dynamic loading

content/index.tree

@@ -166,4 +166,4 @@
             - breaking
 
     % content.link = "secret"
-    - this block includes another block's content
+    + this block includes another block's content

crates/treehouse/src/html/mod.rs

@@ -18,3 +18,21 @@ impl<'a> Display for EscapeAttribute<'a> {
         Ok(())
     }
 }
+
+pub struct EscapeHtml<'a>(&'a str);
+
+impl<'a> Display for EscapeHtml<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for c in self.0.chars() {
+            match c {
+                '<' => f.write_str("&lt;")?,
+                '>' => f.write_str("&gt;")?,
+                '&' => f.write_str("&amp;")?,
+                '\'' => f.write_str("&apos;")?,
+                '"' => f.write_str("&quot;")?,
+                _ => f.write_char(c)?,
+            }
+        }
+        Ok(())
+    }
+}

crates/treehouse/src/html/tree.rs

@@ -8,76 +8,37 @@ use crate::{
     state::{toml_error_to_diagnostic, FileId, TomlError, Treehouse},
 };
 
-use super::{attributes::Attributes, markdown};
+use super::{
+    attributes::{Attributes, Content},
+    markdown, EscapeHtml,
+};
 
 pub fn branch_to_html(s: &mut String, treehouse: &mut Treehouse, file_id: FileId, branch: &Branch) {
-    let source = treehouse.get_source(file_id);
-
-    let mut successfully_parsed = true;
-    let mut attributes = if let Some(attributes) = &branch.attributes {
-        toml_edit::de::from_str(&source[attributes.data.clone()]).unwrap_or_else(|error| {
-            treehouse
-                .diagnostics
-                .push(toml_error_to_diagnostic(TomlError {
-                    message: error.message().to_owned(),
-                    span: error.span(),
-                    file_id,
-                    input_range: attributes.data.clone(),
-                }));
-            successfully_parsed = false;
-            Attributes::default()
-        })
-    } else {
-        Attributes::default()
-    };
-    let successfully_parsed = successfully_parsed;
-
-    // Only check for attribute validity if the attributes were parsed successfully.
-    if successfully_parsed {
-        let attribute_warning_span = branch
-            .attributes
-            .as_ref()
-            .map(|attributes| attributes.percent.clone())
-            .unwrap_or(branch.kind_span.clone());
-        if attributes.id.is_empty() {
-            attributes.id = format!("treehouse-missingno-{}", treehouse.next_missingno());
-            treehouse.diagnostics.push(Diagnostic {
-                severity: Severity::Warning,
-                code: Some("attr".into()),
-                message: "branch does not have an `id` attribute".into(),
-                labels: vec![Label {
-                    style: LabelStyle::Primary,
-                    file_id,
-                    range: attribute_warning_span,
-                    message: String::new(),
-                }],
-                notes: vec![
-                    format!(
-                        "note: a generated id `{}` will be used, but this id is unstable and will not persist across generations",
-                        attributes.id
-                    ),
-                    format!("help: run `treehouse fix {}` to add missing ids to branches", treehouse.get_filename(file_id)),
-                ],
-            });
-        }
-    }
+    let attributes = parse_attributes(treehouse, file_id, branch);
 
     // Reborrow because the closure requires unique access (it adds a new diagnostic.)
     let source = treehouse.get_source(file_id);
 
-    let class = if !branch.children.is_empty() {
-        "branch"
+    let has_children =
+        !branch.children.is_empty() || matches!(attributes.content, Content::Link(_));
+
+    let class = if has_children { "branch" } else { "leaf" };
+    let linked_branch = if let Content::Link(link) = &attributes.content {
+        format!(
+            " is=\"th-linked-branch\" data-th-link=\"{}\"",
+            EscapeHtml(link)
+        )
     } else {
-        "leaf"
+        String::new()
     };
     write!(
         s,
-        "<li class=\"{class}\" id=\"{}\">",
+        "<li class=\"{class}\" id=\"{}\"{linked_branch}>",
         EscapeAttribute(&attributes.id)
     )
     .unwrap();
     {
-        if !branch.children.is_empty() {
+        if has_children {
             s.push_str(match branch.kind {
                 BranchKind::Expanded => "<details open>",
                 BranchKind::Collapsed => "<details>",
@@ -110,18 +71,37 @@ pub fn branch_to_html(s: &mut String, treehouse: &mut Treehouse, file_id: FileId
         });
         markdown::push_html(s, markdown_parser);
 
-        s.push_str("<th-bb>");
-        {
+        if let Content::Link(link) = &attributes.content {
             write!(
                 s,
-                "<a class=\"branch-link\" href=\"#{}\" title=\"permalink\"></a>",
+                "<noscript><a class=\"navigate icon-go\" href=\"{}.html\">Go to linked tree: <code>{}</code></a></noscript>",
+                EscapeAttribute(link),
+                EscapeHtml(link),
+            )
+            .unwrap();
+        }
+
+        s.push_str("<th-bb>");
+        {
+            if let Content::Link(link) = &attributes.content {
+                write!(
+                    s,
+                    "<a class=\"icon icon-go\" href=\"{}.html\" title=\"linked tree\"></a>",
+                    EscapeAttribute(link),
+                )
+                .unwrap();
+            }
+
+            write!(
+                s,
+                "<a class=\"icon icon-permalink\" href=\"#{}\" title=\"permalink\"></a>",
                 EscapeAttribute(&attributes.id)
             )
             .unwrap();
         }
         s.push_str("</th-bb>");
 
-        if !branch.children.is_empty() {
+        if has_children {
             s.push_str("</summary>");
             branches_to_html(s, treehouse, file_id, &branch.children);
             s.push_str("</details>");
@@ -132,6 +112,82 @@ pub fn branch_to_html(s: &mut String, treehouse: &mut Treehouse, file_id: FileId
     s.push_str("</li>");
 }
 
+fn parse_attributes(treehouse: &mut Treehouse, file_id: usize, branch: &Branch) -> Attributes {
+    let source = treehouse.get_source(file_id);
+
+    let mut successfully_parsed = true;
+    let mut attributes = if let Some(attributes) = &branch.attributes {
+        toml_edit::de::from_str(&source[attributes.data.clone()]).unwrap_or_else(|error| {
+            treehouse
+                .diagnostics
+                .push(toml_error_to_diagnostic(TomlError {
+                    message: error.message().to_owned(),
+                    span: error.span(),
+                    file_id,
+                    input_range: attributes.data.clone(),
+                }));
+            successfully_parsed = false;
+            Attributes::default()
+        })
+    } else {
+        Attributes::default()
+    };
+    let successfully_parsed = successfully_parsed;
+
+    // Only check for attribute validity if the attributes were parsed successfully.
+    if successfully_parsed {
+        let attribute_warning_span = branch
+            .attributes
+            .as_ref()
+            .map(|attributes| attributes.percent.clone())
+            .unwrap_or(branch.kind_span.clone());
+
+        // Check that every block has an ID.
+        if attributes.id.is_empty() {
+            attributes.id = format!("treehouse-missingno-{}", treehouse.next_missingno());
+            treehouse.diagnostics.push(Diagnostic {
+                severity: Severity::Warning,
+                code: Some("attr".into()),
+                message: "branch does not have an `id` attribute".into(),
+                labels: vec![Label {
+                    style: LabelStyle::Primary,
+                    file_id,
+                    range: attribute_warning_span.clone(),
+                    message: String::new(),
+                }],
+                notes: vec![
+                    format!(
+                        "note: a generated id `{}` will be used, but this id is unstable and will not persist across generations",
+                        attributes.id
+                    ),
+                    format!("help: run `treehouse fix {}` to add missing ids to branches", treehouse.get_filename(file_id)),
+                ],
+            });
+        }
+
+        // Check that link-type blocks are `+`-type to facilitate lazy loading.
+        if let Content::Link(_) = &attributes.content {
+            if branch.kind == BranchKind::Expanded {
+                treehouse.diagnostics.push(Diagnostic {
+                    severity: Severity::Warning,
+                    code: Some("attr".into()),
+                    message: "`content.link` branch is expanded by default".into(),
+                    labels: vec![Label {
+                        style: LabelStyle::Primary,
+                        file_id,
+                        range: branch.kind_span.clone(),
+                        message: String::new(),
+                    }],
+                    notes: vec![
+                        "note: `content.link` branches should normally be collapsed to allow for lazy loading".into(),
+                    ],
+                });
+            }
+        }
+    }
+    attributes
+}
+
 pub fn branches_to_html(
     s: &mut String,
     treehouse: &mut Treehouse,

static/css/tree.css

@@ -97,8 +97,7 @@
     opacity: 100%;
 }
 
-.tree .branch-link {
-    background-image: url("../svg/link.svg");
+.tree .icon {
     background-repeat: no-repeat;
     background-position: 50% 50%;
     opacity: 35%;
@@ -106,3 +105,24 @@
     width: 24px;
     height: 24px;
 }
+
+.tree .icon-permalink {
+    background-image: url("../svg/permalink.svg");
+}
+
+.tree .icon-go {
+    background-image: url("../svg/go.svg");
+}
+
+.tree a.navigate {
+    background-repeat: no-repeat;
+    background-position: 0 50%;
+    opacity: 50%;
+    color: #000;
+    padding-left: 20px;
+}
+
+.tree .link-loading {
+    padding-left: 24px;
+    opacity: 50%;
+}

static/js/tree.js

@@ -0,0 +1,60 @@
+class LinkedBranch extends HTMLLIElement {
+    constructor() {
+        super();
+
+        this.linkedTree = this.getAttribute("data-th-link");
+
+        this.details = this.childNodes[0];
+        this.innerUL = this.details.childNodes[1];
+
+        this.state = "notloaded";
+
+        this.loadingText = document.createElement("p");
+        {
+            this.loadingText.className = "link-loading";
+            let linkedTreeName = document.createElement("code");
+            linkedTreeName.innerText = this.linkedTree;
+            this.loadingText.append("Loading ", linkedTreeName, "...");
+        }
+        this.innerUL.appendChild(this.loadingText);
+
+        // This produces a warning during static generation but we still want to handle that
+        // correctly. Having an expanded-by-default linked block can be useful in development.
+        if (this.details.open) {
+            this.loadTree();
+        }
+
+        this.details.addEventListener("toggle", event => {
+            if (this.details.open) {
+                this.loadTree();
+            }
+        });
+    }
+
+    loadTree() {
+        if (this.state == "notloaded") {
+            this.state = "loading";
+
+            fetch(`/${this.linkedTree}.html`)
+                .then(request => request.text())
+                .then(text => {
+                    let parser = new DOMParser();
+                    let linkedDocument = parser.parseFromString(text, "text/html");
+                    let main = linkedDocument.getElementsByTagName("main")[0];
+                    let ul /*: Element */ = main.getElementsByTagName("ul")[0];
+                    console.log(ul);
+
+                    this.loadingText.remove();
+
+                    for (let i = 0; i < ul.childNodes.length; ++i) {
+                        this.innerUL.appendChild(ul.childNodes[i]);
+                    }
+                })
+                .catch(error => {
+                    this.loadingText.innerText = error.toString();
+                });
+        }
+    }
+}
+
+customElements.define("th-linked-branch", LinkedBranch, { extends: "li" });

template/tree.hbs

@@ -11,6 +11,7 @@
     <link rel="stylesheet" href="{{ site }}/static/css/tree.css">
     <link rel="stylesheet" href="{{ site }}/static/font/font.css">
 
+    <script type="module" src="{{ site }}/static/js/tree.js"></script>
     <script type="module" src="{{ site }}/static/js/usability.js"></script>
 </head>