Allow nested consumer usage

dist/source-map.js

@@ -2919,7 +2919,7 @@ module.exports = function wasm() {
     return cachedWasm;
   }
 
-  let currentCallback = null;
+  const callbackStack = [];
 
   cachedWasm = readWasm().then(buffer => {
       return WebAssembly.instantiate(buffer, {
@@ -2960,7 +2960,7 @@ module.exports = function wasm() {
               }
             }
 
-            currentCallback(mapping);
+            callbackStack[callbackStack.length - 1](mapping);
           },
 
           start_all_generated_locations_for: function () { console.time("all_generated_locations_for"); },
@@ -2989,11 +2989,11 @@ module.exports = function wasm() {
     return {
       exports: wasm.instance.exports,
       withMappingCallback: (mappingCallback, f) => {
-        currentCallback = mappingCallback;
+        callbackStack.push(mappingCallback)
         try {
           f();
         } finally {
-          currentCallback = null;
+          callbackStack.pop()
         }
       }
     };

lib/wasm.js

@@ -20,7 +20,7 @@ module.exports = function wasm() {
     return cachedWasm;
   }
 
-  let currentCallback = null;
+  const callbackStack = [];
 
   cachedWasm = readWasm().then(buffer => {
       return WebAssembly.instantiate(buffer, {
@@ -61,7 +61,7 @@ module.exports = function wasm() {
               }
             }
 
-            currentCallback(mapping);
+            callbackStack[callbackStack.length - 1](mapping);
           },
 
           start_all_generated_locations_for: function () { console.time("all_generated_locations_for"); },
@@ -90,11 +90,11 @@ module.exports = function wasm() {
     return {
       exports: wasm.instance.exports,
       withMappingCallback: (mappingCallback, f) => {
-        currentCallback = mappingCallback;
+        callbackStack.push(mappingCallback)
         try {
           f();
         } finally {
-          currentCallback = null;
+          callbackStack.pop()
         }
       }
     };

test/test-nested-consumer-usage.js

@@ -0,0 +1,80 @@
+const {SourceMapConsumer, SourceMapGenerator} = require('../')
+
+const tsMap = {
+  version: 3,
+  file: "blah.js",
+  sourceRoot: "",
+  sources: ["blah.tsx"],
+  names: [],
+  mappings:
+    ";;AAKA;IACE,MAAM,CAAC,EAAC,MAAM,EAAE,SAAS,EAAC,CAAC;AAC7B,CAAC;AAFD,yBAEC",
+  sourcesContent: [
+    "\ntype Cheese = {\n  readonly cheese: string\n}\n\nexport default function Cheese(): Cheese {\n  return {cheese: 'stilton'};\n}\n"
+  ]
+};
+
+const babelMap = {
+  version: 3,
+  sources: ["blah.tsx"],
+  names: [
+    "Object",
+    "defineProperty",
+    "exports",
+    "value",
+    "Cheese",
+    "cheese",
+    "default"
+  ],
+  mappings:
+    "AAAA;;AACAA,OAAOC,cAAP,CAAsBC,OAAtB,EAA+B,YAA/B,EAA6C,EAAEC,OAAO,IAAT,EAA7C;AACA,SAASC,MAAT,GAAkB;AACd,WAAO,EAAEC,QAAQ,SAAV,EAAP;AACH;AACDH,QAAQI,OAAR,GAAkBF,MAAlB",
+  sourcesContent: [
+    '"use strict";\nObject.defineProperty(exports, "__esModule", { value: true });\nfunction Cheese() {\n    return { cheese: \'stilton\' };\n}\nexports.default = Cheese;\n//# sourceMappingURL=blah.js.map'
+  ]
+};
+
+
+async function composeSourceMaps(
+  tsMap,
+  babelMap,
+  tsFileName,
+) {
+  const tsConsumer = await new SourceMapConsumer(tsMap)
+  const babelConsumer = await new SourceMapConsumer(babelMap)
+  const map = new SourceMapGenerator()
+  babelConsumer.eachMapping(
+    ({
+      source,
+      generatedLine,
+      generatedColumn,
+      originalLine,
+      originalColumn,
+      name,
+    }) => {
+      if (originalLine) {
+        const original = tsConsumer.originalPositionFor({
+          line: originalLine,
+          column: originalColumn,
+        })
+        if (original.line) {
+          map.addMapping({
+            generated: {
+              line: generatedLine,
+              column: generatedColumn,
+            },
+            original: {
+              line: original.line,
+              column: original.column,
+            },
+            source: tsFileName,
+            name: name,
+          })
+        }
+      }
+    }
+  )
+  return map.toJSON()
+}
+
+exports["test nested consumer usage"] = async function (assert) {
+  await composeSourceMaps(tsMap, babelMap, 'blah.tsx')
+};