Infer function expressions in matching contexts (#514)

* legalizes omitting types on function expressions within function type contexts
* legalizes omitting any number of arguments

Author: dcodeIO

src/ast.ts

@@ -864,6 +864,7 @@ export abstract class Node {
     body: Statement | null,
     decorators: DecoratorNode[] | null,
     flags: CommonFlags,
+    arrowKind: ArrowKind,
     range: Range
   ): FunctionDeclaration {
     var stmt = new FunctionDeclaration();
@@ -874,6 +875,7 @@ export abstract class Node {
     stmt.signature = signature;
     stmt.body = body;
     stmt.decorators = decorators;
+    stmt.arrowKind = arrowKind;
     return stmt;
   }
 
@@ -1773,6 +1775,16 @@ export class ForStatement extends Statement {
   statement: Statement;
 }
 
+/** Indicates the kind of an array function. */
+export const enum ArrowKind {
+  /** Not an arrow function. */
+  NONE,
+  /** Parenthesized parameter list. */
+  ARROW_PARENTHESIZED,
+  /** Single parameter without parenthesis. */
+  ARROW_SINGLE
+}
+
 /** Represents a `function` declaration. */
 export class FunctionDeclaration extends DeclarationStatement {
   kind = NodeKind.FUNCTIONDECLARATION;
@@ -1783,6 +1795,8 @@ export class FunctionDeclaration extends DeclarationStatement {
   signature: SignatureNode;
   /** Body statement. Usually a block. */
   body: Statement | null;
+  /** Arrow function kind, if applicable. */
+  arrowKind: ArrowKind;
 
   get isGeneric(): bool {
     var typeParameters = this.typeParameters;
@@ -1792,7 +1806,14 @@ export class FunctionDeclaration extends DeclarationStatement {
   /** Clones this function declaration. */
   clone(): FunctionDeclaration {
     return Node.createFunctionDeclaration(
-      this.name, this.typeParameters, this.signature, this.body, this.decorators, this.flags, this.range
+      this.name,
+      this.typeParameters,
+      this.signature,
+      this.body,
+      this.decorators,
+      this.flags,
+      this.arrowKind,
+      this.range
     );
   }
 }
@@ -1960,3 +1981,12 @@ export function mangleInternalPath(path: string): string {
   if (path.endsWith(".ts")) path = path.substring(0, path.length - 3);
   return path;
 }
+
+/** Tests if the specified type node represents an omitted type. */
+export function isTypeOmitted(type: CommonTypeNode): bool {
+  if (type.kind == NodeKind.TYPE) {
+    let name = (<TypeNode>type).name;
+    return !(name.next || name.identifier.text.length);
+  }
+  return false;
+}

src/common.ts

@@ -51,33 +51,31 @@ export enum CommonFlags {
   INSTANCE = 1 << 17,
   /** Is a constructor. */
   CONSTRUCTOR = 1 << 18,
-  /** Is an arrow function. */
-  ARROW = 1 << 19,
   /** Is a module export. */
-  MODULE_EXPORT = 1 << 20,
+  MODULE_EXPORT = 1 << 19,
   /** Is a module import. */
-  MODULE_IMPORT = 1 << 21,
+  MODULE_IMPORT = 1 << 20,
 
   // Compilation states
 
   /** Is resolved. */
-  RESOLVED = 1 << 22,
+  RESOLVED = 1 << 21,
   /** Is compiled. */
-  COMPILED = 1 << 23,
+  COMPILED = 1 << 22,
   /** Has a constant value and is therefore inlined. */
-  INLINED = 1 << 24,
+  INLINED = 1 << 23,
   /** Is scoped. */
-  SCOPED = 1 << 25,
+  SCOPED = 1 << 24,
   /** Is a trampoline. */
-  TRAMPOLINE = 1 << 26,
+  TRAMPOLINE = 1 << 25,
   /** Is a virtual method. */
-  VIRTUAL = 1 << 27,
+  VIRTUAL = 1 << 26,
   /** Is the main function. */
-  MAIN = 1 << 28,
+  MAIN = 1 << 27,
 
   // Other
 
-  QUOTED = 1 << 29
+  QUOTED = 1 << 28
 }
 
 /** Path delimiter inserted between file system levels. */