refactor(language-service): adds Symbol#typeArguments and does cleanup (#34571)

Adds a `typeArguments` method to the `Symbol` interface, cleaning up how
type parameters of a TypeScript type are currently found. This will be
necessary for providing completions for `$event` variables' properties
(#34570).

This commit also performs some fly-by cleanups seen while implementing
the `typeArguments` methods. There is more clean up to do in the
`typescript_symbols` file, but the scope of this commit didn't need to
get larger.

PR Close #34571

packages/language-service/src/expression_type.ts

@@ -223,7 +223,8 @@ export class AstType implements AstVisitor {
       members(): SymbolTable{return _this.scope;},
       signatures(): Signature[]{return [];},
       selectSignature(types): Signature | undefined{return undefined;},
-      indexed(argument): Symbol | undefined{return undefined;}
+      indexed(argument): Symbol | undefined{return undefined;},
+      typeArguments(): Symbol[] | undefined{return undefined;},
     };
   }
 

packages/language-service/src/global_symbols.ts

@@ -59,6 +59,7 @@ export const createGlobalSymbolTable: (query: ng.SymbolQuery) => ng.SymbolTable
             };
           },
           indexed: () => undefined,
+          typeArguments: () => undefined,
         },
       },
     ]);

packages/language-service/src/locate_symbol.ts

@@ -223,4 +223,6 @@ class OverrideKindSymbol implements Symbol {
   selectSignature(types: Symbol[]) { return this.sym.selectSignature(types); }
 
   indexed(argument: Symbol) { return this.sym.indexed(argument); }
+
+  typeArguments(): Symbol[]|undefined { return this.sym.typeArguments(); }
 }

packages/language-service/src/symbols.ts

@@ -129,6 +129,11 @@ export interface Symbol {
    * If the symbol cannot be indexed, this method should return `undefined`.
    */
   indexed(argument: Symbol, key?: any): Symbol|undefined;
+
+  /**
+   * Returns the type arguments of a Symbol, if any.
+   */
+  typeArguments(): Symbol[]|undefined;
 }
 
 /**

packages/language-service/src/typescript_symbols.ts

@@ -125,10 +125,10 @@ class TypeScriptSymbolQuery implements SymbolQuery {
 
   getElementType(type: Symbol): Symbol|undefined {
     if (type instanceof TypeWrapper) {
-      const elementType = getTypeParameterOf(type.tsType, 'Array');
-      if (elementType) {
-        return new TypeWrapper(elementType, type.context);
-      }
+      const tSymbol = type.tsType.symbol;
+      const tArgs = type.typeArguments();
+      if (!tSymbol || tSymbol.name !== 'Array' || !tArgs || tArgs.length != 1) return;
+      return tArgs[0];
     }
   }
 
@@ -206,11 +206,12 @@ class TypeScriptSymbolQuery implements SymbolQuery {
   }
 
   private getTsTypeOf(symbol: Symbol): ts.Type|undefined {
-    const type = this.getTypeWrapper(symbol);
+    const type = getTypeWrapper(symbol);
     return type && type.tsType;
   }
+}
 
-  private getTypeWrapper(symbol: Symbol): TypeWrapper|undefined {
+function getTypeWrapper(symbol: Symbol): TypeWrapper|undefined {
   let type: TypeWrapper|undefined = undefined;
   if (symbol instanceof TypeWrapper) {
     type = symbol;
@@ -219,7 +220,6 @@ class TypeScriptSymbolQuery implements SymbolQuery {
   }
   return type;
 }
-}
 
 function typeCallable(type: ts.Type): boolean {
   const signatures = type.getCallSignatures();
@@ -290,8 +290,8 @@ class TypeWrapper implements Symbol {
   }
 
   indexed(argument: Symbol, value: any): Symbol|undefined {
-    const type = argument instanceof TypeWrapper ? argument : argument.type;
-    if (!(type instanceof TypeWrapper)) return;
+    const type = getTypeWrapper(argument);
+    if (!type) return;
 
     const typeKind = typeKindOf(type.tsType);
     switch (typeKind) {
@@ -311,6 +311,13 @@ class TypeWrapper implements Symbol {
         return sType && new TypeWrapper(sType, this.context);
     }
   }
+
+  typeArguments(): Symbol[]|undefined {
+    // TODO: use checker.getTypeArguments when TS 3.7 lands in the monorepo.
+    const typeArguments: ReadonlyArray<ts.Type> = (this.tsType as any).typeArguments;
+    if (!typeArguments) return undefined;
+    return typeArguments.map(ta => new TypeWrapper(ta, this.context));
+  }
 }
 
 // If stringIndexType a primitive type(e.g. 'string'), the Symbol is undefined;
@@ -342,7 +349,7 @@ class SymbolWrapper implements Symbol {
 
   get kind(): DeclarationKind { return this.callable ? 'method' : 'property'; }
 
-  get type(): Symbol|undefined { return new TypeWrapper(this.tsType, this.context); }
+  get type(): TypeWrapper { return new TypeWrapper(this.tsType, this.context); }
 
   get container(): Symbol|undefined { return getContainerOf(this.symbol, this.context); }
 
@@ -380,6 +387,8 @@ class SymbolWrapper implements Symbol {
 
   indexed(argument: Symbol): Symbol|undefined { return undefined; }
 
+  typeArguments(): Symbol[]|undefined { return this.type.typeArguments(); }
+
   private get tsType(): ts.Type {
     let type = this._tsType;
     if (!type) {
@@ -405,21 +414,21 @@ class DeclaredSymbol implements Symbol {
 
   get container(): Symbol|undefined { return undefined; }
 
-  get type() { return this.declaration.type; }
+  get type(): Symbol { return this.declaration.type; }
 
-  get callable(): boolean { return this.declaration.type.callable; }
+  get callable(): boolean { return this.type.callable; }
 
   get definition(): Definition { return this.declaration.definition; }
 
   get documentation(): ts.SymbolDisplayPart[] { return this.declaration.type.documentation; }
 
-  members(): SymbolTable { return this.declaration.type.members(); }
+  members(): SymbolTable { return this.type.members(); }
 
-  signatures(): Signature[] { return this.declaration.type.signatures(); }
+  signatures(): Signature[] { return this.type.signatures(); }
 
-  selectSignature(types: Symbol[]): Signature|undefined {
-    return this.declaration.type.selectSignature(types);
-  }
+  selectSignature(types: Symbol[]): Signature|undefined { return this.type.selectSignature(types); }
+
+  typeArguments(): Symbol[]|undefined { return this.type.typeArguments(); }
 
   indexed(argument: Symbol): Symbol|undefined { return undefined; }
 }
@@ -442,17 +451,14 @@ class SignatureResultOverride implements Signature {
   get result(): Symbol { return this.resultType; }
 }
 
-export function toSymbolTableFactory(symbols: ts.Symbol[]) {
+export function toSymbolTableFactory(symbols: ts.Symbol[]): ts.SymbolTable {
   // ∀ Typescript version >= 2.2, `SymbolTable` is implemented as an ES6 `Map`
   const result = new Map<string, ts.Symbol>();
   for (const symbol of symbols) {
     result.set(symbol.name, symbol);
   }
-  // First, tell the compiler that `result` is of type `any`. Then, use a second type assertion
-  // to `ts.SymbolTable`.
-  // Otherwise, `Map<string, ts.Symbol>` and `ts.SymbolTable` will be considered as incompatible
-  // types by the compiler
-  return <ts.SymbolTable>(<any>result);
+
+  return result as ts.SymbolTable;
 }
 
 function toSymbols(symbolTable: ts.SymbolTable | undefined): ts.Symbol[] {
@@ -602,7 +608,7 @@ class PipeSymbol implements Symbol {
 
   get name(): string { return this.pipe.name; }
 
-  get type(): Symbol|undefined { return new TypeWrapper(this.tsType, this.context); }
+  get type(): TypeWrapper { return new TypeWrapper(this.tsType, this.context); }
 
   get definition(): Definition|undefined {
     const symbol = this.tsType.getSymbol();
@@ -625,24 +631,21 @@ class PipeSymbol implements Symbol {
     let signature = selectSignature(this.tsType, this.context, types) !;
     if (types.length > 0) {
       const parameterType = types[0];
-      if (parameterType instanceof TypeWrapper) {
-        let resultType: ts.Type|undefined = undefined;
+      let resultType: Symbol|undefined = undefined;
       switch (this.name) {
         case 'async':
-            // Get symbol of 'Observable', 'Promise', or 'EventEmitter' type.
-            const symbol = parameterType.tsType.symbol;
-            if (symbol) {
-              resultType = getTypeParameterOf(parameterType.tsType, symbol.name);
+          // Get type argument of 'Observable', 'Promise', or 'EventEmitter'.
+          const tArgs = parameterType.typeArguments();
+          if (tArgs && tArgs.length === 1) {
+            resultType = tArgs[0];
           }
           break;
         case 'slice':
-            resultType = parameterType.tsType;
+          resultType = parameterType;
           break;
       }
       if (resultType) {
-          signature = new SignatureResultOverride(
-              signature, new TypeWrapper(resultType, parameterType.context));
-        }
+        signature = new SignatureResultOverride(signature, resultType);
       }
     }
     return signature;
@@ -650,6 +653,8 @@ class PipeSymbol implements Symbol {
 
   indexed(argument: Symbol): Symbol|undefined { return undefined; }
 
+  typeArguments(): Symbol[]|undefined { return this.type.typeArguments(); }
+
   private get tsType(): ts.Type {
     let type = this._tsType;
     if (!type) {
@@ -798,15 +803,6 @@ function getContainerOf(symbol: ts.Symbol, context: TypeContext): Symbol|undefin
   }
 }
 
-function getTypeParameterOf(type: ts.Type, name: string): ts.Type|undefined {
-  if (type && type.symbol && type.symbol.name == name) {
-    const typeArguments: ts.Type[] = (type as any).typeArguments;
-    if (typeArguments && typeArguments.length <= 1) {
-      return typeArguments[0];
-    }
-  }
-}
-
 function typeKindOf(type: ts.Type | undefined): BuiltinType {
   if (type) {
     if (type.flags & ts.TypeFlags.Any) {