fix: prevent invalid graphql field names from being created (#3994)

* fix: prevent invalid graphql field names from being created

Note: This will currently transform (for example) `/*` into `_` so I'm not quite sure what the best course of action is to replace that

Fixes #3487; Fixes #2925

* chore: revert yarn lock change

* test: simplify tests

* fix: dasherize after leading underscore

packages/gatsby/src/schema/__tests__/create-key.js

@@ -0,0 +1,26 @@
+const createKey = require(`../create-key`)
+
+describe(`createKey`, () => {
+  it(`leaves valid strings as is`, () => {
+    ;[`01234`, `validstring`, `_hello`, `_`].forEach(input => {
+      expect(createKey(input)).toBe(input)
+    })
+  })
+
+  it(`replaces invalid characters`, () => {
+    ;[
+      [`/hello`, `_hello`],
+      [`~/path/to/some/module`, `_-path-to-some-module`],
+      [`/*`, `_-`],
+      [`/*.js`, `_--js`],
+    ].forEach(([input, output]) => {
+      expect(createKey(input)).toBe(output)
+    })
+  })
+
+  it(`does not generate same key for different input`, () => {
+    ;[[`/*.js`, `*js`]].forEach(([one, two]) => {
+      expect(createKey(one)).not.toBe(createKey(two))
+    })
+  })
+})

packages/gatsby/src/schema/create-key.js

@@ -1,6 +1,6 @@
 // @flow
 const invariant = require(`invariant`)
-const regex = new RegExp(`[^a-zA-Z0-9_]`, `g`)
+const nonAlphaNumericExpr = new RegExp(`[^a-zA-Z0-9_]`, `g`)
 
 /**
  * GraphQL field names must be a string and cannot contain anything other than
@@ -14,5 +14,12 @@ module.exports = (key: string): string => {
     `Graphql field name (key) is not a string -> ${key}`
   )
 
-  return key.replace(regex, `_`)
+  const replaced = key.replace(nonAlphaNumericExpr, `_`)
+
+  // key is invalid; normalize with a leading underscore and dasherize rest
+  if (replaced.match(/^__/)) {
+    return replaced.replace(/_/g, (char, index) => (index === 0 ? `_` : `-`))
+  }
+
+  return replaced
 }