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Adding features

Table of contents

Lex

New lexed tokens must be added to token_kind.def. CARBON_SYMBOL_TOKEN and CARBON_KEYWORD_TOKEN both provide some built-in lexing logic, while CARBON_TOKEN requires custom lexing support.

TokenizedBuffer::Lex is the main dispatch for lexing, and calls that need to do custom lexing will be dispatched there.

Parse

A parser feature will have state transitions that produce new parse nodes.

The resulting parse nodes are in parse/node_kind.def and typed_nodes.h. When choosing node structure, consider how semantics will process it in post-order; this will rule out some designs. Adding a parse node kind will also require a handler in the Check step.

The state transitions are in parse/state.def. Each CARBON_PARSER_STATE defines a distinct state and has comments for state transitions. If several states should share handling, name them FeatureAsVariant.

Adding a state requires adding a Handle<name> function in an appropriate parse/handle_*.cpp file, possibly a new file. The macros are used to generate declarations in the header, so only extra helper functions should be added there. Every state handler pops the state from the stack before any other processing.

Typed parse node metadata implementation

As of #3534:

parse

TODO: Convert this chart to Mermaid.

  • common/enum_base.h defines the EnumBase CRTP class extending Printable from common/ostream.h, along with CARBON_ENUM macros for making enumerations

  • parse/node_kind.h includes common/enum_base.h and defines an enumeration NodeKind, along with bitmask enum NodeCategory.

    • The NodeKind enumeration is populated with the list of all parse node kinds using parse/node_kind.def (using the .def file idiom) declared in this file using a macro from common/enum_base.h

    • NodeKind has a member type NodeKind::Definition that extends NodeKind and adds a NodeCategory field (and others in the future).

    • NodeKind has a method Define for creating a NodeKind::Definition with the same enumerant value, plus values for the other fields.

    • HasKindMember<T> at the bottom of parse/node_kind.h uses field detection to determine if the type T has a NodeKind::Definition Kind static constant member.

      • Note: both the type and name of these fields must match exactly.

    • Note that additional information is needed to define the category() method (and other methods in the future) of NodeKind. This information comes from the typed parse node definitions in parse/typed_nodes.h (described below).

  • parse/node_ids.h defines a number of types that store a node id that identifies a node in the parse tree

    • NodeId stores a node id with no restrictions

    • NodeIdForKind<Kind> inherits from NodeId and stores the id of a node that must have the specified NodeKind "Kind". Note that this is not used directly, instead aliases FooId for NodeIdForKind<NodeKind::Foo> are defined for every node kind using parse/node_kind.def (using the .def file idiom).

    • NodeIdInCategory<Category> inherits from NodeId and stores the id of a node that must overlap the specified NodeCategory "Category". Note that this is not typically used directly, instead this file defines aliases AnyDeclId, AnyExprId, ..., AnyStatementId.

    • Similarly NodeIdOneOf<T, U> and NodeIdNot<V> inherit from NodeId and stores the id of a node restricted to either matching T::Kind or U::Kind or not matching V::Kind.

    • In addition to the node id type definitions above, the struct NodeForId<T> is declared but not defined.

  • parse/typed_nodes.h defines a typed parse node struct type for each kind of parse node.

    • Each one defines a static constant named Kind that is set using a call to Define() on the corresponding enumerant member of NodeKind from parse/node_kind.h (which is included by this file).

    • The fields of these types specify the children of the parse node using the types from parse/node_ids.h.

    • The struct NodeForId<T> that is declared in parse/node_ids.h is defined in this file such that NodeForId<FooId>::TypedNode is the Foo typed parse node struct type.

    • This file will fail to compile unless every kind of parse node kind defined in parse/node_kind.def has a corresponding struct type in this file.

  • parse/node_kind.cpp includes both parse/node_kind.h and parse/typed_nodes.h

    • Uses the macro from common/enum_base.h, the enumerants of NodeKind are defined using the list of parse node kinds from parse/node_kind.def (using the .def file idiom).

    • NodeKind::definition() is defined. It has a static table of const NodeKind::Definition* indexed by the enum value, populated by taking the address of the Kind member of each typed parse node struct type, using the list from parse/node_kind.def.

    • NodeKind::category() is defined using NodeKind::definition().

    • Tested assumption: the tables built in this file are indexed by the enum values. We rely on the fact that we get the parse node kinds in the same order by consistently using parse/node_kind.def.

  • parse/tree.h includes parse/node_ids.h. It does not depend on parse/typed_nodes.h to reduce compilation time in those files that don't use the typed parse node struct types.

    • Defines Tree::Extract... functions that take a node id and return a typed parse node struct type from parse/typed_nodes.h.

    • Uses HasKindMember<T> to restrict calling ExtractAs except on typed nodes defined in parse/typed_nodes.h.

    • Tree::Extract uses NodeForId<T> to get the corresponding typed parse node struct type for a FooId type defined in parse/node_ids.h.

      • Note that this is done without a dependency on the typed parse node struct types by using the forward declaration of NodeForId<T> from parse/node_ids.h.

    • The Tree::Extract... functions ultimately call Tree::TryExtractNodeFromChildren<T>, which is a templated function only declared in this file. Its definition is in parse/extract.cpp.

  • parse/extract.cpp includes parse/tree.h and parse/typed_nodes.h

    • Defines struct Extractable<T> that defines how to extract a field of type T from a Tree::SiblingIterator pointing at the corresponding child node.

    • Extractable<T> is defined for the node id types defined in parse/node_ids.h.

    • In addition, Extractable<T> is defined for standard types std::optional<U> and llvm::SmallVector<V>, to support optional and repeated children.

    • Uses struct reflection to support aggregate struct types containing extractable fields. This is used to support typed parse node struct types as well as struct fields that they contain.

    • Uses HasKindMember<Foo> to detect accidental uses of a parse node type directly as fields of typed parse node struct types -- in those places FooId should be used instead.

    • Defines Tree::TryExtractNodeFromChildren<T> and explicitly instantiates it for every typed parse node struct type defined in parse/typed_nodes.h using parse/node_kind.def (using the .def file idiom). By explicitly instantiating this function only in this file, we avoid redundant compilation work, which reduces build times, and allow us to keep all the extraction machinery as a private implementation detail of this file.

  • parse/typed_nodes_test.cpp validates that each typed parse node struct type has a static Kind member that defines the correct corresponding NodeKind, and that the category() function agrees between the NodeKind and NodeKind::Definition.

Note: this is broadly similar to SemIR typed instruction metadata implementation.

Check

Each parse node kind requires adding a Handle<kind> function in a check/handle_*.cpp file.

If the resulting SemIR needs a new instruction:

  • add a new kind to sem_ir/inst_kind.def

    • Add a CARBON_SEM_IR_INST_KIND(NewInstKindName) line in alphabetical order

  • a new struct definition to sem_ir/typed_insts.h, such as:

    struct NewInstKindName {
    static constexpr auto Kind = InstKind::NewInstKindName.Define(
        // the name used in textual IR
        "new_inst_kind_name"
        // Optional: , TerminatorKind::KindOfTerminator
        );

    // Optional: omit if not associated with a parse node.
    Parse::Node parse_node;

    // Optional: omit if this sem_ir instruction does not produce a value.
    TypeId type_id;

    // 0-2 id fields, with types from sem_ir/ids.h or sem_ir/builtin_kind.h
    // For example, fields would look like:
    StringId name_id;
    InstId value_id;
};

Adding an instruction will also require a handler in the Lower step.

Most new instructions will automatically be formatted reasonably by the SemIR formatter.

If the resulting SemIR needs a new built-in, add it to builtin_inst_kind.def.

SemIR typed instruction metadata implementation

How does this work? As of #3310:

check

TODO: Convert this chart to Mermaid.

  • common/enum_base.h defines the EnumBase CRTP class extending Printable from common/ostream.h, along with CARBON_ENUM macros for making enumerations

  • sem_ir/inst_kind.h includes common/enum_base.h and defines an enumeration InstKind, along with InstValueKind and TerminatorKind.

    • The InstKind enumeration is populated with the list of all instruction kinds using sem_ir/inst_kind.def (using the .def file idiom) declared in this file using a macro from common/enum_base.h

    • InstKind has a member type InstKind::Definition that extends InstKind and adds the ir_name string field, and a TerminatorKind field.

    • InstKind has a method Define for creating a InstKind::Definition with the same enumerant value, plus values for the other fields.

  • Note that additional information is needed to define the ir_name(), value_kind(), and terminator_kind() methods of InstKind. This information comes from the typed instruction definitions in sem_ir/typed_insts.h.

  • sem_ir/typed_insts.h defines a typed instruction struct type for each kind of SemIR instruction, as described above.

    • Each one defines a static constant named Kind that is set using a call to Define() on the corresponding enumerant member of InstKind from sem_ir/inst_kind.h (which is included by this file).

  • HasParseNodeMember<TypedInst> and HasTypeIdMember<TypedInst> at the bottom of sem_ir/typed_insts.h use field detection to determine if TypedInst has a Parse::Node parse_node or a TypeId type_id field respectively.

    • Note: both the type and name of these fields must match exactly.

  • sem_ir/inst_kind.cpp includes both sem_ir/inst_kind.h and sem_ir/typed_insts.h

    • Uses the macro from common/enum_base.h, the enumerants of InstKind are defined using the list of instruction kinds from sem_ir/inst_kind.def (using the .def file idiom)

    • InstKind::value_kind() is defined. It has a static table of InstValueKind values indexed by the enum value, populated by applying HasTypeIdMember from sem_ir/typed_insts.h to every instruction kind by using the list from sem_ir/inst_kind.def.

    • InstKind::definition() is defined. It has a static table of const InstKind::Definition* indexed by the enum value, populated by taking the address of the Kind member of each TypedInst, using the list from sem_ir/inst_kind.def.

    • InstKind::ir_name() and InstKind::terminator_kind() are defined using InstKind::definition().

    • Tested assumption: the tables built in this file are indexed by the enum values. We rely on the fact that we get the instruction kinds in the same order by consistently using sem_ir/inst_kind.def.

    • This file will fail to compile unless every kind of SemIR instruction defined in sem_ir/inst_kind.def has a corresponding struct type in sem_ir/typed_insts.h.

  • TypedInstArgsInfo<TypedInst> defined in sem_ir/inst.h uses struct reflection to determine the other fields from TypedInst. It skips the parse_node and type_id fields using HasParseNodeMember<TypedInst> and HasTypeIdMember<TypedInst>.

    • Tested assumption: the parse_node and type_id are the first fields in TypedInst, and there are at most two more fields.

  • sem_ir/inst.h defines templated conversions between Inst and each of the typed instruction structs:

    • Uses TypedInstArgsInfo<TypedInst>, HasParseNodeMember<TypedInst>, and HasTypeIdMember<TypedInst>, and local lambda.

    • Defines a templated ToRaw function that converts the various id field types to an int32_t.

    • Defines a templated FromRaw<T> function that converts an int32_t to T to perform the opposite conversion.

    • Tested assumption: The parse_node field is first, when present, and the type_id is next, when present, in each TypedInst struct type.

  • The "tested assumptions" above are all tested by sem_ir/typed_insts_test.cpp

Lower

Each SemIR instruction requires adding a Handle<kind> function in a lower/handle_*.cpp file.

Tests and debugging

Running tests

Tests are run in bulk as bazel test //toolchain/.... Many tests are using the file_test infrastructure; see testing/file_test/README.md for information.

There are several supported ways to run Carbon on a given test file. For example, with toolchain/parse/testdata/basics/empty.carbon:

  • bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/basics/empty.carbon
    • Executes an individual test.
  • bazel run //toolchain/parse:testdata/basics/empty.carbon.run
    • Runs carbon on the file with standard arguments, printing output to console.
    • This form will often be most useful when iterating over a specific test.
  • bazel run //toolchain/parse:testdata/basics/empty.carbon.verbose
    • Similar to the previous command, but with the -v flag implied.
  • bazel run //toolchain/driver:carbon -- compile --phase=parse --dump-parse-tree toolchain/parse/testdata/basics/empty.carbon
    • Explicitly runs carbon with the provided arguments.
  • bazel-bin/toolchain/driver/carbon compile --phase=parse --dump-parse-tree toolchain/parse/testdata/basics/empty.carbon
    • Similar to the previous command, but without using bazel.

Updating tests

The toolchain/autoupdate_testdata.py script can be used to update output. It invokes the file_test autoupdate support. See testing/file_test/README.md for file syntax.

Reviewing test deltas

Using autoupdate_testdata.py can be useful to produce deltas during the development process because it allows git status and git diff to be used to examine what changed.

Verbose output

The -v flag can be passed to trace state, and should be specified before the subcommand name: carbon -v compile .... CARBON_VLOG is used to print output in this mode. There is currently no control over the degree of verbosity.

Stack traces

While the iterative processing pattern means function stack traces will have minimal context for how the current function is reached, we use LLVM's PrettyStackTrace to include details about the state stack. The state stack will be above the function stack in crash output.