Add {{fsdocs-meta-tags}} substitution.

docs/_template.html

@@ -14,6 +14,7 @@
     <meta name="twitter:card" content="summary_large_image">
     <meta name="twitter:site" content="{{root}}">
     <meta name="twitter:title" content="{{fsdocs-page-title}}">
+    {{fsdocs-meta-tags}}
     <title>{{fsdocs-page-title}} | {{fsdocs-collection-name}}</title>
     <link href="https://fonts.googleapis.com" rel="preconnect">
     <link crossorigin href="https://fonts.gstatic.com" rel="preconnect">

docs/content.fsx

@@ -70,7 +70,7 @@ Any file or directory beginning with `.` is ignored.
 
 ## Front matter
 
-Each content file can have optional frontmatter.  This determines the navigation bar title, categorization and ordering.
+Each content file can have optional frontmatter.  This determines the navigation bar title, categorization ordering and meta tags.
 
 For markdown, the format is:
 ```
@@ -79,6 +79,8 @@ title: Some Title
 category: Some Category
 categoryindex: 2
 index: 3
+description: Some description
+keywords: tag1, tag2, tag3
 ---
 ```
 For F# scripts the frontmatter is in this form:
@@ -89,13 +91,17 @@ For F# scripts the frontmatter is in this form:
     category: Examples
     categoryindex: 2
     index: 1
+    description: Some description
+    keywords: tag1, tag2, tag3
     ---
     *)
 
 All entries are optional.
 The `categoryindex` determines the ordering of categories.
 The `index` determines the ordering of within each category.
 The `title` is used in the navigation bar instead of any title inferred from the document.
+The `description` is used in `<meta name="description"` as part of the `{{fsdocs-meta-tags}}` substitution.
+The `keywords` are also used in a meta tag as part of `{{fsdocs-meta-tags}}`.
 
 ## Link Translation for Inputs
 
@@ -151,6 +157,7 @@ See [Styling](styling.html) for information about template parameters and stylin
 | `fsdocs-head-extra`           | Additional html content loaded from the `_head.html` file if present in the `--input` folder |
 | `fsdocs-body-extra`           | Additional html content loaded from the `_body.html` file if present in the `--input` folder |
 | `fsdocs-body-class`           | A css class value to help distinguish between `content` and `api-docs` |
+| `fsdocs-meta-tags`            | A set of additional HTML meta tags, present when description and/or keywords are present in the frontmatter |
 
 The following substitutions are extracted from your project files and may or may not be used by the default
 template:

src/FSharp.Formatting.Common/Templating.fs

@@ -204,6 +204,11 @@ module ParamKeys =
     /// This helps to differentiate styles between API docs and custom content.
     let ``fsdocs-body-class`` = ParamKey "fsdocs-body-class"
 
+    /// A parameter key known to FSharp.Formatting, it is HTML composed from additional frontmatter information.
+    /// Such as tags and description
+    /// This can be empty when both properties are not provided for the current page.
+    let ``fsdocs-meta-tags`` = ParamKey "fsdocs-meta-tags"
+
 module internal SimpleTemplating =
 
 #if NETSTANDARD2_0

src/FSharp.Formatting.Literate/Formatting.fs

@@ -143,6 +143,8 @@ module internal Formatting =
         let categoryIndex = findInFrontMatter "categoryindex" |> Option.bind mkValidIndex
         let index = findInFrontMatter "index" |> Option.bind mkValidIndex
         let titleFromFrontMatter = findInFrontMatter "title"
+        let description = findInFrontMatter "description"
+        let tags = findInFrontMatter "keywords"
 
         // If we want to include the source code of the script, then process
         // the entire source and generate replacement {source} => ...some html...
@@ -229,10 +231,26 @@ module internal Formatting =
 
                 getLinksFromCurrentPageIdx currentPageIdx
 
+        let meta =
+            let mkDescription description =
+                $"""<meta name="description" content="%s{description}">
+<meta name="twitter:site" content="%s{description}">
+<meta name="og:description" content="%s{description}">"""
+
+            let mkKeywords keywords =
+                $"""<meta name="keywords" content="%s{keywords}">"""
+
+            match description, tags with
+            | Some description, Some tags -> String.Concat(mkDescription description, "\n", mkKeywords tags)
+            | Some description, None -> mkDescription description
+            | None, Some keywords -> mkKeywords keywords
+            | None, None -> String.Empty
+
         let substitutions0 =
             [ yield ParamKeys.``fsdocs-page-title``, pageTitle
               yield ParamKeys.``fsdocs-page-source``, doc.SourceFile
               yield ParamKeys.``fsdocs-body-class``, "content"
+              yield ParamKeys.``fsdocs-meta-tags``, meta
               yield! ctx.Substitutions
               yield! sourceSubstitutions
               yield! nextPreviousPageSubstitutions ]

tests/FSharp.Literate.Tests/DocContentTests.fs

@@ -1,6 +1,7 @@
 module FSharp.Literate.Tests.DocContent
 
 open System.IO
+open FSharp.Formatting.Templating
 open fsdocs
 open NUnit.Framework
 open FsUnitTyped
@@ -255,6 +256,52 @@ let ``Parses frontmatter correctly `` () =
     twoTowersHtml |> shouldContainText "<a href=\"return.html\">Next</a>"
     returnHtml |> shouldContainText "<a href=\"two-tower.html\">Previous</a>"
 
+[<Test>]
+let ``Parses description and keywords from frontmatter `` () =
+    let rootOutputFolderAsGiven = __SOURCE_DIRECTORY__ </> "output1"
+
+    let relativeInputFolderAsGiven =
+        Path.GetRelativePath(System.Environment.CurrentDirectory, __SOURCE_DIRECTORY__ </> "files")
+
+    if Directory.Exists(rootOutputFolderAsGiven) then
+        Directory.Delete(rootOutputFolderAsGiven, true)
+
+    let content =
+        DocContent(
+            rootOutputFolderAsGiven,
+            Map.empty,
+            lineNumbers = None,
+            evaluate = false,
+            substitutions = [],
+            saveImages = None,
+            watch = false,
+            root = "https://github.com",
+            crefResolver = (fun _ -> None),
+            onError = failwith
+        )
+
+    let docModels = content.Convert(relativeInputFolderAsGiven, None, [])
+
+    let seoPageDocModel =
+        docModels
+        |> List.pick (fun (docInfo, _substitutions) ->
+            match docInfo with
+            | Some(_, _, docModel) when docModel.Title = "StringAnalyzer" -> Some(docModel)
+            | _ -> None)
+
+    let globals = []
+
+    for _thing, action in docModels do
+        action globals
+
+    let meta =
+        seoPageDocModel.Substitutions
+        |> List.find (fst >> ((=) ParamKeys.``fsdocs-meta-tags``))
+        |> snd
+
+    StringAssert.Contains("<meta name=\"description\"", meta)
+    StringAssert.Contains("Great description about StringAnalyzer!", meta)
+    StringAssert.Contains("fsharp, analyzers, tooling", meta)
 
 (* Cannot get this test to evaluate the notebook
 [<Test>]
@@ -283,7 +330,7 @@ let ``ipynb notebook evaluates`` () =
     let globals = []
 
     for (_thing, action) in docModels do
-        action globals  
+        action globals
 
     let ipynbOut = rootOutputFolderAsGiven </> "eval.html" |> File.ReadAllText
 

tests/FSharp.Literate.Tests/FSharp.Literate.Tests.fsproj

@@ -10,6 +10,7 @@
     <None Include="files/simple2.md" />
     <None Include="files/template.html" />
     <None Include="files/docpage.html" />
+    <None Include="files\seo-page.md" />
     <Compile Include="..\Common\MarkdownUnit.fs">
       <Link>Common\MarkdownUnit.fs</Link>
     </Compile>

tests/FSharp.Literate.Tests/files/seo-page.md

@@ -0,0 +1,34 @@
+---
+title: StringAnalyzer
+category: analyzers
+categoryindex: 1
+index: 3
+description: Great description about StringAnalyzer!
+keywords: fsharp, analyzers, tooling
+---
+
+# StringAnalyzer
+
+There are multiple analyzers for various string comparison functions:
+
+- String.EndsWith Analyzer
+- String.StartsWith Analyzer
+- String.IndexOf Analyzer
+
+## Problem
+
+The [recommendations for string usage](https://learn.microsoft.com/en-us/dotnet/standard/base-types/best-practices-strings#recommendations-for-string-usage) mention calling the overloads using `StringComparison` to increase performance.
+
+```fsharp
+"foo".EndsWith("p")
+```
+
+## Fix
+
+Signal your intention explicitly by calling an overload.
+
+```fsharp
+open System
+
+"foo".EndsWith("p", StringComparison.Ordinal)
+```