add docs-test

docs/features/scales.md

@@ -1013,7 +1013,7 @@ If the input channel is *data*, then the reducer is passed groups of the mark’
 
 Note: when the value of the sort option is a string or a function, it is interpreted as a mark [sort transform](../transforms/sort.md). To use both sort options and a mark sort transform, use [Plot.sort](../transforms/sort.md#sort-order-options).
 
-## scale(*options*)
+## scale(*options*) {#scale-options-1}
 
 You can also create a standalone scale with Plot.**scale**(*options*). The *options* object must define at least one scale; see [Scale options](#scale-options) for how to define a scale. For example, here is a linear color scale with the default domain of [0, 1] and default scheme *turbo*:
 

docs/interactions/pointer.md

@@ -180,7 +180,7 @@ To resolve the horizontal target position, the pointer transform applies the fol
 
 The same precedence applies to the **py**, **y**, **y1**, and **y2** channels.
 
-## pointer(*options*)
+## pointer(*options*) {#pointer-options-1}
 
 ```js
 Plot.tip(penguins, Plot.pointer({x: "culmen_length_mm", y: "culmen_depth_mm"}))

docs/marks/bar.md

@@ -232,7 +232,7 @@ The following optional channels are supported:
 
 If neither the **x1** nor **x2** option is specified, the **x** option may be specified as shorthand to apply an implicit [stackX transform](../transforms/stack.md); this is the typical configuration for a horizontal bar chart with bars aligned at *x* = 0. If the **x** option is not specified, it defaults to [identity](../features/transforms.md#identity). If *options* is undefined, then it defaults to **x2** as identity and **y** as the zero-based index [0, 1, 2, …]; this allows an array of numbers to be passed to barX to make a quick sequential bar chart. If the **y** channel is not specified, the bar will span the full vertical extent of the plot (or facet).
 
-If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each *x* to produce *x1*, and *interval*.offset(*x1*) is invoked for each *x1* to produce *x2*. If the interval is specified as a number *n*, *x1* and *x2* are taken as the two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each *x* to produce *x1*, and *interval*.offset(*x1*) is invoked for each *x1* to produce *x2*. If the interval is specified as a number *n*, *x1* and *x2* are taken as the two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 ## barY(*data*, *options*)
 
@@ -251,4 +251,4 @@ The following optional channels are supported:
 
 If neither the **y1** nor **y2** option is specified, the **y** option may be specified as shorthand to apply an implicit [stackY transform](../transforms/stack.md); this is the typical configuration for a vertical bar chart with bars aligned at *y* = 0. If the **y** option is not specified, it defaults to [identity](../features/transforms.md#identity). If *options* is undefined, then it defaults to **y2** as identity and **x** as the zero-based index [0, 1, 2, …]; this allows an array of numbers to be passed to barY to make a quick sequential bar chart. If the **x** channel is not specified, the bar will span the full horizontal extent of the plot (or facet).
 
-If an **interval** is specified, such as d3.utcDay, **y1** and **y2** can be derived from **y**: *interval*.floor(*y*) is invoked for each *y* to produce *y1*, and *interval*.offset(*y1*) is invoked for each *y1* to produce *y2*. If the interval is specified as a number *n*, *y1* and *y2* are taken as the two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **y1** and **y2** can be derived from **y**: *interval*.floor(*y*) is invoked for each *y* to produce *y1*, and *interval*.offset(*y1*) is invoked for each *y1* to produce *y2*. If the interval is specified as a number *n*, *y1* and *y2* are taken as the two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).

docs/marks/dot.md

@@ -349,7 +349,7 @@ Plot.dotX(cars.map((d) => d["economy (mpg)"]))
 
 Equivalent to [dot](#dot-data-options) except that if the **x** option is not specified, it defaults to the identity function and assumes that *data* = [*x₀*, *x₁*, *x₂*, …].
 
-If an **interval** is specified, such as d3.utcDay, **y** is transformed to (*interval*.floor(*y*) + *interval*.offset(*interval*.floor(*y*))) / 2. If the interval is specified as a number *n*, *y* will be the midpoint of two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **y** is transformed to (*interval*.floor(*y*) + *interval*.offset(*interval*.floor(*y*))) / 2. If the interval is specified as a number *n*, *y* will be the midpoint of two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 ## dotY(*data*, *options*)
 
@@ -359,7 +359,7 @@ Plot.dotY(cars.map((d) => d["economy (mpg)"]))
 
 Equivalent to [dot](#dot-data-options) except that if the **y** option is not specified, it defaults to the identity function and assumes that *data* = [*y₀*, *y₁*, *y₂*, …].
 
-If an **interval** is specified, such as d3.utcDay, **x** is transformed to (*interval*.floor(*x*) + *interval*.offset(*interval*.floor(*x*))) / 2. If the interval is specified as a number *n*, *x* will be the midpoint of two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **x** is transformed to (*interval*.floor(*x*) + *interval*.offset(*interval*.floor(*x*))) / 2. If the interval is specified as a number *n*, *x* will be the midpoint of two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 ## circle(*data*, *options*)
 

docs/marks/frame.md

@@ -115,7 +115,7 @@ The frame mark supports the [standard mark options](../features/marks.md#mark-op
 
 If the **anchor** option is specified as one of *left*, *right*, *top*, or *bottom*, that side is rendered as a single line (and the **fill**, **fillOpacity**, **rx**, and **ry** options are ignored).
 
-## frame(*options*)
+## frame(*options*) {#frame-options-1}
 
 ```js
 Plot.frame({stroke: "red"})

docs/marks/rect.md

@@ -201,7 +201,7 @@ The following channels are optional:
 
 Typically either **x1** and **x2** are specified, or **y1** and **y2**, or both.
 
-If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each **x** to produce **x1**, and *interval*.offset(*x1*) is invoked for each **x1** to produce **x2**. The same is true for **y**, **y1**, and **y2**, respectively. If the interval is specified as a number *n*, **x1** and **x2** are taken as the two consecutive multiples of *n* that bracket **x**. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each **x** to produce **x1**, and *interval*.offset(*x1*) is invoked for each **x1** to produce **x2**. The same is true for **y**, **y1**, and **y2**, respectively. If the interval is specified as a number *n*, **x1** and **x2** are taken as the two consecutive multiples of *n* that bracket **x**. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 The rect mark supports the [standard mark options](../features/marks.md#mark-options), including insets and rounded corners. The **stroke** defaults to *none*. The **fill** defaults to *currentColor* if the stroke is *none*, and to *none* otherwise.
 

docs/marks/rule.md

@@ -135,7 +135,7 @@ Plot.plot({
 ```
 :::
 
-Rules are also used by the [grid mark](./grid) to draw grid lines.
+Rules are also used by the [grid mark](./grid.md) to draw grid lines.
 
 ## Rule options
 
@@ -160,7 +160,7 @@ If **x** is not specified, it defaults to [identity](../features/transforms.md#i
 
 If **y** is specified, it is shorthand for **y2** with **y1** equal to zero; this is the typical configuration for a vertical lollipop chart with rules aligned at *y* = 0. If **y1** is not specified, the rule will start at the top of the plot (or facet). If **y2** is not specified, the rule will end at the bottom of the plot (or facet).
 
-If an **interval** is specified, such as d3.utcDay, **y1** and **y2** can be derived from **y**: *interval*.floor(*y*) is invoked for each *y* to produce *y1*, and *interval*.offset(*y1*) is invoked for each *y1* to produce *y2*. If the interval is specified as a number *n*, *y1* and *y2* are taken as the two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **y1** and **y2** can be derived from **y**: *interval*.floor(*y*) is invoked for each *y* to produce *y1*, and *interval*.offset(*y1*) is invoked for each *y1* to produce *y2*. If the interval is specified as a number *n*, *y1* and *y2* are taken as the two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 ## ruleY(*data*, *options*)
 
@@ -181,4 +181,4 @@ If **y** is not specified, it defaults to [identity](../features/transforms.md#i
 
 If **x** is specified, it is shorthand for **x2** with **x1** equal to zero; this is the typical configuration for a horizontal lollipop chart with rules aligned at *x* = 0. If **x1** is not specified, the rule will start at the left edge of the plot (or facet). If **x2** is not specified, the rule will end at the right edge of the plot (or facet).
 
-If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each *x* to produce *x1*, and *interval*.offset(*x1*) is invoked for each *x1* to produce *x2*. If the interval is specified as a number *n*, *x1* and *x2* are taken as the two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **x1** and **x2** can be derived from **x**: *interval*.floor(*x*) is invoked for each *x* to produce *x1*, and *interval*.offset(*x1*) is invoked for each *x1* to produce *x2*. If the interval is specified as a number *n*, *x1* and *x2* are taken as the two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).

docs/marks/text.md

@@ -256,7 +256,7 @@ Plot.textX(alphabet.map((d) => d.frequency))
 
 Equivalent to [text](#text-data-options), except **x** defaults to [identity](../features/transforms.md#identity) and assumes that *data* = [*x₀*, *x₁*, *x₂*, …].
 
-If an **interval** is specified, such as d3.utcDay, **y** is transformed to (*interval*.floor(*y*) + *interval*.offset(*interval*.floor(*y*))) / 2. If the interval is specified as a number *n*, *y* will be the midpoint of two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **y** is transformed to (*interval*.floor(*y*) + *interval*.offset(*interval*.floor(*y*))) / 2. If the interval is specified as a number *n*, *y* will be the midpoint of two consecutive multiples of *n* that bracket *y*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).
 
 ## textY(*data*, *options*)
 
@@ -266,4 +266,4 @@ Plot.textY(alphabet.map((d) => d.frequency))
 
 Equivalent to [text](#text-data-options), except **y** defaults to [identity](../features/transforms.md#identity) and assumes that *data* = [*y₀*, *y₁*, *y₂*, …].
 
-If an **interval** is specified, such as d3.utcDay, **x** is transformed to (*interval*.floor(*x*) + *interval*.offset(*interval*.floor(*x*))) / 2. If the interval is specified as a number *n*, *x* will be the midpoint of two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales#scale-options).
+If an **interval** is specified, such as d3.utcDay, **x** is transformed to (*interval*.floor(*x*) + *interval*.offset(*interval*.floor(*x*))) / 2. If the interval is specified as a number *n*, *x* will be the midpoint of two consecutive multiples of *n* that bracket *x*. Named UTC intervals such as *day* are also supported; see [scale options](../features/scales.md#scale-options).

test/docs-test.js

@@ -0,0 +1,74 @@
+import assert from "assert";
+import {readdir, readFile, stat} from "fs/promises";
+
+it("documentation links point to existing internal anchors", async () => {
+  const root = "docs";
+
+  // Crawl all files, read their links and anchors.
+  const anchors = new Map();
+  const links = [];
+  for await (const file of readMarkdownFiles(root)) {
+    const text = await readMarkdownSource(root + file);
+    anchors.set(file, getAnchors(text));
+    for (const {pathname, hash} of getLinks(file, text)) {
+      links.push({source: file, target: pathname, hash});
+    }
+  }
+
+  // Check for broken links.
+  let errors = [];
+  for (let {source, target, hash} of links) {
+    if (!target.endsWith(".md")) {
+      errors.push(`- ${source} points to ${target} instead of ${target}.md.`);
+      target += ".md";
+    }
+
+    if (!hash || anchors.get(target).includes(hash.slice(1))) continue;
+    errors.push(`- ${source} points to missing ${target}${hash}.`);
+  }
+  assert(errors.length === 0, new Error(`${errors.length} broken links:\n${errors.join("\n")}`));
+});
+
+// Anchors can be derived from headers, or explicitly written as {#names}.
+function getAnchors(text) {
+  const anchors = [];
+  for (const [, header] of text.matchAll(/^#+ ([*\w][*().,\w\d -]+)\n/gm)) {
+    anchors.push(
+      header
+        .replaceAll(/[^\w\d\s]+/g, " ")
+        .trim()
+        .replaceAll(/ +/g, "-")
+        .toLowerCase()
+    );
+  }
+  for (const [, anchor] of text.matchAll(/ \{#([\w\d-]+)\}/g)) {
+    anchors.push(anchor);
+  }
+  return anchors;
+}
+
+// Internal links.
+function getLinks(file, text) {
+  const links = [];
+  for (const match of text.matchAll(/\[[^\]]+\]\(([^)]+)\)/g)) {
+    const [, link] = match;
+    if (/^\w+:/.test(link)) continue; // absolute link with protocol
+    const {pathname, hash} = new URL(link, new URL(file, "https://example.com/"));
+    links.push({pathname, hash});
+  }
+  return links;
+}
+
+// In source files, ignore comments.
+async function readMarkdownSource(f) {
+  return (await readFile(f, "utf8")).replaceAll(/<!-- .*? -->/gs, "");
+}
+
+// Recursively find all md files in the directory.
+async function* readMarkdownFiles(root, subpath = "/") {
+  for (const fname of await readdir(root + subpath)) {
+    if (fname.startsWith(".") || fname.endsWith(".js")) continue; // ignore .vitepress etc.
+    if ((await stat(root + subpath + fname)).isDirectory()) yield* readMarkdownFiles(root, subpath + fname + "/");
+    else if (fname.endsWith(".md")) yield subpath + fname;
+  }
+}