a61fe4177f
In its default compatibility mode, the Ivy template type-checker attempts to
emulate the View Engine default mode as accurately as is possible. This
commit addresses a gap in this compatibility that stems from a View Engine
type-checking bug.
Consider two template expressions:
```html
{{ obj?.field }}
{{ fn()?.field }}
```
and suppose that the type of `obj` and `fn()` are the same - both return
either `null` or an object with a `field` property.
Under View Engine, these type-check differently. The `obj` case will catch
if the object type (when not null) does not have a `field` property, while
the `fn()` case will not. This is due to how View Engine represents safe
navigations:
```typescript
// for the 'obj' case
(obj == null ? null as any : obj.field)
// for the 'fn()' case
let tmp: any;
((tmp = fn()) == null ? null as any : tmp.field)
```
Because View Engine uses the same code generation backend as it does to
produce the runtime code for this expression, it uses a ternary for safe
navigation, with a temporary variable to avoid invoking 'fn()' twice. The
type of this temporary variable is 'any', however, which causes the
`tmp.field` check to be meaningless.
Previously, the Ivy template type-checker in compatibility mode assumed that
`fn()?.field` would always check for the presence of 'field' on the non-null
result of `fn()`. This commit emulates the View Engine bug in Ivy's
compatibility mode, so an 'any' type will be inferred under the same
conditions.
As part of this fix, a new format for safe navigation operations in template
type-checking code is introduced. This is based on the realization that
ternary based narrowing is unnecessary.
For the `fn()` case in strict mode, Ivy now generates:
```typescript
(null as any ? fn()!.field : undefined)
```
This effectively uses the ternary operator as a type "or" operation. The
resulting type will be a union of the type of `fn()!.field` with
`undefined`.
For the `fn()` case in compatibility mode, Ivy now emulates the bug with:
```typescript
(fn() as any).field
```
The cast expression includes the call to `fn()` and allows it to be checked
while still returning a type of `any` from the expression.
For the `obj` case in compatibility mode, Ivy now generates:
```typescript
(obj!.field as any)
```
This cast expression still returns `any` for its type, but will check for
the existence of `field` on the type of `obj!`.
PR Close #35462
|
||
|---|---|---|
| .circleci | ||
| .devcontainer | ||
| .github | ||
| .vscode | ||
| .yarn | ||
| aio | ||
| docs | ||
| integration | ||
| modules | ||
| packages | ||
| scripts | ||
| third_party | ||
| tools | ||
| .bazelignore | ||
| .bazelrc | ||
| .clang-format | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .nvmrc | ||
| .pullapprove.yml | ||
| .yarnrc | ||
| BUILD.bazel | ||
| CHANGELOG.md | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| LICENSE | ||
| README.md | ||
| WORKSPACE | ||
| browser-providers.conf.js | ||
| gulpfile.js | ||
| karma-js.conf.js | ||
| package.json | ||
| protractor-perf.conf.js | ||
| shims_for_IE.js | ||
| test-events.js | ||
| test-main.js | ||
| tslint.json | ||
| yarn.lock | ||
| yarn.lock.readme.md | ||
README.md
Angular
Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages.
Quickstart
Changelog
Learn about the latest improvements.
Want to help?
Want to file a bug, contribute some code, or improve documentation? Excellent! Read up on our guidelines for contributing and then check out one of our issues in the hotlist: community-help.