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;
@@ -129,16 +130,18 @@ class Pagination {
 
   _has(target, key) {
     let notFoundValue = "__NOT_FOUND_ERROR__";
-    let data = lodashGet(target, key, notFoundValue);
+    let paginationDataKey = getPaginationDataKey(this.data);
+    let data = lodashGet(target, paginationDataKey, notFoundValue);
     return data !== notFoundValue;
   }
 
   _get(target, key) {
     let notFoundValue = "__NOT_FOUND_ERROR__";
-    let data = lodashGet(target, key, notFoundValue);
+    let paginationDataKey = getPaginationDataKey(this.data);
+    let data = lodashGet(target, paginationDataKey, notFoundValue);
     if (data === notFoundValue) {
       throw new Error(
-        `Could not find pagination data, went looking for: ${key}`
+        `Could not find pagination data, went looking for: ${paginationDataKey}`
       );
     }
     return data;
@@ -205,7 +208,7 @@ class Pagination {
   getOverrideData(pageItems) {
     let override = {
       pagination: {
-        data: this.data.pagination.data,
+        data: getPaginationDataKey(this.data),
         size: this.data.pagination.size,
         alias: this.alias,
         items: pageItems,

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");
 
@@ -78,16 +79,14 @@ 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"
+  );
+});

test/PaginationTest.js

@@ -654,6 +654,20 @@ test("Pagination `before` Callback with a Filter", async (t) => {
   t.deepEqual(templates[0].data.myalias, "item2");
 });
 
+test("Pagination when `data` is a function", async (t) => {
+  let tmpl = getNewTemplate(
+    "./test/stubs/paged/paged-data-key-func.njk",
+    "./test/stubs/",
+    "./dist"
+  );
+
+  let data = await tmpl.getData();
+  let templates = await tmpl.getTemplates(data);
+  t.is(templates.length, 2);
+  t.deepEqual(templates[0].data.pagination.items, ["foo"]);
+  t.deepEqual(templates[1].data.pagination.items, ["woo"]);
+});
+
 test("Pagination `before` Callback with `reverse: true` (test order of operations)", async (t) => {
   let tmpl = getNewTemplate(
     "./test/stubs/paged/paged-before-and-reverse.njk",

test/stubs/paged/paged-data-key-func.njk

@@ -0,0 +1,11 @@
+---js
+{
+  dataCanBeFoundIn: "items",
+  pagination: {
+    data: (data) => data.dataCanBeFoundIn,
+    size: 1
+  },
+  items: ["foo", "woo"]
+}
+---
+<ol>{% for item in pagination.items %}<li>{{ item }}</li>{% endfor %}</ol>