Pagination: let data key be a function

So that pagination data key can be determined dynamically,
based on a callback function that gets passed all template
data. So you can do something like:

    ---js
    {
      pagination: {
        data: (data) => {
          return "collections." + data.foo;
        },
    ...

src/Plugins/Pagination.js

@@ -2,6 +2,7 @@ const lodashChunk = require("lodash/chunk");
 const lodashGet = require("lodash/get");
 const lodashSet = require("lodash/set");
 const EleventyBaseError = require("../EleventyBaseError");
+const getPaginationDataKey = require("../Util/GetPaginationDataKey");
 
 class PaginationConfigError extends EleventyBaseError {}
 class PaginationError extends EleventyBaseError {}
@@ -30,13 +31,13 @@ class Pagination {
     return Pagination.hasPagination(this.data);
   }
 
-  circularReferenceCheck(data) {
-    if (data.eleventyExcludeFromCollections) {
+  circularReferenceCheck() {
+    if (this.data.eleventyExcludeFromCollections) {
       return;
     }
 
-    let key = data.pagination.data;
-    let tags = data.tags || [];
+    let key = getPaginationDataKey(this.data);
+    let tags = this.data.tags || [];
     for (let tag of tags) {
       if (`collections.${tag}` === key) {
         throw new PaginationError(
@@ -63,7 +64,7 @@ class Pagination {
     } else if (!("size" in data.pagination)) {
       throw new Error("Missing pagination size in front matter data.");
     }
-    this.circularReferenceCheck(data);
+    this.circularReferenceCheck();
 
     this.size = data.pagination.size;
     this.alias = data.pagination.alias;
@@ -76,10 +77,6 @@ class Pagination {
     this.template = tmpl;
   }
 
-  _getDataKey() {
-    return this.data.pagination.data;
-  }
-
   doResolveToObjectValues() {
     if ("resolve" in this.data.pagination) {
       return this.data.pagination.resolve === "values";
@@ -102,7 +99,7 @@ class Pagination {
 
   _resolveItems() {
     let notFoundValue = "__NOT_FOUND_ERROR__";
-    let key = this._getDataKey();
+    let key = getPaginationDataKey(this.data);
     let fullDataSet = lodashGet(this.data, key, notFoundValue);
     if (fullDataSet === notFoundValue) {
       throw new Error(
@@ -195,7 +192,7 @@ class Pagination {
 
       let override = {
         pagination: {
-          data: this.data.pagination.data,
+          data: getPaginationDataKey(this.data),
           size: this.data.pagination.size,
           alias: this.alias,
 

src/TemplateMap.js

@@ -5,6 +5,7 @@ const EleventyErrorUtil = require("./EleventyErrorUtil");
 const UsingCircularTemplateContentReferenceError = require("./Errors/UsingCircularTemplateContentReferenceError");
 const debug = require("debug")("Eleventy:TemplateMap");
 const debugDev = require("debug")("Dev:Eleventy:TemplateMap");
+const getPaginationDataKey = require("./Util/GetPaginationDataKey");
 
 const EleventyBaseError = require("./EleventyBaseError");
 
@@ -71,16 +72,14 @@ class TemplateMap {
    */
   isPaginationOverAllCollections(entry) {
     if (entry.data.pagination && entry.data.pagination.data) {
-      return (
-        entry.data.pagination.data === "collections" ||
-        entry.data.pagination.data === "collections.all"
-      );
+      const key = getPaginationDataKey(entry.data);
+      return key === "collections" || key === "collections.all";
     }
   }
 
   getPaginationTagTarget(entry) {
     if (entry.data.pagination && entry.data.pagination.data) {
-      return this.getTagTarget(entry.data.pagination.data);
+      return this.getTagTarget(getPaginationDataKey(entry.data));
     }
   }
 

src/Util/GetPaginationDataKey.js

@@ -0,0 +1,7 @@
+const lodashIsFunction = require("lodash/isFunction");
+
+module.exports = function (data) {
+  return lodashIsFunction(data.pagination.data)
+    ? data.pagination.data(data)
+    : data.pagination.data;
+};

test/GetPaginationDataKeyTest.js

@@ -0,0 +1,13 @@
+const test = require("ava");
+const getPaginationDataKey = require("../src/Util/GetPaginationDataKey");
+
+test("getPaginationDataKey when key is string", (t) => {
+  t.is(getPaginationDataKey({pagination: {data: "foo"}}), "foo");
+});
+
+test("getPaginationDataKey when key is function", (t) => {
+  t.is(
+    getPaginationDataKey({foo: "bar", pagination: {data: (data) => data.foo}}),
+    "bar"
+  );
+});