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* infer from usage's unification uses multiple passes
Previously, the unification step of infer-from-usage codefix would stop
as soon an answer was found. Now it continues if the result is
*incomplete*, with the idea that later passes may provide a better
inference.
Currently, an *incomplete* inference is
1. The type any.
2. The empty object type `{}` or a union or intersection that contains
`{}`.
In the checker, any takes priority over other types since it basically
shuts down type checking. For type inference, however, any is one of the least
useful inferences.
`{}` is not a good inference for a similar reason; as a parameter
inference, it doesn't tell the caller much about what is expected, and
it doesn't allow the function author to use an object as expected. But
currently it's inferred whenever there's an initialisation with the
value `{}`. With this change, subsequent property assignments to the
same parameter will replace the `{}` with a specific anonymous type. For
example:
```js
function C(config) {
if (config === undefined) config = {};
this.x = config.x;
this.y = config.y;
this.z = config.z;
}
```
* Unify all passes of inference from usage
In the previous commit, I changed inference from usage to continue
inference if a the result was *incomplete*. This commit now runs all 4
inference passes and combines them in a unification step. Currently the
unification step is simple, it:
1. Gathers all inferences in a list.
2. Makes properties of anonymous types optional if there is an empty
object in the inference list.
3. Removes *vacuous* inferences.
4. Combines the type in a union.
An inference is *vacuous* if it:
1. Is any or void, when a non-any, non-void type is also inferred.
2. Is the empty object type, when an object type that is not empty is
also inferred.
3. Is an anonymous type, when a non-nullable, non-any, non-void,
non-anonymous type is also inferred.
I think I might eventually want a concept of priorities, like the
compiler's type parameter inference, but I don't have enough examples to
be sure yet.
Eventually, unification should have an additional step that examines the
whole inference list to see if its contents are collectively
meaningless. A good example is `null | undefined`, which is not useful.
* Remove isNumberOrString
* Unify anonymous types
@andy-ms pointed out that my empty object code was a special case of
merging all anonymous types from an inference and making properties
optional that are not in all the anonymous type. So I did that instead.
* Use getTypeOfSymbolAtLocation instead of Symbol.type!
* Unify parameter call-site inferences too
Because they still have a separate code path, they didn't use the new
unification code.
Also some cleanup from PR comments.
* Add object type unification test
Also remove dead code.
* Only use fallback if no inferences were found
Instead of relying on the unification code to remove the fallback.
TypeScript
TypeScript is a language for application-scale JavaScript. TypeScript adds optional types to JavaScript that support tools for large-scale JavaScript applications for any browser, for any host, on any OS. TypeScript compiles to readable, standards-based JavaScript. Try it out at the playground, and stay up to date via our blog and Twitter account.
Installing
For the latest stable version:
npm install -g typescript
For our nightly builds:
npm install -g typescript@next
Contribute
There are many ways to contribute to TypeScript.
- Submit bugs and help us verify fixes as they are checked in.
- Review the source code changes.
- Engage with other TypeScript users and developers on StackOverflow.
- Join the #typescript discussion on Twitter.
- Contribute bug fixes.
- Read the language specification (docx, pdf, md).
This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.
Documentation
Building
In order to build the TypeScript compiler, ensure that you have Git and Node.js installed.
Clone a copy of the repo:
git clone https://github.com/Microsoft/TypeScript.git
Change to the TypeScript directory:
cd TypeScript
Install Jake tools and dev dependencies:
npm install -g jake
npm install
Use one of the following to build and test:
jake local # Build the compiler into built/local
jake clean # Delete the built compiler
jake LKG # Replace the last known good with the built one.
# Bootstrapping step to be executed when the built compiler reaches a stable state.
jake tests # Build the test infrastructure using the built compiler.
jake runtests # Run tests using the built compiler and test infrastructure.
# You can override the host or specify a test for this command.
# Use host=<hostName> or tests=<testPath>.
jake runtests-browser # Runs the tests using the built run.js file. Syntax is jake runtests. Optional
parameters 'host=', 'tests=[regex], reporter=[list|spec|json|<more>]'.
jake baseline-accept # This replaces the baseline test results with the results obtained from jake runtests.
jake lint # Runs tslint on the TypeScript source.
jake help # List the above commands.
Usage
node built/local/tsc.js hello.ts
Roadmap
For details on our planned features and future direction please refer to our roadmap.