Process source maps in Rust instead of JS (#1280)

- Improves speed and binary size significantly.
- Makes deno_last_exception() output a JSON structure.
- Isolate::execute and Isolate::event_loop now return
  structured, mapped JSError objects on errors.
- Removes libdeno functions:
  libdeno.setGlobalErrorHandler()
  libdeno.setPromiseRejectHandler()
  libdeno.setPromiseErrorExaminer()

In collaboration with Ryan Dahl.

js/compiler.ts

@@ -3,10 +3,8 @@ import * as ts from "typescript";
 import { MediaType } from "gen/msg_generated";
 
 import { assetSourceCode } from "./assets";
-import { libdeno } from "./libdeno";
 import * as os from "./os";
 import { CodeProvider } from "./runner";
-import { RawSourceMap } from "./types";
 import { assert, log, notImplemented } from "./util";
 
 const EOL = "\n";
@@ -71,7 +69,7 @@ export class ModuleMetaData implements ts.IScriptSnapshot {
     public readonly mediaType: MediaType,
     public readonly sourceCode: SourceCode = "",
     public outputCode: OutputCode = "",
-    public sourceMap: SourceMap | RawSourceMap = ""
+    public sourceMap: SourceMap = ""
   ) {
     if (outputCode !== "" || fileName.endsWith(".d.ts")) {
       this.scriptVersion = "1";
@@ -131,8 +129,6 @@ export class Compiler
     ContainingFile,
     Map<ModuleSpecifier, ModuleFileName>
   >();
-  // Keep track of state of the last module requested via `getGeneratedContents`
-  private _lastModule: ModuleMetaData | undefined;
   // A reference to the log utility, so it can be monkey patched during testing
   private _log = log;
   // A map of module file names to module meta data
@@ -369,19 +365,15 @@ export class Compiler
       moduleMetaData.outputCode = `${
         outputFile.text
       }\n//# sourceURL=${fileName}`;
-      moduleMetaData.sourceMap = JSON.parse(sourceMapFile.text);
+      moduleMetaData.sourceMap = sourceMapFile.text;
     }
 
     moduleMetaData.scriptVersion = "1";
-    const sourceMap =
-      moduleMetaData.sourceMap === "string"
-        ? moduleMetaData.sourceMap
-        : JSON.stringify(moduleMetaData.sourceMap);
     this._os.codeCache(
       fileName,
       sourceCode,
       moduleMetaData.outputCode,
-      sourceMap
+      moduleMetaData.sourceMap
     );
     return moduleMetaData.outputCode;
   }
@@ -398,36 +390,10 @@ export class Compiler
   }
 
   /** Given a fileName, return what was generated by the compiler. */
-  getGeneratedContents = (fileName: string): string | RawSourceMap => {
-    this._log("compiler.getGeneratedContents", fileName);
-    if (fileName === "gen/bundle/main.js") {
-      assert(libdeno.mainSource.length > 0);
-      return libdeno.mainSource;
-    } else if (fileName === "main.js.map") {
-      return libdeno.mainSourceMap;
-    } else if (fileName === "deno_main.js") {
-      return "";
-    } else if (!fileName.endsWith(".map")) {
-      const moduleMetaData = this._moduleMetaDataMap.get(fileName);
-      if (!moduleMetaData) {
-        this._lastModule = undefined;
-        return "";
-      }
-      this._lastModule = moduleMetaData;
-      return moduleMetaData.outputCode;
-    } else {
-      if (this._lastModule && this._lastModule.sourceMap) {
-        // Assuming the the map will always be asked for after the source
-        // code.
-        const { sourceMap } = this._lastModule;
-        this._lastModule = undefined;
-        return sourceMap;
-      } else {
-        // Errors thrown here are caught by source-map.
-        throw new Error(`Unable to find source map: "${fileName}"`);
-      }
-    }
-  };
+  getGeneratedSourceMap(fileName: string): string {
+    const moduleMetaData = this._moduleMetaDataMap.get(fileName);
+    return moduleMetaData ? moduleMetaData.sourceMap : "";
+  }
 
   /** Get the output code for a module based on its filename. A call to
    * `.getFilename()` should occur before attempting to get the output code as