| 1 | # Porting notes for new AST #
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| 2 |
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| 3 | ## Pointer Types ##
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| 4 | * raw pointer `T*` is used for construction, but not storage
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| 5 | * `ast::ptr_base<T,R>` is a pointer to AST node `T` with reference type `R`
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| 6 | * specialization: strong pointer `ast::ptr<T>` is used for an ownership relationship
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| 7 | * specialization: weak pointer `ast::readonly<T>` is used for an observation relationship
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| 8 | * added `ast::ptr_base<T,R>::as<S>()` with same semantics as `dynamic_cast<S*>(p)`
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| 9 | * added `N * ast::ptr_base<N,R>::set_and_mutate( const N * n )`
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| 10 | * takes ownership of `n`, then returns a mutable version owned by this pointer
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| 11 | * Some debate on whether this is a good approach:
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| 12 | * makes an easy path to cloning, which we were trying to eliminate
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| 13 | * counter-point: these are all mutating clones rather than lifetime-preserving clones, and thus "necessary" (for some definition)
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| 14 | * existing uses:
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| 15 | * `VariableExpr::VariableExpr`, `UntypedExpr::createDeref`
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| 16 | * both involve grabbing a type from elsewhere and making an `lvalue` copy of it
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| 17 | * could potentially be replaced by a view class something like this:
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| 18 | ```
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| 19 | template<unsigned Quals>
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| 20 | class AddQualifiersType final : public Type {
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| 21 | readonly<Type> base;
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| 22 | // ...
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| 23 | };
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| 24 | ```
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| 25 | * requires all `qualifiers` use (and related helpers) to be virtual, non-zero overhead
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| 26 | * also subtle semantic change, where mutations to the source decl now change the viewing expression
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| 27 |
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| 28 | ## Visitors ##
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| 29 | * `Visitor` and `Mutator` are combined into a single `ast::Visitor` class
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| 30 | * Base nodes now override `const Node * accept( Visitor & v ) const = 0` with, e.g. `const Stmt * accept( Visitor & v ) const override = 0`
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| 31 | * `PassVisitor` is replaced with `ast::Pass`
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| 32 |
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| 33 | ## Structural Changes ##
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| 34 | `CodeLocation` has been devolved from `BaseSyntaxNode` to `ast::ParseNode`
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| 35 | * excludes `ast::Type` from carrying location information
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| 36 | * `CodeLocation` is a mandatory constructor field for `ast::ParseNode`
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| 37 | * all subclass constructors must fill it; by convention, from their first argument
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| 38 |
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| 39 | `N->print(std::ostream&)` is a visitor now
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| 40 | * `Declaration::printShort` is also integrated
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| 41 |
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| 42 | `clone` is private to `Node` now
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| 43 | * still needs to be overriden to return appropriate type
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| 44 | * e.g. `private: virtual Stmt * clone() const override = 0;`
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| 45 | * because friendship is not inherited, all implementations of clone need
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| 46 | /// Must be copied in ALL derived classes
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| 47 | template<typename node_t>
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| 48 | friend node_t * mutate(const node_t * node);
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| 49 |
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| 50 | All leaves of the `Node` inheritance tree are now declared `final`
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| 51 | * e.g. `class CompoundStmt final : public Stmt`
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| 52 | * allows compiler to optimize virtual calls to static calls if given static type
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| 53 |
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| 54 | Pulled `FuncSpecifiers`, `StorageClasses`, `CVQualifiers` out of `Type` into their own headers
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| 55 | * Made `BFCommon` a `MakeBitfield` macro in its own header
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| 56 | * added default and field-init constructors to macro
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| 57 |
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| 58 | Prefer move semantics for containers passed to node constructors
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| 59 |
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| 60 | ## Code Style ##
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| 61 |
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| 62 | ### Files ###
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| 63 | * Headers have a `.hpp` suffix
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| 64 | * Source code has a `.cpp` suffix
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| 65 | * All source has the project-standard leading and trailing comments
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| 66 | * prefer `#pragma once` over `#ifdef` guards
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| 67 | * namespaces that cover entire files don't get indented
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| 68 | * The general node headers only `#include "Fwd.hpp"` if they can get away with it
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| 69 | * Anything that needs definitions goes in the .cpp file
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| 70 | * `Type.hpp` includes `Decl.hpp` so that it knows the `AggregateDecl` subclasses for `ReferenceToType::aggr()` overloads
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| 71 |
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| 72 | ### Documentation ###
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| 73 | * class, method, and field comments should use doxygen-style `///` prefix
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| 74 | * should be included on all classes
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| 75 | * 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
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| 76 | * use explanatory comments with `//` wherever appropriate
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| 77 | * older comments should be maintained in porting process wherever possible
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| 78 |
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| 79 | ### Naming ###
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| 80 | * Preserve names from previous AST whenever reasonable, and get team consensus on any changes.
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| 81 | * Strong justification required for private fields
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| 82 | * No `get_` prefix on getters (including for generated fields)
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| 83 | * exception is `DeclWithType::get_type()`
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| 84 | * Notable changes:
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| 85 | * for concision and consistency with subclasses:
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| 86 | * `Declaration` => `ast::Decl`
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| 87 | * `DeclarationWithType` => `ast::DeclWithType`
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| 88 | * `Expression` => `ast::Expr`
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| 89 | * `Initializer` => `ast::Init`
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| 90 | * `Statement` => `ast::Stmt`
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| 91 | * any field names should follow a similar renaming
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| 92 | * because they don't really belong to `Type` (and for consistency with `Linkage::Spec`):
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| 93 | * `Type::StorageClasses` => `ast::Storage::Classes`
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| 94 | * `Type::Extern` etc. => `ast::Storage::Extern` etc.
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| 95 | * `Type::FuncSpecifiers` => `ast::Function::Specs`
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| 96 | * `Type::Inline` etc. => `ast::Function::Inline` etc.
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| 97 | * `Type::Qualifiers` => `ast::CV::Qualifiers`
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| 98 | * `Type::Const` etc. => `ast::CV::Const`
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| 99 | * couldn't break name-dependency loop without pulling `Qualifiers` out of `Type`
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| 100 | * `LinkageSpec::Spec` => `ast::Linkage::Spec`
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| 101 | * `LinkageSpec::Mangle` etc. => `ast::Linkage::Mangle` etc.
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| 102 | * `LinkageSpec::linkageUpdate` => `ast::Linkage::update`
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| 103 | * `LinkageSpec::linkageName` => `ast::Linkage::name`
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| 104 | * `LinkageSpec::isMangled(Spec)` etc. => `Spec.is_mangled` etc.
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| 105 | * `LinkageSpec::Intrinsic` etc. => `ast::Linkage::Intrinsic` etc.
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| 106 | * Boolean flags to `SymTab::Mangler::mangle` are now a `SymTab::Mangle::Mode` struct
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| 107 | * uses `bitfield`
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| 108 | * Because `Indexer` isn't a terribly evocative name:
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| 109 | * `SymTab::Indexer` => `ast::SymbolTable`
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| 110 | * `SymTab/Indexer.{h,cc}` => `AST/SymbolTable.{hpp,cpp}`
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| 111 | * `WithIndexer` => `WithSymbolTable`
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| 112 | * `indexer` => `symTab`
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| 113 | * `IdData::deleteStmt` => `IdData::deleter`
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| 114 | * `lookupId()` now returns a vector rather than an out-param list
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| 115 | * To avoid name collisions:
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| 116 | * `SymTab::Mangler` => `Mangle`
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| 117 | * `ResolvExpr::TypeEnvironment` => `ast::TypeEnvironment`
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| 118 | * in `AST/TypeEnvironment.hpp`
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| 119 | * Boolean constructor parameters get replaced with a dedicated flag enum:
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| 120 | * e.g. `bool isVarLen;` => `enum LengthFlag { FixedLen, VariableLen };` `LengthFlag isVarLen;`
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| 121 | * field can be *read* in the existing boolean contexts, but requires documentation to write
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| 122 | * suggest naming all flag enums `FooFlag` to hint at boolean nature
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| 123 |
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| 124 | ## Specific Nodes ##
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| 125 | `Attribute`
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| 126 | * `parameters` => `params`
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| 127 |
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| 128 | `Decl`
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| 129 | * `storageClasses` => `storage`
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| 130 | * `declFromId()` => `fromId()`
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| 131 | * not 100% sure about the return type here...
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| 132 |
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| 133 | `DeclWithType`
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| 134 | * When `SymTab::Validate::Pass2` is rewritten, update comment on `mangleName` with new name of pass
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| 135 | * `get_scopedMangleName()` => `scopedMangleName()`
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| 136 | * `get_type()` now returns `const Type*` so can't be inadvertently mutated
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| 137 | * still with `get_` name so it doesn't conflict with subclass field names
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| 138 |
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| 139 | `ObjectDecl`
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| 140 | * changed constructor parameter order for better defaults
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| 141 | * allows `newObject` as just default settings
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| 142 |
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| 143 | `NamedTypeDecl`
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| 144 | * `parameters` => `params`
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| 145 |
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| 146 | `TypeDecl`
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| 147 | * moved `TypeDecl::Kind` to `ast::TypeVar::Kind`
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| 148 |
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| 149 | `AggregateDecl`
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| 150 | * `parameters` => `params`
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| 151 |
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| 152 | `Expr`
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| 153 | * Merged `inferParams`/`resnSlots` into union, as suggested by comment in old version
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| 154 | * does imply get_/set_ API, and some care about moving backward
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| 155 | * added constructor that sets result, for benefit of types that set it directly
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| 156 |
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| 157 | `ApplicationExpr`
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| 158 | * `function` => `func`
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| 159 |
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| 160 | `UntypedExpr`
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| 161 | * `function` => `func`
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| 162 | * removed `begin_args()` in favour of `args.begin()`
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| 163 |
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| 164 | `ConstantExpr`
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| 165 | * inlined features of `Constant`, never used elsewhere, so removed `Constant`
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| 166 | * `Constant Constant::from_int(int)` etc. => `ConstantExpr * ConstantExpr::from_int(CodeLocation, int)`
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| 167 | * allocates new `ConstantExpr`, consistent with all existing uses
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| 168 |
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| 169 | `SizeofExpr`, `AlignofExpr`
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| 170 | * `isType` deprecated in favour of boolean check on `type`
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| 171 | * all existing uses assume `type` set if true and don't use `expr`
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| 172 |
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| 173 | `AttrExpr`
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| 174 | * did not port due to feature deprecation (e.g. `expr@attribute`)
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| 175 |
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| 176 | `LogicalExpr`
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| 177 | * un-defaulted constructor parameter determining `&&` or `||`
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| 178 |
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| 179 | `CompoundLiteralExpr`
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| 180 | * `initializer` => `init`
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| 181 |
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| 182 | `RangeExpr`
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| 183 | * removed `set_low`, `set_high` due to disuse
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| 184 |
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| 185 | `TupleIndexExpr`
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| 186 | * removed `set_tuple`, `set_index` due to disuse
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| 187 |
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| 188 | `GenericExpr`
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| 189 | * `Association::isDefault` removed: `! type` is equivalent
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| 190 |
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| 191 | `StmtExpr`
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| 192 | * `statements` => `stmts`
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| 193 |
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| 194 | `Init`
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| 195 | * `bool maybeConstruct` => `enum ConstructFlag { DoConstruct, MaybeConstruct }`
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| 196 |
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| 197 | `Label`
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| 198 | * `get_statement()` exclusively used for code location, replaced with `CodeLocation` field
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| 199 |
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| 200 | `CaseStmt`
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| 201 | * `_isDefault` has been removed
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| 202 | * `isDefault` calculates value from `cond`
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| 203 | * default may not have a condition. I believe case (!default) requires a condition.
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| 204 |
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| 205 | `BranchStmt`
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| 206 | * `Type` -> `Kind` and `type` -> `kind`
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| 207 | * Constructors no longer throw SemanticErrorException:
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| 208 | * `label` constructor claims it is now considered a syntax error, replaced with assert.
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| 209 | * `computedTarget` constructor assumes `Goto`, other check would have SegFaulted.
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| 210 |
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| 211 | `TryStmt`
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| 212 | * `block` -> `body` and `finallyBlock` -> `finally`
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| 213 |
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| 214 | `ThrowStmt` `CatchStmt`
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| 215 | * moved `Kind` enums to shared `ast::ExceptionKind` enum
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| 216 |
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| 217 | `FinallyStmt`
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| 218 | * `block` -> `body`
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| 219 |
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| 220 | `CompoundStmt`
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| 221 | * Still a `std::list` for children, rather than `std::vector`
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| 222 | * allows more-efficient splicing for purposes of later code generation
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| 223 |
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| 224 | `Type`
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| 225 | * `CV::Qualifiers` moved to end of constructor parameter list, defaulted to `{}`
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| 226 | * removed getter, setter in favour of public `qualifiers` field
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| 227 | * `ReferenceToType` puts a defaulted list of attributes after qualifiers
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| 228 | * `forall` field split off into `ParameterizedType` subclass
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| 229 | * any type that needs it can inherit from `ParameterizedType`
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| 230 | * currently `FunctionType`, `ReferenceToType`
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| 231 | * `get_qualifiers()` replaced with accessor `qualifiers()` and mutator `set_qualifiers()`
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| 232 | * `get_const()` etc. replaced with `is_const()` etc. variants
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| 233 | * `referenceDepth()` now returns `unsigned` rather than `int`
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| 234 | * A number of features only supported on aggregates pushed down to `ReferenceToType`:
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| 235 | * `attributes`: per docs [1] GCC only supports type attributes on aggregates and typedefs
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| 236 | * suggest adding a `TypeWithAttributes` wrapper type if this proves insufficient
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| 237 | * `getAggr()` => `aggr()`
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| 238 | * also now returns `const AggregateDecl *`
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| 239 | * `genericSubstitution()` moved to own visitor in `AST/GenericSubstitution.hpp`
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| 240 | * subsumes old `makeGenericSubstitution()`
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| 241 |
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| 242 | `BasicType`
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| 243 | * **TODO** move `kind`, `typeNames` into code generator
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| 244 |
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| 245 | `ReferenceToType`
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| 246 | * deleted `get_baseParameters()` from children
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| 247 | * replace with `aggr() ? aggr()->params : nullptr`
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| 248 | * `parameters` => `params`
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| 249 | * hoisted `lookup` implementation into parent, made non-virtual
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| 250 | * also changed to return vector rather than filling; change back if any great win for reuse
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| 251 | * `baseStruct` etc. renamed to `base`
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| 252 |
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| 253 | `PointerType`/`ArrayType`
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| 254 | * `is_array()` => `isArray()`
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| 255 | * `bool isVarLen;` => `enum LengthFlag { FixedLen, VariableLen }; LengthFlag isVarLen;`
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| 256 | * `bool isStatic;` => `enum DimensionFlag { DynamicDim, StaticDim }; DimensionFlag isStatic;`
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| 257 |
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| 258 | `FunctionType`
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| 259 | * `returnVals` => `returns`
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| 260 | * `parameters` => `params`
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| 261 | * `bool isVarArgs;` => `enum ArgumentFlag { FixedArgs, VariableArgs }; ArgumentFlag isVarArgs;`
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| 262 |
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| 263 | `TypeInstType`
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| 264 | * `bool isFtype` => `TypeVar::Kind kind`
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| 265 |
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| 266 | `TypeofType`
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| 267 | * `bool is_basetypeof` => `enum Kind { Typeof, Basetypeof } kind;`
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| 268 |
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| 269 | `TupleType`
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| 270 | * removed `value_type` typedef due to likely error
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| 271 | * if readded, should be `const Type *`
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| 272 |
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| 273 | `AttrType`
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| 274 | * did not port due to deprecation of feature
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| 275 | * feature is `type@thing` e.g. `int@MAX`
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| 276 |
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| 277 | `referenceToRvalueConversion`
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| 278 | * now returns `const Expr *` rather than mutating argument
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| 279 |
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| 280 | `printAssertionSet`, `printOpenVarSet`
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| 281 | * `ostream &` now first argument, for consistency
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| 282 |
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| 283 | `EqvClass`
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| 284 | * `type` => `bound`
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| 285 |
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| 286 | `TypeEnvironment`
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| 287 | * `makeSubstitution()` => `writeToSubstitution()`
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| 288 | * `isEmpty()` => `empty()`
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| 289 | * removed `clone()` in favour of explicit copies
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| 290 |
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| 291 | `occurs`
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| 292 | * moved to be helper function in `TypeEnvironment.cpp` (its only use)
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| 293 |
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| 294 | `WidenMode`
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| 295 | * changed `widenFirst`, `widenSecond` => `first`, `second`
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| 296 | * changed `WidenMode widenMode` => `WidenMode widen`
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| 297 |
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| 298 | `Alternative` => `Candidate`
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| 299 | * `openVars` => `open`
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| 300 |
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| 301 | [1] https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Type-Attributes.html#Type-Attributes
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| 302 |
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