fix(assembler): handle unknown types without crashing (#501)

After failing compilation we proceed with jsii analysis, to give as much
information as possible in one go.

However, some compilation failures lead to a lack of information that
make the jsii analyzer crash, which ultimately leads jsii to fail with
no more information than:

    Error: TypeError: Cannot read property 'getJsDocTags' of undefined

Fix this in two ways:

- First, detect the situation where this occurs and produce a more
  useful error message.
- Guard against this happening in general by catching exceptions
  during type analysis and still printing the compilation errors.

packages/jsii/lib/assembler.ts

@@ -377,7 +377,6 @@ export class Assembler implements Emitter {
 
     const processBaseTypes = (types: ts.Type[]) => {
       for (const iface of types) {
-
         // base is private/internal, so we continue recursively with it's own bases
         if (this._isPrivateOrInternal(iface.symbol)) {
           erasedBases.push(iface);
@@ -507,7 +506,7 @@ export class Assembler implements Emitter {
     // process all "implements" clauses
     const allInterfaces = new Set<string>();
     for (const clause of implementsClauses) {
-      const { interfaces } = await this._processBaseInterfaces(fqn, clause.types.map(t => this._typeChecker.getTypeFromTypeNode(t)));
+      const { interfaces } = await this._processBaseInterfaces(fqn, clause.types.map(t => this._getTypeFromTypeNode(t)));
       for (const ifc of (interfaces || [])) {
         allInterfaces.add(ifc.fqn);
       }
@@ -623,6 +622,17 @@ export class Assembler implements Emitter {
     return _sortMembers(jsiiType);
   }
 
+  /**
+   * Use the TypeChecker's getTypeFromTypeNode, but throw a descriptive error if it fails
+   */
+  private _getTypeFromTypeNode(t: ts.TypeNode) {
+    const type = this._typeChecker.getTypeFromTypeNode(t);
+    if (isErrorType(type)) {
+      throw new Error(`Unable to resolve type: ${t.getFullText()}. This typically happens if something is wrong with your dependency closure.`);
+    }
+    return type;
+  }
+
   /**
    * Check that this class doesn't declare any members that are of different staticness in itself or any of its bases
    */
@@ -1585,3 +1595,13 @@ function noEmptyDict<T>(xs: {[key: string]: T}): {[key: string]: T} | undefined
   if (Object.keys(xs).length === 0) { return undefined; }
   return xs;
 }
+
+/**
+ * Check whether this type is the intrinsic TypeScript "error type"
+ *
+ * This type is returned if type lookup fails. Unfortunately no public
+ * accessors for it are exposed.
+ */
+function isErrorType(t: ts.Type) {
+  return (t as any).intrinsicName === 'error';
+}

packages/jsii/lib/compiler.ts

@@ -141,22 +141,30 @@ export class Compiler implements Emitter {
 
     private async _consumeProgram(program: ts.Program, stdlib: string): Promise<EmitResult> {
         const emit = program.emit();
-        if (emit.emitSkipped) {
+        let hasErrors = emitHasErrors(emit);
+        const diagnostics = [...emit.diagnostics];
+
+        if (hasErrors) {
             LOG.error('Compilation errors prevented the JSII assembly from being created');
         }
 
         // we continue to do jsii checker even if there are compilation errors so that
-        // jsii warnings will appear.
-        const assembler = new Assembler(this.options.projectInfo, program, stdlib);
-        const assmEmit = await assembler.emit();
-        if (assmEmit.hasErrors) {
-            LOG.error('Type model errors prevented the JSII assembly from being created');
+        // jsii warnings will appear. However, the Assembler might throw an exception
+        // because broken/missing type information might lead it to fail completely.
+        try {
+            const assembler = new Assembler(this.options.projectInfo, program, stdlib);
+            const assmEmit = await assembler.emit();
+            if (assmEmit.hasErrors) {
+                LOG.error('Type model errors prevented the JSII assembly from being created');
+            }
+
+            hasErrors = hasErrors || assmEmit.hasErrors;
+            diagnostics.push(...assmEmit.diagnostics);
+        } catch (e) {
+            LOG.error(`Error during type model analysis: ${e}`);
         }
 
-        return {
-            hasErrors: emit.emitSkipped || assmEmit.hasErrors,
-            diagnostics: [...emit.diagnostics, ...assmEmit.diagnostics]
-        };
+        return { hasErrors, diagnostics };
     }
 
     /**
@@ -353,3 +361,7 @@ function parseConfigHostFromCompilerHost(host: ts.CompilerHost): ts.ParseConfigH
         trace: host.trace ? (s) => host.trace!(s) : undefined
     };
 }
+
+function emitHasErrors(result: ts.EmitResult) {
+    return result.diagnostics.some(d => d.category === ts.DiagnosticCategory.Error) || result.emitSkipped;
+}