# Porting notes for new AST # ## Pointer Types ## * raw pointer `T*` is used for construction, but not storage * `ast::ptr_base` is a pointer to AST node `T` with reference type `R` * specialization: strong pointer `ast::ptr` is used for an ownership relationship * specialization: weak pointer `ast::readonly` is used for an observation relationship * added `ast::ptr_base::as()` with same semantics as `dynamic_cast(p)` * added `N * ast::ptr_base::set_and_mutate( const N * n )` * takes ownership of `n`, then returns a mutable version owned by this pointer * Some debate on whether this is a good approach: * makes an easy path to cloning, which we were trying to eliminate * counter-point: these are all mutating clones rather than lifetime-preserving clones, and thus "necessary" (for some definition) * existing uses: * `VariableExpr::VariableExpr`, `UntypedExpr::createDeref` * both involve grabbing a type from elsewhere and making an `lvalue` copy of it * could potentially be replaced by a view class something like this: ``` template class AddQualifiersType final : public Type { readonly base; // ... }; ``` * requires all `qualifiers` use (and related helpers) to be virtual, non-zero overhead * also subtle semantic change, where mutations to the source decl now change the viewing expression ## Visitors ## * `Visitor` and `Mutator` are combined into a single `ast::Visitor` class * Base nodes now override `const Node * accept( Visitor & v ) const = 0` with, e.g. `const Stmt * accept( Visitor & v ) const override = 0` * `PassVisitor` is replaced with `ast::Pass` * Most one shot uses can use `ast::Pass::run` and `ast::Pass::read`. `WithConstTypeSubstitution` * `env` => `typeSubs` ## Structural Changes ## `CodeLocation` has been devolved from `BaseSyntaxNode` to `ast::ParseNode` * excludes `ast::Type` from carrying location information * `CodeLocation` is a mandatory constructor field for `ast::ParseNode` * all subclass constructors must fill it; by convention, from their first argument `N->print(std::ostream&)` is a visitor now * `Declaration::printShort` is also integrated `clone` is private to `Node` now * still needs to be overriden to return appropriate type * e.g. `private: virtual Stmt * clone() const override = 0;` * because friendship is not inherited, all implementations of clone need /// Must be copied in ALL derived classes template friend node_t * mutate(const node_t * node); template friend node_t * shallowCopy(const node_t * node); or equilant. * You should use the `mutate` function where possible as it avoids extra copies. * If you must copy use `shallowCopy` or `deepCopy` as required. All leaves of the `Node` inheritance tree are now declared `final` * e.g. `class CompoundStmt final : public Stmt` * allows compiler to optimize virtual calls to static calls if given static type Pulled `FuncSpecifiers`, `StorageClasses`, `CVQualifiers` out of `Type` into their own headers * Made `BFCommon` a `MakeBitfield` macro in its own header * added default and field-init constructors to macro Prefer move semantics for containers passed to node constructors ## Code Style ## ### Files ### * Headers have a `.hpp` suffix * Source code has a `.cpp` suffix * All source has the project-standard leading and trailing comments * prefer `#pragma once` over `#ifdef` guards * namespaces that cover entire files don't get indented * The general node headers only `#include "Fwd.hpp"` if they can get away with it * Anything that needs definitions goes in the .cpp file * `Type.hpp` includes `Decl.hpp` so that it knows the `AggregateDecl` subclasses for `ReferenceToType::aggr()` overloads ### Documentation ### * class, method, and field comments should use doxygen-style `///` prefix * should be included on all classes * should be included on any method declaration that doesn't have an obvious behaviour from either naming convention (e.g. constructor, print operator, implement visitor pattern) or an inline implementation * use explanatory comments with `//` wherever appropriate * older comments should be maintained in porting process wherever possible ### Naming ### * Preserve names from previous AST whenever reasonable, and get team consensus on any changes. * Strong justification required for private fields * No `get_` prefix on getters (including for generated fields) * exception is `DeclWithType::get_type()` * Notable changes: * for concision and consistency with subclasses: * `Declaration` => `ast::Decl` * `DeclarationWithType` => `ast::DeclWithType` * `Expression` => `ast::Expr` * `Initializer` => `ast::Init` * `Statement` => `ast::Stmt` * `ReferenceToType` => `ast::BaseInstType` * any field names should follow a similar renaming * because they don't really belong to `Type` (and for consistency with `Linkage::Spec`): * `Type::StorageClasses` => `ast::Storage::Classes` * `Type::Extern` etc. => `ast::Storage::Extern` etc. * `Type::FuncSpecifiers` => `ast::Function::Specs` * `Type::Inline` etc. => `ast::Function::Inline` etc. * `Type::Qualifiers` => `ast::CV::Qualifiers` * `Type::Const` etc. => `ast::CV::Const` * couldn't break name-dependency loop without pulling `Qualifiers` out of `Type` * `LinkageSpec::Spec` => `ast::Linkage::Spec` * `LinkageSpec::Mangle` etc. => `ast::Linkage::Mangle` etc. * `LinkageSpec::linkageUpdate` => `ast::Linkage::update` * `LinkageSpec::linkageName` => `ast::Linkage::name` * `LinkageSpec::isMangled(Spec)` etc. => `Spec.is_mangled` etc. * `LinkageSpec::Intrinsic` etc. => `ast::Linkage::Intrinsic` etc. * Boolean flags to `SymTab::Mangler::mangle` are now a `SymTab::Mangle::Mode` struct * uses `bitfield` * Because `Indexer` isn't a terribly evocative name: * `SymTab::Indexer` => `ast::SymbolTable` * `SymTab/Indexer.{h,cc}` => `AST/SymbolTable.{hpp,cpp}` * `WithIndexer` => `WithSymbolTable` * `indexer` => `symTab` * `IdData::deleteStmt` => `IdData::deleter` * `lookupId()` now returns a vector rather than an out-param list * To avoid name collisions: * `SymTab::Mangler` => `Mangle` * `ResolvExpr::TypeEnvironment` => `ast::TypeEnvironment` * in `AST/TypeEnvironment.hpp` * Boolean constructor parameters get replaced with a dedicated flag enum: * e.g. `bool isVarLen;` => `enum LengthFlag { FixedLen, VariableLen };` `LengthFlag isVarLen;` * field can be *read* in the existing boolean contexts, but requires documentation to write * suggest naming all flag enums `FooFlag` to hint at boolean nature ## Specific Nodes ## `Attribute` * `parameters` => `params` `Decl` * `storageClasses` => `storage` * `declFromId()` => `fromId()` * not 100% sure about the return type here... `DeclWithType` * When `SymTab::Validate::Pass2` is rewritten, update comment on `mangleName` with new name of pass * `get_scopedMangleName()` => `scopedMangleName()` * `get_type()` now returns `const Type*` so can't be inadvertently mutated * still with `get_` name so it doesn't conflict with subclass field names `ObjectDecl` * changed constructor parameter order for better defaults * allows `newObject` as just default settings `FunctionDecl` * `params` and `returns` added. * Contain the declarations of the parameters and return variables. * Types should match (even be shared with) the fields of `type`. `NamedTypeDecl` * `parameters` => `params` `TypeDecl` * moved `TypeDecl::Kind` to `ast::TypeVar::Kind` `AggregateDecl` * `parameters` => `params` `StructDecl` * `makeInst` replaced by better constructor on `StructInstType`. `Expr` * Merged `inferParams`/`resnSlots` into union, as suggested by comment in old version * does imply get_/set_ API, and some care about moving backward * added constructor that sets result, for benefit of types that set it directly `ApplicationExpr` * `function` => `func` `UntypedExpr` * `function` => `func` * removed `begin_args()` in favour of `args.begin()` `ConstantExpr` * inlined features of `Constant`, never used elsewhere, so removed `Constant` * `Constant Constant::from_int(int)` etc. => `ConstantExpr * ConstantExpr::from_int(CodeLocation, int)` * allocates new `ConstantExpr`, consistent with all existing uses `SizeofExpr`, `AlignofExpr` * `isType` deprecated in favour of boolean check on `type` * all existing uses assume `type` set if true and don't use `expr` `LogicalExpr` * un-defaulted constructor parameter determining `&&` or `||` `CompoundLiteralExpr` * `initializer` => `init` `RangeExpr` * removed `set_low`, `set_high` due to disuse `TupleIndexExpr` * removed `set_tuple`, `set_index` due to disuse `GenericExpr` * `Association::isDefault` removed: `! type` is equivalent `StmtExpr` * `statements` => `stmts` `Init` * `bool maybeConstruct` => `enum ConstructFlag { DoConstruct, MaybeConstruct }` `Label` * `get_statement()` exclusively used for code location, replaced with `CodeLocation` field `CaseStmt` => `CaseClause` * `_isDefault` has been removed * `isDefault` calculates value from `cond` * default may not have a condition. I believe case (!default) requires a condition. `BranchStmt` * `Type` -> `Kind` and `type` -> `kind` * Constructors no longer throw SemanticErrorException: * `label` constructor claims it is now considered a syntax error, replaced with assert. * `computedTarget` constructor assumes `Goto`, other check would have SegFaulted. `TryStmt` * `block` -> `body` and `finallyBlock` -> `finally` `ThrowStmt` and `CatchStmt` => `CatchClause` * moved `Kind` enums to shared `ast::ExceptionKind` enum `FinallyStmt` => `FinallyClause` * `block` -> `body` `CompoundStmt` * Still a `std::list` for children, rather than `std::vector` * allows more-efficient splicing for purposes of later code generation `Type` * `CV::Qualifiers` moved to end of constructor parameter list, defaulted to `{}` * removed getter, setter in favour of public `qualifiers` field * `ReferenceToType` puts a defaulted list of attributes after qualifiers * `forall` field split off into `ParameterizedType` subclass * any type that needs it can inherit from `ParameterizedType` * currently `FunctionType`, `ReferenceToType` * `get_qualifiers()` replaced with accessor `qualifiers()` and mutator `set_qualifiers()` * `get_const()` etc. replaced with `is_const()` etc. variants * `referenceDepth()` now returns `unsigned` rather than `int` * A number of features only supported on aggregates pushed down to `ReferenceToType`: * `attributes`: per docs [1] GCC only supports type attributes on aggregates and typedefs * suggest adding a `TypeWithAttributes` wrapper type if this proves insufficient * `getAggr()` => `aggr()` * also now returns `const AggregateDecl *` * `genericSubstitution()` moved to own visitor in `AST/GenericSubstitution.hpp` * subsumes old `makeGenericSubstitution()` `BasicType` * **TODO** move `kind`, `typeNames` into code generator `ReferenceToType` => `BaseInstType` * deleted `get_baseParameters()` from children * replace with `aggr() ? aggr()->params : nullptr` * `parameters` => `params` * hoisted `lookup` implementation into parent, made non-virtual * also changed to return vector rather than filling; change back if any great win for reuse * `baseStruct` etc. renamed to `base` `PointerType`/`ArrayType` * `is_array()` => `isArray()` * `bool isVarLen;` => `enum LengthFlag { FixedLen, VariableLen }; LengthFlag isVarLen;` * `bool isStatic;` => `enum DimensionFlag { DynamicDim, StaticDim }; DimensionFlag isStatic;` `FunctionType` * `returnVals` => `returns` * `parameters` => `params` * Both now just point at types. * `bool isVarArgs;` => `enum ArgumentFlag { FixedArgs, VariableArgs }; ArgumentFlag isVarArgs;` `SueInstType` * Template class, with specializations and using to implement some other types: * `StructInstType`, `UnionInstType` & `EnumInstType` * `baseStruct`, `baseUnion` & `baseEnum` => `base` `TypeInstType` * `bool isFtype` => `TypeVar::Kind kind` `TypeofType` * `bool is_basetypeof` => `enum Kind { Typeof, Basetypeof } kind;` `TupleType` * removed `value_type` typedef due to likely error * if readded, should be `const Type *` `AttrType` * did not port due to deprecation of feature * feature is `type@thing` e.g. `int@MAX` `referenceToRvalueConversion` * now returns `const Expr *` rather than mutating argument `printAssertionSet`, `printOpenVarSet` * `ostream &` now first argument, for consistency `EqvClass` * `type` => `bound` `TypeEnvironment` * `makeSubstitution()` => `writeToSubstitution()` * `isEmpty()` => `empty()` * removed `clone()` in favour of explicit copies `occurs` * moved to be helper function in `TypeEnvironment.cpp` (its only use) `WidenMode` * changed `widenFirst`, `widenSecond` => `first`, `second` * changed `WidenMode widenMode` => `WidenMode widen` `Alternative` => `Candidate` * `openVars` => `open` `ExplodedActual` => `ExplodedArg` * `ExplodedActual.h` => `ExplodedArg.hpp` `polyCost` * switched order of `env`, `symtab` parameters for better consistency `findMinCost` * pulled out conversion cost promotion into separate `promoteCvtCost` function `resolveAssertions` => `satisfyAssertions` * `ResolveAssertions.h` => `SatisfyAssertions.hpp` * `Resn*` => `Sat*` [1] https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Type-Attributes.html#Type-Attributes