Generate @apollo/client/invariantErrorCodes.js for each release.

When an invariant fails in production, a cryptic numeric error of the form
`Invariant Violation: 42` is thrown, with a reference to the error codes
section of invariant-packages README.md: https://github.com/apollographql/invariant-packages#error-codes

This vague guidance has not proven adequate in many cases, to say the
least: see apollographql/invariant-packages#18,
apollographql/invariant-packages#19, #6604,

Using error codes instead of error strings remains important for
production bundle sizes, but I think we can make it substantially easier
to look up the error string corresponding to each error code, by
generating a single file containing all the invariant error codes for each
@apollo/client release.

Starting with Apollo Client 3.1.0, this manifest file can be found in
@apollo/client/invariantErrorCodes.js (using an npm/yarn-installed copy of
@apollo/client, since this file is generated in the ./dist directory, not
checked into the repository). The file contains an explanatory comment,
the @apollo/client version, and a sequential map from error numbers to the
{ file, node } responsible for the error.

I wish we could go back and republish old versions of @apollo/client to
include this file, but at least things should be easier going forward.

config/processInvariants.ts

@@ -1,36 +1,78 @@
-import { readFileSync, writeFileSync } from "fs";
-import { resolve, relative } from "path";
+import * as fs from "fs";
+import * as path from "path";
 import glob = require("glob");
 
-const distDir = resolve(__dirname, "..", "dist");
+const distDir = path.resolve(__dirname, "..", "dist");
 
 glob(`${distDir}/**/*.js`, (error, files) => {
   if (error) throw error;
 
   files.sort().forEach(file => {
-    const relPath = relative(distDir, file);
+    const relPath = path.relative(distDir, file);
 
     // Outside the distDir, somehow.
     if (relPath.startsWith("../")) return;
 
     // Avoid re-transforming CommonJS bundle files.
     if (relPath.endsWith(".cjs.js")) return;
 
-    const source = readFileSync(file, "utf8");
+    const source = fs.readFileSync(file, "utf8");
     const output = transform(source, relPath);
     if (source !== output) {
       console.log("transformed invariants in " + relPath);
-      writeFileSync(file, output, "utf8");
+      fs.writeFileSync(file, output, "utf8");
     }
   });
+
+  fs.writeFileSync(
+    path.join(distDir, "invariantErrorCodes.js"),
+    recast.print(errorCodeManifest, {
+      tabWidth: 2,
+    }).code + "\n",
+  );
 });
 
 import * as recast from "recast";
 import * as parser from "recast/parsers/babel";
 const b = recast.types.builders;
+const n = recast.types.namedTypes;
+type Node = recast.types.namedTypes.Node;
+type NumericLiteral = recast.types.namedTypes.NumericLiteral;
+type CallExpression = recast.types.namedTypes.CallExpression;
+type NewExpression = recast.types.namedTypes.NewExpression;
 let nextErrorCode = 1;
 
-function transform(code: string, id: string) {
+const errorCodeManifest = b.objectExpression([
+  b.property("init",
+    b.stringLiteral("@apollo/client version"),
+    b.stringLiteral(require("../package.json").version),
+  ),
+]);
+
+errorCodeManifest.comments = [
+  b.commentLine(' This file is meant to help with looking up the source of errors like', true),
+  b.commentLine(' "Invariant Violation: 35" and is automatically generated by the file', true),
+  b.commentLine(' @apollo/client/config/processInvariants.ts for each @apollo/client', true),
+  b.commentLine(' release. The numbers may change from release to release, so please', true),
+  b.commentLine(' consult the @apollo/client/invariantErrorCodes.js file specific to', true),
+  b.commentLine(' your @apollo/client version. This file is not meant to be imported.', true),
+];
+
+function getErrorCode(
+  file: string,
+  expr: CallExpression | NewExpression,
+): NumericLiteral {
+  const numLit = b.numericLiteral(nextErrorCode++);
+  errorCodeManifest.properties.push(
+    b.property("init", numLit, b.objectExpression([
+      b.property("init", b.identifier("file"), b.stringLiteral(file)),
+      b.property("init", b.identifier("node"), expr),
+    ])),
+  );
+  return numLit;
+}
+
+function transform(code: string, file: string) {
   // If the code doesn't seem to contain anything invariant-related, we
   // can skip parsing and transforming it.
   if (!/invariant/i.test(code)) {
@@ -50,7 +92,7 @@ function transform(code: string, id: string) {
         }
 
         const newArgs = node.arguments.slice(0, 1);
-        newArgs.push(b.numericLiteral(nextErrorCode++));
+        newArgs.push(getErrorCode(file, node));
 
         return b.conditionalExpression(
           makeNodeEnvTest(),
@@ -80,9 +122,7 @@ function transform(code: string, id: string) {
           return;
         }
 
-        const newArgs = [
-          b.numericLiteral(nextErrorCode++),
-        ];
+        const newArgs = [getErrorCode(file, node)];
 
         return b.conditionalExpression(
           makeNodeEnvTest(),
@@ -99,11 +139,6 @@ function transform(code: string, id: string) {
   return recast.print(ast).code;
 }
 
-const n = recast.types.namedTypes;
-type Node = recast.types.namedTypes.Node;
-type CallExpression = recast.types.namedTypes.CallExpression;
-type NewExpression = recast.types.namedTypes.NewExpression;
-
 function isIdWithName(node: Node, ...names: string[]) {
   return n.Identifier.check(node) &&
     names.some(name => name === node.name);