Allow testing certain code blocks on only specific TypeScript versions

Author: benjie

integrationTests/ts/.gitignore

@@ -0,0 +1,2 @@
+# TypeScript files are generated from templates; see test.js
+*.ts

integrationTests/ts/index.ts renamed to integrationTests/ts/index.ts.template

@@ -13,8 +13,7 @@ const example: SomeExtension = {
 };
 
 // The following code block requires a newer version of TypeScript
-/*! >=3.2
-
+/*! >=3.2 !*/
 declare module 'graphql' {
   interface GraphQLObjectTypeExtensions<TSource = any, TContext = any> {
     someObjectExtension?: SomeExtension;
@@ -30,7 +29,7 @@ declare module 'graphql' {
     someArgumentExtension?: SomeExtension;
   }
 }
-*/
+/*!!*/
 
 const queryType: GraphQLObjectType = new GraphQLObjectType({
   name: 'Query',

integrationTests/ts/package.json

@@ -3,7 +3,9 @@
     "test": "node test.js"
   },
   "dependencies": {
+    "glob": "^7.1.6",
     "graphql": "file:../../npmDist",
+    "semver": "^7.3.2",
     "typescript-2.6": "npm:[email protected]",
     "typescript-2.7": "npm:[email protected]",
     "typescript-2.8": "npm:[email protected]",

integrationTests/ts/test.js

@@ -4,16 +4,56 @@
 
 const path = require('path');
 const childProcess = require('child_process');
+const assert = require('assert');
+const fs = require('fs');
+
+const glob = require('glob');
+const semver = require('semver');
 
 const { dependencies } = require('./package.json');
 
 const tsVersions = Object.keys(dependencies)
   .filter((pkg) => pkg.startsWith('typescript-'))
   .sort((a, b) => b.localeCompare(a));
 
+// To allow omitting certain code from older versions of TypeScript, we have a
+// "magic" comment syntax. We precede a block of code with:
+//
+//     /*! SEMVER_RANGE !*/
+//
+// replacing SEMVER_RANGE with a semver range spec, such as '>=3.2'; we
+// terminate the block of code with:
+//
+//     /*!!*/
+//
+// We will only include the code between these comments if the TypeScript
+// version being tested satisfies the semver range that was specified. NOTE: We
+// currently do not allow nesting of these blocks.
+const templates = glob.sync('./*.ts.template').map((filename) => {
+  const content = fs.readFileSync(filename, 'utf8');
+  const targetFilename = filename.replace(/\.template$/, '');
+  assert.notEqual(filename, targetFilename);
+  const writeFileSync = (version) => {
+    // Captures our magic comment syntax: `/*!(CAPTURE1)!*/(CAPTURE 2)/*!!*/`
+    const regex = /\/\*!([^!]+)!\*\/([\s\S]*?)\/\*!!\*\//g;
+    const finalContent = content.replace(regex, (_, versionRange, payload) => {
+      if (semver.satisfies(version, versionRange)) {
+        return payload;
+      }
+      return '';
+    });
+    fs.writeFileSync(targetFilename, finalContent);
+  };
+  return { writeFileSync };
+});
+
 for (const version of tsVersions) {
   console.log(`Testing on ${version} ...`);
 
+  for (const template of templates) {
+    template.writeFileSync(version);
+  }
+
   const tscPath = path.join(__dirname, 'node_modules', version, 'bin/tsc');
   childProcess.execSync(tscPath, { stdio: 'inherit' });
 }