GitHub Actions: Check URLs using lychee

This makes it possible to be aware of dead links and replace
them with other resources (such as archived versions) as
soon as possible.

.github/workflows/check_urls.yml

@@ -0,0 +1,31 @@
+name: 🌐 Check URLs
+on:
+  push:
+  pull_request:
+  schedule:
+    # Every day at midnight (UTC).
+    # URLs can decay over time. Setting up a schedule makes it possible to be warned
+    # about dead links as soon as possible.
+    - cron: "0 18 * * *"
+
+jobs:
+  check-urls:
+    runs-on: ubuntu-24.04
+    steps:
+
+      - uses: actions/checkout@v4
+
+      - name: Restore lychee cache
+        uses: actions/cache@v4
+        with:
+          path: .lycheecache
+          key: cache-lychee-${{ github.sha }}
+          restore-keys: cache-lychee-
+
+      - name: Run lychee
+        uses: lycheeverse/lychee-action@v2
+        with:
+          args: --base . --verbose --no-progress --cache --max-cache-age 1d --exclude-path _templates/ "**/*.md" "**/*.html" "**/*.rst"
+
+      - name: Fail if there were link errors
+        run: exit ${{ steps.lc.outputs.exit_code }}

.lycheeignore

@@ -0,0 +1,25 @@
+# Don't read Godot's own URL schemes as web URLs.
+user://.*
+res://.*
+
+# Don't read WebSockets URLs as web URLs.
+wss://.*
+
+# Security checks prevent checking the URLs of these websites automatically,
+# typically returning 403 errors.
+.*asecuritysite\.com.*
+.*intel\.com.*
+.*reddit\.com.*
+
+# Don't check URLs from these websites due to frequent rate limits (error 429) or timeouts.
+.*adobe\.com.*
+.*github\.com.*
+.*gnu\.org.*
+.*meta\.com.*
+
+# Not a valid URL with the GET method, which lychee always sends.
+# Mentioned in the class reference.
+.*httpbin\.org/post
+
+# Class reference metnions `example.com/index.php` in an example, which is 404.
+.*example\.com.*

tutorials/shaders/shader_reference/shader_functions.rst

@@ -287,7 +287,7 @@ Trigonometric function descriptions
 
     :return:
         The angle whose trigonometric cosine is ``x``.
-        
+
     https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/acos.xhtml
 
 .. rst-class:: classref-item-separator
@@ -795,7 +795,7 @@ Exponential and math function descriptions
 
     |componentwise|
 
-    Returns the absolute value of ``x``. Returns ``x`` if ``x`` is positive, otherwise returns ``-1 * x``. 
+    Returns the absolute value of ``x``. Returns ``x`` if ``x`` is positive, otherwise returns ``-1 * x``.
 
     :param x:
         The value of which to return the absolute.
@@ -872,7 +872,7 @@ Exponential and math function descriptions
 
     .. note::
         Rounding of values with a fractional part of ``0.5`` is implementation-dependent.
-        This includes the possibility that ``round(x)`` returns the same value as 
+        This includes the possibility that ``round(x)`` returns the same value as
         ``roundEven(x)``for all values of ``x``.
 
     :param x:
@@ -2911,7 +2911,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative of ``p``.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/dFdxCoarse.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/dFdx.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -2946,7 +2946,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative of ``p``.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/dFdxFine.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/dFdx.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -2981,7 +2981,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative of ``p``.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/dFdy.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/dFdx.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -3016,7 +3016,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative of ``p``.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/dFdyCoarse.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/dFdx.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -3049,7 +3049,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative of ``p``.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/dFdyFine.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/dFdx.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -3107,7 +3107,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/fwidthCoarse.xhtml
+    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/fwidth.xhtml
 
 .. rst-class:: classref-item-separator
 
@@ -3138,7 +3138,7 @@ vec4 **textureGather**\ (\ samplerCube s, vec3 p [, int comps] ) :ref:`🔗<shad
     :return:
         The partial derivative.
 
-    https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/fwidthFine.xhtml
+    https://registry.khronos.org/OpenGL-Refpages/gl4/html/fwidth.xhtml
 
 
 .. rst-class:: classref-section-separator
@@ -3566,7 +3566,7 @@ Bitwise function descriptions
 
     .. warning::
         The result will be undefined if:
-        
+
         - offset or bits is negative.
         - if the sum of offset and bits is greater than the number of bits used to store the operand.