feat: support line number checking in link fragment (e.g: '#L50')

Fixes #6

src/index.js

@@ -8,6 +8,9 @@ const {
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
   getMarkdownIdOrAnchorNameFragments,
+  isValidIntegerString,
+  getNumberOfLines,
+  getLineNumberStringFromFragment,
 } = require("./utils.js")
 
 /** @typedef {import('markdownlint').Rule} MarkdownLintRule */
@@ -121,7 +124,35 @@ const customRule = {
 
         fragmentsHTML.push(...idOrAnchorNameHTMLFragments)
 
-        if (!fragmentsHTML.includes(url.hash)) {
+        if (!fragmentsHTML.includes(url.hash.toLowerCase())) {
+          if (url.hash.startsWith("#L")) {
+            const lineNumberFragmentString = getLineNumberStringFromFragment(
+              url.hash,
+            )
+
+            const hasOnlyDigits = isValidIntegerString(lineNumberFragmentString)
+            if (!hasOnlyDigits) {
+              onError({
+                lineNumber,
+                detail: `${detail} should have a valid fragment identifier`,
+              })
+              continue
+            }
+
+            const lineNumberFragment = Number.parseInt(
+              lineNumberFragmentString,
+              10,
+            )
+            const numberOfLines = getNumberOfLines(fileContent)
+            if (lineNumberFragment > numberOfLines) {
+              onError({
+                lineNumber,
+                detail: `${detail} should have a valid fragment identifier, ${detail} should have at least ${lineNumberFragment} lines to be valid`,
+              })
+              continue
+            }
+          }
+
           onError({
             lineNumber,
             detail: `${detail} should have a valid fragment identifier`,

src/utils.js

@@ -114,8 +114,47 @@ const getMarkdownIdOrAnchorNameFragments = (content) => {
   return result
 }
 
+/**
+ * Checks if a string is a valid integer.
+ *
+ * Using `Number.parseInt` combined with `Number.isNaN` will not be sufficient enough because `Number.parseInt("1abc", 10)` will return `1` (a valid number) instead of `NaN`.
+ *
+ * @param {string} value
+ * @returns {boolean}
+ * @example isValidIntegerString("1") // true
+ * @example isValidIntegerString("45") // true
+ * @example isValidIntegerString("1abc") // false
+ * @example isValidIntegerString("1.0") // false
+ */
+const isValidIntegerString = (value) => {
+  const regex = /^\d+$/
+  return regex.test(value)
+}
+
+/**
+ * Gets the number of lines in a string, based on the number of `\n` characters.
+ * @param {string} content
+ * @returns {number}
+ */
+const getNumberOfLines = (content) => {
+  return content.split("\n").length
+}
+
+/**
+ * Gets the line number string from a fragment.
+ * @param {string} fragment
+ * @returns {string}
+ * @example getLineNumberStringFromFragment("#L50") // 50
+ */
+const getLineNumberStringFromFragment = (fragment) => {
+  return fragment.slice(2)
+}
+
 module.exports = {
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
   getMarkdownIdOrAnchorNameFragments,
+  isValidIntegerString,
+  getNumberOfLines,
+  getLineNumberStringFromFragment,
 }

test/fixtures/invalid/invalid-heading-with-L-fragment/awesome.md

@@ -0,0 +1 @@
+# Awesome

test/fixtures/invalid/invalid-heading-with-L-fragment/invalid-heading-with-L-fragment.md

@@ -0,0 +1,3 @@
+# Invalid
+
+[Link fragment line number 7](./awesome.md#L7abc)

test/fixtures/invalid/invalid-line-number-fragment/awesome.md

@@ -0,0 +1 @@
+# Awesome

test/fixtures/invalid/invalid-line-number-fragment/invalid-line-number-fragment.md

@@ -0,0 +1,3 @@
+# Invalid
+
+[Link fragment line number 7](./awesome.md#L7)

test/fixtures/valid/existing-heading-case-insensitive/awesome.md

@@ -0,0 +1,3 @@
+# Awesome
+
+## Existing Heading

test/fixtures/valid/existing-heading-case-insensitive/existing-heading-case-insensitive.md

@@ -0,0 +1,3 @@
+# Valid
+
+[Link fragment](./awesome.md#ExistIng-Heading)

test/fixtures/valid/existing-heading-fragment/awesome.md

@@ -1,4 +1,4 @@
-# Valid
+# Awesome
 
 ## Existing Heading
 

test/fixtures/valid/valid-heading-like-number-fragment/awesome.md

@@ -0,0 +1,3 @@
+# Awesome
+
+## L7

test/fixtures/valid/valid-heading-like-number-fragment/valid-heading-like-number-fragment.md

@@ -0,0 +1,3 @@
+# Valid
+
+[Link fragment](./awesome.md#L7)

test/fixtures/valid/valid-line-number-fragment/awesome.md

@@ -0,0 +1,9 @@
+# Awesome
+
+ABC
+
+Line 5
+
+Line 7 Text
+
+## L7

test/fixtures/valid/valid-line-number-fragment/valid-line-number-fragment.md

@@ -0,0 +1,3 @@
+# Valid
+
+[Link fragment line number 7](./awesome.md#L7)

test/index.test.js

@@ -45,6 +45,19 @@ test("ensure the rule validates correctly", async (t) => {
         error:
           '"./awesome.md#not-an-id-should-be-ignored" should have a valid fragment identifier',
       },
+      {
+        name: "with invalid heading with #L fragment",
+        fixturePath:
+          "test/fixtures/invalid/invalid-heading-with-L-fragment/invalid-heading-with-L-fragment.md",
+        error: '"./awesome.md#L7abc" should have a valid fragment identifier',
+      },
+      {
+        name: "with a invalid line number fragment",
+        fixturePath:
+          "test/fixtures/invalid/invalid-line-number-fragment/invalid-line-number-fragment.md",
+        error:
+          '"./awesome.md#L7" should have a valid fragment identifier, "./awesome.md#L7" should have at least 7 lines to be valid',
+      },
       {
         name: "with a non-existing anchor name fragment",
         fixturePath:
@@ -118,6 +131,11 @@ test("ensure the rule validates correctly", async (t) => {
         fixturePath:
           "test/fixtures/valid/existing-element-id-fragment/existing-element-id-fragment.md",
       },
+      {
+        name: "with an existing heading fragment (case insensitive)",
+        fixturePath:
+          "test/fixtures/valid/existing-heading-case-insensitive/existing-heading-case-insensitive.md",
+      },
       {
         name: "with an existing heading fragment",
         fixturePath:
@@ -128,6 +146,16 @@ test("ensure the rule validates correctly", async (t) => {
         fixturePath:
           "test/fixtures/valid/only-parse-markdown-files-for-fragments/only-parse-markdown-files-for-fragments.md",
       },
+      {
+        name: 'with valid heading "like" line number fragment',
+        fixturePath:
+          "test/fixtures/valid/valid-heading-like-number-fragment/valid-heading-like-number-fragment.md",
+      },
+      {
+        name: "with valid line number fragment",
+        fixturePath:
+          "test/fixtures/valid/valid-line-number-fragment/valid-line-number-fragment.md",
+      },
       {
         name: "with an existing file",
         fixturePath: "test/fixtures/valid/existing-file.md",

test/utils.test.js

@@ -5,6 +5,9 @@ const {
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
   getMarkdownIdOrAnchorNameFragments,
+  isValidIntegerString,
+  getNumberOfLines,
+  getLineNumberStringFromFragment,
 } = require("../src/utils.js")
 
 test("utils", async (t) => {
@@ -54,4 +57,23 @@ test("utils", async (t) => {
     assert.deepStrictEqual(getMarkdownIdOrAnchorNameFragments("<a>"), [])
     assert.deepStrictEqual(getMarkdownIdOrAnchorNameFragments("<a id=>"), [])
   })
+
+  await t.test("isValidIntegerString", async () => {
+    assert.strictEqual(isValidIntegerString("1"), true)
+    assert.strictEqual(isValidIntegerString("45"), true)
+    assert.strictEqual(isValidIntegerString("1abc"), false)
+    assert.strictEqual(isValidIntegerString("1.0"), false)
+  })
+
+  await t.test("getNumberOfLines", async () => {
+    assert.strictEqual(getNumberOfLines(""), 1)
+    assert.strictEqual(getNumberOfLines("Hello"), 1)
+    assert.strictEqual(getNumberOfLines("Hello\nWorld"), 2)
+    assert.strictEqual(getNumberOfLines("Hello\nWorld\n"), 3)
+    assert.strictEqual(getNumberOfLines("Hello\nWorld\n\n"), 4)
+  })
+
+  await t.test("getLineNumberStringFromFragment", async () => {
+    assert.strictEqual(getLineNumberStringFromFragment("#L50"), "50")
+  })
 })