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 gatsbyjs#3487; Fixes gatsbyjs#2925

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

@@ -0,0 +1,24 @@
+const createKey = require(`../create-key`)
+
+describe(`createKey`, () => {
+  it(`leaves valid strings as is`, () => {
+    ;[
+      [`01234`, `01234`],
+      [`description`, `description`],
+      [`_hello`, `_hello`],
+    ].forEach(([input, output]) => {
+      expect(createKey(input)).toBe(output)
+    })
+  })
+
+  it(`replaces invalid characters`, () => {
+    ;[
+      [`/hello`, `_hello`],
+      [`~/path/to/some/module`, `_path_to_some_module`],
+      [`/*`, `_`],
+      [`/*.js`, `_js`],
+    ].forEach(([input, output]) => {
+      expect(createKey(input)).toBe(output)
+    })
+  })
+})

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, `_`)
+
+  // TODO: figure out what to replace this with _OR_ change the expr
+  if (replaced.match(/^__/)) {
+    return replaced.replace(/^_{2,}/, `_`)
+  }
+
+  return replaced
 }

yarn.lock

@@ -549,7 +549,7 @@ axios@^0.17.1:
     follow-redirects "^1.2.5"
     is-buffer "^1.1.5"
 
-"axios@github:contentful/axios#fix/https-via-http-proxy":
+axios@contentful/axios#fix/https-via-http-proxy:
   version "0.17.1"
   resolved "https://codeload.github.com/contentful/axios/tar.gz/4b06f4a63db3ac16c99f7c61b584ef0e6d11f1af"
   dependencies: