Update the typecheck.md page to talk about singleton types and their uses, tagged unions.
As a driveby, improve the documentation on type refinements. And delete the unknown symbols part, this is really dated.
* Update docs/_pages/typecheck.md to fix a typo
Co-authored-by: Arseny Kapoulkine <arseny.kapoulkine@gmail.com>
This is a meta-RFC. I'd like to propose to remove the postfix `!` operator from the language.
I'd like to argue that this operator will eventually become useless and can only be used incorrectly at some point in the future, and that there are likely ways for them to be sound without having to reach for the `!` hammer.
With that, I present these counterarguments:
Shortcoming <span>#</span>1: Refinements does not apply to the block after `return`/`break`/`continue`.
```lua
if not x or not y then return end
-- both x and y are truthy
```
This will be solved by implementing control flow analysis where it'd apply the inverse of the condition leading up to the control transfer statement to the rest of the scope.
Shortcoming <span>#</span>2: Type checker is not aware of the actual state of various locations.
```lua
type Foo = { x: { y: number }? }?
local foo: Foo = { x = { y = 5 } }
print(foo.x.y) -- prints 5 at runtime, type checker warns on this
```
This will be solved by implementing type states where it would inspect the initialization sites as well as assignments to know their actual states. That is, rather than trusting the type annotation `Foo` as the state which gets us far enough, we'd start seeing these type annotations as a subtype constraint for the location `foo`.
---
If there are other use cases not covered in this message, we should talk about that and see if there exists an alternative direction that can solve these use cases soundly.
* Luau Recap: February 2022
* Rebuild pages
* Fixed Markdown linter warnings, converted tabs to spaces and added a note on 'select' optimization
* Apply suggestions from code review
Co-authored-by: Alexander McCord <11488393+alexmccord@users.noreply.github.com>
* Added information about new lint
* Update docs/_posts/2022-02-28-luau-recap-february-2022.md
Co-authored-by: Alexander McCord <11488393+alexmccord@users.noreply.github.com>
Co-authored-by: Alexander McCord <11488393+alexmccord@users.noreply.github.com>
Prototypes booleans and relational operators.
As part of this I removed `FFI/Data/Bool.agda`, because it was getting in the way - we already use `Agda.Builtin.Bool` instead for other cases.
Changed the GHA workflows to:
- Not run `build` and `release` workflows for PRs that only affect `prototyping/`
- Run `prototyping` workflow when PRs affect `Analysis/**`, `Ast/**`, or the `luau-ast` source files
We don't emit type annotations right now for `AstLocal`s in the JSON encoder. This makes it really hard to surface annotations in the Agda implementation. This PR changes it to emit location and type annotations, if present.
Adds a `luau-ast` CLI that dumps Luau source to JSON. @asajeffrey and I are planning to use this functionality to construct an Agda model of the Luau type system/operational semantics, to allow formally proving properties of Luau's type systems.
- Improve refinement support for unions, in particular it's now possible to implement tagged unions as a union of tables where individual branches use a string literal type for one of the fields.
- Fix `string.split` type information
- Optimize `select(_, ...)` to run in constant time (~2.7x faster on VariadicSelect benchmark)
- Improve debug line information for multi-line assignments
- Improve compilation of table literals when table keys are constant expressions/variables
- Use forward GC barrier for `setmetatable` which slightly accelerates GC progress
- TableOperations lint now includes a warning for table.create(N, {}) (which is likely a mistake since the table is shared by all entries)
- Type checker now type checks #v when v is a union
- Parser now rejects sources that consists of a single unfinished long comment
- Work around significant MSVC 2022 performance regression, bringing it more or less in line with MSVC 2019
- Compiler now predicts array size for newly allocated tables when the table is filled in a short loop
- Small improvements in compilation throughput (~2% faster)
- Implement paged sweeper for GC which improves sweep throughput 2-3x and reduces memory consumption by 8 bytes per object (once it is stabilized we will see additional 8 bytes per object of savings)
- Improve Repl Tab completion
- Repl now supports -i (interactive mode to run code in context of a script's environment) and -On (to control optimization flags)
- Rework transaction log used for type checking which should result in more robust type checking internals with fewer bugs
- Reduce the amount of memory consumed by type checker on large module graphs
- Type checker now errors on attempts to change the type of imported module fields
- The return type of newproxy is now any (fixes#296)
- Implement new number printing algorithm (Schubfach) which makes tostring() produce precise (round-trippable) and short decimal output up to 10x faster
- Fix lua_Debug::linedefined to point to the line with the function definition instead of the first statement (fixes#265)
- Fix minor bugs in Tab completion in Repl
- Repl now saves/restores command history in ~/.luau_history
- Upgrade CodeMirror to 5.65
- Enable matching paren highlighting via an addon
- Remove extra buttons and replace clear output with a checkbox
- Highlight error line on parsing/execution error
- Change demo layout to wide to increase available width
This doesn't contain all changes for 507 yet but we might want to do the
Luau 0.507 release a bit earlier to end the year sooner.
Changes:
- Type ascription (::) now permits casts between related types in both directions, allowing to refine or loosen the type (RFC #56)
- Fix type definition for tonumber to return number? since the input string isn't guaranteed to contain a valid number
- Fix type refinements for field access via []
- Many stability fixes for type checker
- Provide extra information in error messages for type mismatches in more cases
- Improve performance of type checking for large unions when union members are string literals
- Add coverage reporting support to Repl (--coverage command line argument) and lua_getcoverage C API
- Work around code signing issues during Makefile builds on macOS
- Improve performance of truthiness checks in some cases, particularly on Apple M1, resulting in 10-25% perf gains on qsort benchmark depending on the CPU/compiler
- Fix support for little-endian systems; IBM s390x here we go!
Attempt to fix coverage builds by using checkout@v2 instead of v1 which might fix the detacthed HEAD issue.
On the off chance it doesn't, add extra logging around git specifically.
* Do not allow regular type assignment to a type pack as a default parameter
* With type pack support in type aliases, this second form with an empty list is now supported
* Update rfcs/syntax-default-type-alias-type-parameters.md
Co-authored-by: Alan Jeffrey <403333+asajeffrey@users.noreply.github.com>
* Update syntax-default-type-alias-type-parameters.md
Even more examples
Co-authored-by: Alan Jeffrey <403333+asajeffrey@users.noreply.github.com>
- Fix some cases where type checking would overflow the native stack
- Improve autocomplete behavior when assigning a partially written function call (not currently exposed through command line tools)
- Improve autocomplete type inference feedback for some expressions where previously the type would not be known
- Improve quantification performance during type checking for large types
- Improve type checking for table literals when the expected type of the table is known because of a type annotation
- Fix type checking errors in cases where required module has errors in the resulting type
- Fix debug line information for multi-line chained call sequences (Add function name information for "attempt to call a nil value" #255)
- lua_newuserdata now takes 2 arguments to match Lua/LuaJIT APIs better; lua_newuserdatatagged should be used if the third argument was non-0.
- lua_ref can no longer be used with LUA_REGISTRYINDEX to prevent mistakes when migrating Lua FFI (Inconsistency with lua_ref #247)
- Fix assertions and possible crashes when executing script code indirectly via metatable dispatch from lua_equal/lua_lessthan/lua_getfield/etc. (Hitting a crash in an assert after lua_equal is called. #259)
- Fix flamegraph scripts to run under Python 2
Alexander McCord