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feat(compiler): narrow types of expressions used in *ngIf (#20702)

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Structural directives can now specify a type guard that describes
what types can be inferred for an input expression inside the
directive's template.

NgIf was modified to declare an input guard on ngIf.

After this change, `fullTemplateTypeCheck` will infer that
usage of `ngIf` expression inside it's template is truthy.

For example, if a component has a property `person?: Person`
and a template of `<div *ngIf="person"> {{person.name}} </div>`
the compiler will no longer report that `person` might be null or
undefined.

The template compiler will generate code similar to,

```
  if (NgIf.ngIfTypeGuard(instance.person)) {
    instance.person.name
  }
```

to validate the template's use of the interpolation expression.
Calling the type guard in this fashion allows TypeScript to infer
that `person` is non-null.

Fixes: #19756?

PR Close #20702
This commit is contained in:
Chuck Jazdzewski
2017-11-29 16:29:05 -08:00
committed by Jason Aden
parent e544742156
commit e7d9cb3e4c
19 changed files with 341 additions and 53 deletions
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4
packages/compiler/src/view_compiler/view_compiler.ts
View File

@ -8,7 +8,7 @@
import {CompileDirectiveMetadata, CompilePipeSummary, rendererTypeName, tokenReference, viewClassName} from '../compile_metadata';
import {CompileReflector} from '../compile_reflector';
import {BuiltinConverter, EventHandlerVars, LocalResolver, convertActionBinding, convertPropertyBinding, convertPropertyBindingBuiltins} from '../compiler_util/expression_converter';
import {BindingForm, BuiltinConverter, EventHandlerVars, LocalResolver, convertActionBinding, convertPropertyBinding, convertPropertyBindingBuiltins} from '../compiler_util/expression_converter';
import {ArgumentType, BindingFlags, ChangeDetectionStrategy, NodeFlags, QueryBindingType, QueryValueType, ViewFlags} from '../core';
import {AST, ASTWithSource, Interpolation} from '../expression_parser/ast';
import {Identifiers} from '../identifiers';
@ -859,7 +859,7 @@ class ViewBuilder implements TemplateAstVisitor, LocalResolver {
const bindingId = `${updateBindingCount++}`;
const nameResolver = context === COMP_VAR ? self : null;
const {stmts, currValExpr} =
convertPropertyBinding(nameResolver, context, value, bindingId);
convertPropertyBinding(nameResolver, context, value, bindingId, BindingForm.General);
updateStmts.push(...stmts.map(
(stmt: o.Statement) => o.applySourceSpanToStatementIfNeeded(stmt, sourceSpan)));
return o.applySourceSpanToExpressionIfNeeded(currValExpr, sourceSpan);