Move editorconfig-to-prettier package into repo (#15394)

I'd like to vendor/upstream this code because it's been the topic of a handful of issues in its repo over the years, including https://github.com/josephfrazier/editorconfig-to-prettier/issues/9, https://github.com/josephfrazier/editorconfig-to-prettier/issues/21, and most recently https://github.com/josephfrazier/editorconfig-to-prettier/issues/24, and I feel that having it in-repo would be more appropriate (not to mention [the issues in _this_ repo that pertain to editorconfig parsing](https://github.com/search?q=repo%3Aprettier%2Fprettier+editorconfig++&type=issues&state=open)). I've elaborated on my thoughts in https://github.com/josephfrazier/editorconfig-to-prettier/issues/24#issuecomment-1718405985, which I'll quote below:

> hey @Drakmyth, thanks for continuing this conversation! I appreciate all the links you've provided that indicate existing intention and implementations of parsing non-standard/custom properties. It seems like this question might not be as simple as I thought it was previously.
> 
> @fisker, thanks for chiming in as well!
> 
> As you (@fisker) mentioned in [#16 (comment)](https://github.com/josephfrazier/editorconfig-to-prettier/pull/16#issuecomment-1486130040), this package was originally intended for use by Prettier, and while there are some other dependents (according to [github](https://github.com/josephfrazier/editorconfig-to-prettier/network/dependents?dependent_type=PACKAGE) and [npm](https://www.npmjs.com/package/editorconfig-to-prettier?activeTab=dependents)), Prettier is still the vast majority of the usage this package sees.
> 
> Given that, I think it might make sense for this package's code/functionality to move into the Prettier repository, so that any issues relating to it can be discussed where it's used. Personally, I don't use `.editorconfig` with Prettier, so I don't feel especially well-positioned to make decisions on how things should work, especially when [the output of this package is subsequently modified by Prettier](https://github.com/prettier/prettier/blob/7c512651f8814924a042034ff821190c68ef409d/src/config/resolve-editorconfig.js#L13-L16) (I think you had also [mentioned](https://github.com/prettier/prettier/issues/14514#issuecomment-1471056464) this previously, @fisker), indicating that its behavior is already divergent from the intended use case.
> 
> What do y'all think of that proposal? If we have https://github.com/prettier/prettier/ vendor this repository's code, then I can archive this repo and direct people to discuss functionality in the Prettier issues.

This also implements @fisker's suggested change to ES module syntax from https://github.com/josephfrazier/editorconfig-to-prettier/pull/16/, as it's required for lint/test etc to pass.

Once this is merged, I'll likely archive the https://github.com/josephfrazier/editorconfig-to-prettier/ repo after adding a note directing any visitors here instead.

---

* Vendor editorconfig-to-prettier.js from https://github.com/josephfrazier/editorconfig-to-prettier/blob/8bb8226c40d7f2c8cf629301576850876c8617d4/index.js

* WIP Use `require` instead of `import`

* Revert "WIP Use `require` instead of `import`"

This reverts commit 4656b727960822b3d9d0659b68c99d8fa9a9ba58.

* Use `export` in editorconfig-to-prettier.js instead of `module.exports`, see https://github.com/josephfrazier/editorconfig-to-prettier/pull/16/

Copied from https://raw.githubusercontent.com/josephfrazier/editorconfig-to-prettier/e245d7051f3e2a1153b82362ed241f3f7482ab18/index.js

* `yarn fix`

* Add tests/unit/editorconfig-to-prettier.js from https://github.com/josephfrazier/editorconfig-to-prettier/pull/16/

Copied from https://raw.githubusercontent.com/josephfrazier/editorconfig-to-prettier/9effd580e7b6722007e1ace9913512e450cda46f/test.js

* tests/unit/editorconfig-to-prettier.js: Fix path to implementation

* WIP Naively convert assert.deepEqual to expect/toStrictEqual, see https://github.com/prettier/prettier/pull/15394#issuecomment-1718623556

* Wrap `test()` around `expect` calls

* XXX Force a middle test to fail to ensure the syntax works

* Revert "XXX Force a middle test to fail to ensure the syntax works"

This reverts commit 947eb34e1175944ebebf0a6271e13af99adcd663.

* `yarn fix`

src/config/editorconfig-to-prettier.js

@@ -0,0 +1,75 @@
+function removeUnset(editorConfig) {
+  const result = {};
+  const keys = Object.keys(editorConfig);
+  for (let i = 0; i < keys.length; i++) {
+    const key = keys[i];
+    if (editorConfig[key] === "unset") {
+      continue;
+    }
+    result[key] = editorConfig[key];
+  }
+  return result;
+}
+
+function editorConfigToPrettier(editorConfig) {
+  if (!editorConfig) {
+    return null;
+  }
+
+  editorConfig = removeUnset(editorConfig);
+
+  if (Object.keys(editorConfig).length === 0) {
+    return null;
+  }
+
+  const result = {};
+
+  if (editorConfig.indent_style) {
+    result.useTabs = editorConfig.indent_style === "tab";
+  }
+
+  if (editorConfig.indent_size === "tab") {
+    result.useTabs = true;
+  }
+
+  if (result.useTabs && editorConfig.tab_width) {
+    result.tabWidth = editorConfig.tab_width;
+  } else if (
+    editorConfig.indent_style === "space" &&
+    editorConfig.indent_size &&
+    editorConfig.indent_size !== "tab"
+  ) {
+    result.tabWidth = editorConfig.indent_size;
+  } else if (editorConfig.tab_width !== undefined) {
+    result.tabWidth = editorConfig.tab_width;
+  }
+
+  if (editorConfig.max_line_length) {
+    if (editorConfig.max_line_length === "off") {
+      result.printWidth = Number.POSITIVE_INFINITY;
+    } else {
+      result.printWidth = editorConfig.max_line_length;
+    }
+  }
+
+  if (editorConfig.quote_type === "single") {
+    result.singleQuote = true;
+  } else if (editorConfig.quote_type === "double") {
+    result.singleQuote = false;
+  }
+
+  if (["cr", "crlf", "lf"].includes(editorConfig.end_of_line)) {
+    result.endOfLine = editorConfig.end_of_line;
+  }
+
+  if (
+    editorConfig.insert_final_newline === false ||
+    editorConfig.insert_final_newline === true
+  ) {
+    result.insertFinalNewline = editorConfig.insert_final_newline;
+  }
+
+  return result;
+}
+
+export default editorConfigToPrettier;

src/config/resolve-editorconfig.js

@@ -1,6 +1,6 @@
 import path from "node:path";
 import editorconfig from "editorconfig";
-import editorConfigToPrettier from "editorconfig-to-prettier";
+import editorConfigToPrettier from "./editorconfig-to-prettier.js";
 import findProjectRoot from "./find-project-root.js";
 
 async function loadEditorConfig(filePath) {