feat(jsii): protect against prohibited member names (#506)

We are not currently rigged to handle some special methods
that have meaning in runtimes that we target (specifically,
'equals', 'hashCode' and 'GetHashCode'). Just prohibit them for now.

packages/jsii/lib/assembler.ts

@@ -922,6 +922,10 @@ export class Assembler implements Emitter {
       this._diagnostic(declaration, ts.DiagnosticCategory.Error, `Unable to compute signature for ${type.fqn}#${symbol.name}`);
       return;
     }
+    if (isProhibitedMemberName(symbol.name)) {
+      this._diagnostic(declaration, ts.DiagnosticCategory.Error, `Prohibited member name: ${symbol.name}`);
+      return;
+    }
     const parameters = await Promise.all(signature.getParameters().map(p => this._toParameter(p)));
 
     const returnType = signature.getReturnType();
@@ -987,6 +991,10 @@ export class Assembler implements Emitter {
     if (LOG.isTraceEnabled()) {
       LOG.trace(`Processing property: ${colors.green(type.fqn)}#${colors.cyan(symbol.name)}`);
     }
+    if (isProhibitedMemberName(symbol.name)) {
+      this._diagnostic(symbol.valueDeclaration, ts.DiagnosticCategory.Error, `Prohibited member name: ${symbol.name}`);
+      return;
+    }
 
     const signature = symbol.valueDeclaration as (ts.PropertySignature
       | ts.PropertyDeclaration
@@ -1604,4 +1612,19 @@ function noEmptyDict<T>(xs: {[key: string]: T}): {[key: string]: T} | undefined
  */
 function isErrorType(t: ts.Type) {
   return (t as any).intrinsicName === 'error';
+}
+
+/**
+ * These specifially cause trouble in C#, where we have to specificially annotate them as 'new' but our generator isn't doing that
+ *
+ * In C#, 'GetHashCode' is also problematic, but jsii already prevents you from naming a
+ * method that starts with 'get' so we don't need to do anything special for that.
+ */
+const PROHIBITED_MEMBER_NAMES = ['equals', 'hashcode'];
+
+/**
+ * Whether the given name is prohibited
+ */
+function isProhibitedMemberName(name: string) {
+  return PROHIBITED_MEMBER_NAMES.includes(name.toLowerCase());
 }

packages/jsii/test/negatives/neg.prohibited-member-name.ts

@@ -0,0 +1,8 @@
+// tslint:disable-next-line:comment-format
+///!MATCH_ERROR:Prohibited member name: equals
+
+export class SomeClass {
+  public equals(): boolean {
+    return true;
+  }
+}