefix). You may use
# this to decide where to write the output.
imports @2 :List(Import);
# List of all imported paths seen in this file.
struct Import {
id @0 :Id;
# ID of the imported file.
name @1 :Text;
# Name which *this* file used to refer to the foreign file. This may be a relative name.
# This information is provided because it might be useful for code generation, e.g. to
# generate #include directives in C++. We don't put this in Node.file because this
# information is only meaningful at compile time anyway.
# (On Zooko's triangle, this is the import's petname according to the importing file.)