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
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| .. | ||
| animations | ||
| bazel | ||
| benchpress | ||
| common | ||
| compiler | ||
| compiler-cli | ||
| core | ||
| docs | ||
| elements | ||
| examples | ||
| forms | ||
| http | ||
| language-service | ||
| localize | ||
| platform-browser | ||
| platform-browser-dynamic | ||
| platform-server | ||
| platform-webworker | ||
| platform-webworker-dynamic | ||
| private/testing | ||
| router | ||
| service-worker | ||
| upgrade | ||
| zone.js | ||
| BUILD.bazel | ||
| README.md | ||
| empty.ts | ||
| goog.d.ts | ||
| license-banner.txt | ||
| system.d.ts | ||
| tsconfig-build-no-strict.json | ||
| tsconfig-build.json | ||
| tsconfig-test.json | ||
| tsconfig.json | ||
| types.d.ts | ||
README.md
Angular
The sources for this package are in the main Angular repo. Please file issues and pull requests against that repo.
Usage information and reference details can be found in Angular documentation.
License: MIT