source: src/AST/porting.md @ 0e42794

arm-ehjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-expr
Last change on this file since 0e42794 was 0e42794, checked in by Aaron Moss <a3moss@…>, 3 years ago

Rewrite WithSymbolTable? pass accessory to use ast::SymbolTable?

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