distinct types: nominal newtype over workhorse types — typedef distinct Foo = int

[borisbat]

Promotes weak types (int, float, void?, any workhorse type) to unique nominal types with zero runtime/ABI cost:

typedef distinct EntityId = int
typedef distinct Meters = float
typedef distinct FileHandle = void?

From the ABI perspective a distinct type IS its underlying type — same size, alignment, pass-by-value. But it never interconverts: functions taking int won't take EntityId and vice versa, two distincts over the same underlying are mutually incompatible, and overloads on all of them coexist.

Semantics

• In: Foo(expr) — exactly one argument of exactly the underlying type; a reinterpret relabel, zero runtime cost. var a : Foo = 5 is an error; var a : Foo / default<Foo> zero-init (string/pointer/vector underlyings included).
• Out: *a — peels exactly one distinct level, yields the underlying as a reference (*a = 5 writes; const flows from the handle per the const model). For distinct-over-pointer, * peels the distinct, not the pointer.
• Operators: only ==/!= are borrowed (language-level, same-distinct-only, lowered to a compare of the underlyings at infer). Everything else is user-defined: def operator + (a, b : Meters) : Meters => Meters(*a + *b).
• Not a table key (explicit rejection — the nominal wall is the point). Arrays, struct/tuple/variant fields all work.
• Module-nominal with typedef private distinct Foo = int visibility, like enums.
• Underlying must be a workhorse type; distinct-of-distinct rejected.

Implementation

• distinct is not a keyword at all. The declaration is a distinct_alias production under typedef: typedef [private|public] distinct Foo = int, with distinct a plain NAME validated in the action (Nim's type Foo = distinct int shape). No lexer involvement — comments between tokens lex away normally and every identifier use of distinct (daslib/linq's function etc.) is untouched. Gen2 only; %expect 0 holds. The tree-sitter grammar gets the matching typedef_declaration alternative (parser.c regenerated — one-time large mechanical diff, standing parser.c was tree-sitter-cli 0.22 output, regen is 0.26.9 per the Node-24 requirement; precedent tree-sitter: fix type<T>; parse failure in type position #2877).
• New Type::tDistinct, AST-only, appended after tFixedArray (append-only keeps serialized ordinals/hashes stable). Entity is DistinctTypeAnnotation : TypeAnnotation riding the existing TypeDecl::annotation slot (already cloned/GC-walked/compared/serialized); firstType holds the underlying. ABI predicates (size/align/pod/copy/move/local/workhorse/gc-flags/string-data) delegate to firstType; semantic predicates stay false so nothing leaks.
• Runtime erasure at the makeTypeInfo boundary (same as the fixed-array flatten): interpreter, RTTI, and fusion never observe tDistinct. The JIT walks AST types, so it peels in type_to_llvm_type / type_to_llvm_abi_type / vec4f marshaling and treats the distinct deref as a pass-through (LLVM_JIT_CODEGEN_VERSION bumped). AOT emits the underlying C++ type (DAS_COMMENT(distinct Name) annotated), both in describeCppTypeEx and daslib/aot_cpp.das.
• New mangling char Q<module::name> (emit + parse) keeps f(Foo) / f(int) overloads and AOT hashes distinct.
• Construction rides the aliasSubstitution-style rail: unresolved ExprCall named like a distinct type → ExprCast with reinterpret. Foo() and Foo(a=1) are rejected. The workhorse make-struct fold's Program::makeConst null-deref (pre-existing for any non-const-able type) is fixed; distinct default<> routes string/pointer underlyings like the non-distinct paths and errors cleanly on anything makeConst can't produce.
• Serialization: TypeDecl tDistinct case + das-declared entities round-trip with the module, registered before aliasTypes/enumerations deserialize; own-module annotation references stream by name (serializeAnnotationPointer previously asserted macroContext — das-declared distincts are the first annotations owned by a non-macro module). Version 98 → 99. Exercised by CI's ser/deser sweep (full-tree --ser/--deser green locally).
• C++ side: DistinctTypeAnnotation + MAKE_DISTINCT_TYPE_FACTORY + ModuleLibrary::makeDistinctType let a C++ module register a distinct type and bind externs whose signatures carry it. Worked example: NativeId in dasUnitTest.
• New errors: invalid_distinct_type = 30297, mismatching_distinct_type = 30413.

Validation

• tests/language/test_distinct.das (26 subtests: construct/deref/write, equality, Foo-vs-Bar nominal walls, string/pointer/float3 underlyings incl. default<>, user operators, overload coexistence, containers + struct/tuple/variant fields, generics + is_distinct trait + typedecl(*x), cross-module + fixture) — green under interpreter, JIT, AOT, and ser/deser.
• tests/language/test_distinct_interop.das — C++-registered distinct end-to-end.
• tests/typer_errors/failed_distinct_*.das — declaration, mismatch (incl. cross-distinct), ctor, table-key, private rejections with exact expect codes.
• Full sweep: 11315 tests green interpreted and under test_aot; tree-sitter corpus 42/42.
• Docs: doc/source/reference/language/distinct.rst + rtti Type enum handmade line; das2rst/Sphinx (html + latex -W) clean; preflight full-pass token + sequence smoke green.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a new nominal distinct type feature to daScript (Gen2) that allows creating zero-cost newtypes over “workhorse” value types (e.g. distinct Id = int), with explicit in/out via Foo(x) and *foo, nominal overload separation, and runtime erasure to the underlying ABI type across interpreter/JIT/AOT/RTTI.

Changes:

• Introduces Type::tDistinct + DistinctTypeAnnotation, integrates it into type checking/inference, operator handling (==/!=), mangling, and table-key rejection.
• Extends the Gen2 lexer/parser to recognize distinct declarations as a contextual keyword and build the corresponding AST annotations/types.
• Adds cross-tier support (AST serialization, debug info/typeinfo erasure, LLVM JIT + AOT C++ emission) plus tests and documentation.

Reviewed changes

Copilot reviewed 45 out of 46 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/typer_errors/failed_distinct_table_key.das	New negative test: distinct types rejected as table keys.
tests/typer_errors/failed_distinct_private.das	New negative test: private distinct visibility across modules.
tests/typer_errors/failed_distinct_mismatch.das	New negative test: no implicit interop with underlying / no borrowed ops.
tests/typer_errors/failed_distinct_decl.das	New negative test: distinct-of-distinct and non-workhorse underlying rejected.
tests/typer_errors/failed_distinct_ctor.das	New negative test: ctor arity/type and “no fields” behavior.
tests/language/test_distinct.das	New language-level coverage for construction/deref/equality/containers/generics/modules.
tests/language/test_distinct_interop.das	New interop test for C++-registered distinct types.
tests/language/_distinct_fixture.das	Shared fixture module defining public/private distinct types for cross-module tests.
tests/aot/CMakeLists.txt	Ensures distinct fixture module is included in AOT language test module set.
src/simulate/debug_info.cpp	Adds “distinct” label for debug type name mapping.
src/parser/parser_impl.h	Declares ast_distinctDeclaration parser helper.
src/parser/parser_impl.cpp	Implements distinct declaration validation + registers DistinctTypeAnnotation.
src/parser/lex2.yy.h	Regenerated lexer header line mapping update.
src/parser/ds2_parser.ypp	Adds distinct token and grammar rule for distinct declarations.
src/parser/ds2_parser.hpp	Regenerated parser token enum includes DAS_DISTINCT.
src/parser/ds2_lexer.lpp	Adds contextual lexer rule for distinct ... = to return DAS_DISTINCT.
src/parser/ds2_lexer.cpp	Regenerated lexer tables/code for the new distinct rule.
src/builtin/module_builtin_rtti.h	Exposes Type.tDistinct in RTTI enum binding.
src/builtin/module_builtin_ast_serialize.cpp	Serializes tDistinct TypeDecl + round-trips das-declared distinct annotations in modules.
src/ast/ast_typedecl.cpp	TypeDecl behavior updates for tDistinct (describe, hashing/mangling, ABI delegation, etc.).
src/ast/ast_simulate.cpp	Interpreter simulation: treat *distinct as compile-time relabel (no null-check/deref).
src/ast/ast_program.cpp	Type resolution for distinct annotations + makeConst peels distinct to underlying.
src/ast/ast_module.cpp	Adds ModuleLibrary::makeDistinctType for C++ type-factory integration.
src/ast/ast_infer_type.cpp	Type inference for *distinct, Foo(expr) construction rewrite, and is_distinct trait.
src/ast/ast_infer_type_op.cpp	Lowers ==/!= on same distinct type to underlying compare via deref nodes.
src/ast/ast_infer_type_make.cpp	Special-cases default<distinct> folding (currently problematic for non-numeric underlyings).
src/ast/ast_infer_type_helper.cpp	Verifies distinct validity + rejects distinct table keys with specific error.
src/ast/ast_infer_type_function.cpp	Avoids duplicate/incorrect diagnostics for distinct construction path.
src/ast/ast_debug_info_helper.cpp	Erases tDistinct at AST→TypeInfo boundary (like fixed-array flatten).
modules/dasUnitTest/unitTest.h	Adds C++ NativeId wrapper + cast/WrapType for distinct interop.
modules/dasUnitTest/test_handles.cpp	Registers NativeId as a distinct annotation + binds extern native_id_next.
modules/dasLLVM/daslib/llvm_jit.das	JIT visitor: treat *distinct as relabel and adjust vec4f marshaling.
modules/dasLLVM/daslib/llvm_jit_run.das	Bumps LLVM_JIT_CODEGEN_VERSION for distinct support.
modules/dasLLVM/daslib/llvm_jit_common.das	Erases distinct to underlying in LLVM type mapping (ABI/type).
include/daScript/simulate/debug_info.h	Adds tDistinct to Type enum docs (AST-only + erasure notes).
include/daScript/ast/compilation_errors.h	Adds new error codes for distinct invalidity/mismatch.
include/daScript/ast/ast.h	Adds RTTI hook for distinct annotations + makeDistinctType API on ModuleLibrary.
include/daScript/ast/ast_typefactory.h	Adds MAKE_DISTINCT_TYPE_FACTORY for C++ signature typing.
include/daScript/ast/ast_typedecl.h	Adds TypeDecl::isDistinct() and makeDistinctType declaration.
include/daScript/ast/ast_serializer.h	Bumps AST serializer version for distinct support.
include/daScript/ast/ast_handle.h	Defines DistinctTypeAnnotation (nominal distinct entity).
doc/source/stdlib/handmade/enumeration-rtti-Type.rst	Updates RTTI Type enum docs to include distinct.
doc/source/reference/language/distinct.rst	New language reference page for distinct types (semantics + examples).
doc/source/reference/language.rst	Adds distinct page to language reference TOC.
daslib/aot_cpp.das	AOT: emits underlying C++ type with distinct comment + handles *distinct as relabel.

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[Copilot]

Pull request overview

Copilot reviewed 45 out of 46 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 45 out of 47 changed files in this pull request and generated 1 comment.