fix(gatsby-cli): normalize case of windows drive letter (#20437)

This PR ensures that the current working directory on Windows always has an uppercase drive letter (i.e., C: vs. c:).

packages/gatsby-cli/src/index.ts

@@ -1,19 +1,26 @@
 #!/usr/bin/env node
 
 import "@babel/polyfill"
+import os from "os"
 import semver from "semver"
 import util from "util"
 import createCli from "./create-cli"
 import report from "./reporter"
 import pkg from "../package.json"
 import updateNotifier from "update-notifier"
+import ensureWindowsDriveLetterIsUppercase from "./util/ensure-windows-drive-letter-is-uppercase"
 
 const useJsonLogger = process.argv.slice(2).some(arg => arg.includes(`json`))
 
 if (useJsonLogger) {
   process.env.GATSBY_LOGGER = `json`
 }
 
+// Ensure stable runs on Windows when started from different shells (i.e. c:\dir vs C:\dir)
+if (os.platform() === `win32`) {
+  ensureWindowsDriveLetterIsUppercase()
+}
+
 // Check if update is available
 updateNotifier({ pkg }).notify({ isGlobal: true })
 

packages/gatsby-cli/src/util/ensure-windows-drive-letter-is-uppercase.js

@@ -0,0 +1,59 @@
+const { tmpdir } = require(`os`)
+const report = require(`../reporter`)
+
+/**
+ * This function ensures that the current working directory on Windows
+ * always has an uppercase drive letter (i.e., C: vs. c:).
+ *
+ * Why?
+ * 1. Different utils like "true-case-path", "normalize-path", "slash" treat Windows
+ * drive letter differently. "true-case-path" will uppercase, others usually don't care.
+ * As a result path normalization produces different results depending on current cwd (c: vs. C:)
+ * which manifests in weird bugs that are very hard to debug.
+ *
+ * We can't control community plugins or site code, so everything should be working
+ * even with a different set of libraries.
+ *
+ * Related: https://github.com/Profiscience/true-case-path/issues/3
+ *
+ * 2. Builds save some paths in a cache. If you run the first build from "c:" shell
+ * and then the next one from "C:" shell, you may get a bunch of webpack warnings
+ * because it expects module paths to be case-sensitive.
+ */
+module.exports = function ensureWindowsDriveLetterIsUppercase() {
+  const cwd = process.cwd()
+  const normalizedCwd = driveLetterToUpperCase(cwd)
+
+  if (cwd !== normalizedCwd) {
+    try {
+      // When cwd is "c:\dir" then command "cd C:\dir" won't do anything
+      // You have to change the dir twice to actually change the casing of the path
+      process.chdir(tmpdir())
+      process.chdir(normalizedCwd)
+    } catch {
+      // rollback
+      process.chdir(cwd)
+    }
+
+    if (normalizedCwd !== process.cwd()) {
+      report.warn(
+        report.stripIndent(`
+          Your working directory has a lower case drive letter:
+            "${cwd}".
+          ---^
+          For solid development experience, we recommend switching it to upper case:
+            cd "C:\\"
+            cd "${normalizedCwd}"
+          (Windows requires two directory switches to change the case of the drive letter)
+        `)
+      )
+    }
+  }
+}
+
+function driveLetterToUpperCase(path) {
+  const segments = path.split(`:\\`)
+  return segments.length > 1
+    ? segments.shift().toUpperCase() + `:\\` + segments.join(`:\\`)
+    : path
+}