Add shortcode 'invocation' variable to allow a shortcode to track how… (#1236)

* add shortcode 'invocation' variable to allow a shortcode to track how many times it has been invoked in a given Markdown file

* use closure (implicit struct) instead of explicit struct for invocation tracking

* update variable name to "nth"

components/rendering/src/shortcode.rs

@@ -3,6 +3,7 @@ use pest::iterators::Pair;
 use pest::Parser;
 use pest_derive::Parser;
 use regex::Regex;
+use std::collections::HashMap;
 use tera::{to_value, Context, Map, Value};
 
 use crate::context::RenderContext;
@@ -102,6 +103,7 @@ fn render_shortcode(
     name: &str,
     args: &Map<String, Value>,
     context: &RenderContext,
+    invocation_count: u32,
     body: Option<&str>,
 ) -> Result<String> {
     let mut tera_context = Context::new();
@@ -112,6 +114,7 @@ fn render_shortcode(
         // Trimming right to avoid most shortcodes with bodies ending up with a HTML new line
         tera_context.insert("body", b.trim_end());
     }
+    tera_context.insert("nth", &invocation_count);
     tera_context.extend(context.tera_context.clone());
 
     let mut template_name = format!("shortcodes/{}.md", name);
@@ -139,6 +142,12 @@ fn render_shortcode(
 
 pub fn render_shortcodes(content: &str, context: &RenderContext) -> Result<String> {
     let mut res = String::with_capacity(content.len());
+    let mut invocation_map: HashMap<String, u32> = HashMap::new();
+    let mut get_invocation_count = |name: &str| {
+        let invocation_number = invocation_map.entry(String::from(name)).or_insert(0);
+        *invocation_number += 1;
+        *invocation_number
+    };
 
     let mut pairs = match ContentParser::parse(Rule::page, content) {
         Ok(p) => p,
@@ -184,7 +193,13 @@ pub fn render_shortcodes(content: &str, context: &RenderContext) -> Result<Strin
             Rule::text => res.push_str(p.as_span().as_str()),
             Rule::inline_shortcode => {
                 let (name, args) = parse_shortcode_call(p);
-                res.push_str(&render_shortcode(&name, &args, context, None)?);
+                res.push_str(&render_shortcode(
+                    &name,
+                    &args,
+                    context,
+                    get_invocation_count(&name),
+                    None,
+                )?);
             }
             Rule::shortcode_with_body => {
                 let mut inner = p.into_inner();
@@ -192,7 +207,13 @@ pub fn render_shortcodes(content: &str, context: &RenderContext) -> Result<Strin
                 // we don't care about the closing tag
                 let (name, args) = parse_shortcode_call(inner.next().unwrap());
                 let body = inner.next().unwrap().as_span().as_str();
-                res.push_str(&render_shortcode(&name, &args, context, Some(body))?);
+                res.push_str(&render_shortcode(
+                    &name,
+                    &args,
+                    context,
+                    get_invocation_count(&name),
+                    Some(body),
+                )?);
             }
             Rule::ignored_inline_shortcode => {
                 res.push_str(

components/rendering/tests/markdown.rs

@@ -1059,6 +1059,36 @@ fn emoji_aliases_are_ignored_when_disabled_in_config() {
     assert_eq!(res.body, "<p>Hello, World! :smile:</p>\n");
 }
 
+#[test]
+fn invocation_count_increments_in_shortcode() {
+    let permalinks_ctx = HashMap::new();
+    let mut tera = Tera::default();
+    tera.extend(&ZOLA_TERA).unwrap();
+
+    let shortcode_template_a = r#"<p>a: {{ nth }}</p>"#;
+    let shortcode_template_b = r#"<p>b: {{ nth }}</p>"#;
+
+    let markdown_string = r#"{{ a() }}
+{{ b() }}
+{{ a() }}
+{{ b() }}
+"#;
+
+    let expected = r#"<p>a: 1</p>
+<p>b: 1</p>
+<p>a: 2</p>
+<p>b: 2</p>
+"#;
+
+    tera.add_raw_template("shortcodes/a.html", shortcode_template_a).unwrap();
+    tera.add_raw_template("shortcodes/b.html", shortcode_template_b).unwrap();
+    let config = Config::default();
+    let context = RenderContext::new(&tera, &config, "", &permalinks_ctx, InsertAnchor::None);
+
+    let res = render_content(markdown_string, &context).unwrap();
+    assert_eq!(res.body, expected);
+}
+
 #[test]
 fn basic_external_links_unchanged() {
     let permalinks_ctx = HashMap::new();

docs/content/documentation/content/shortcodes.md

@@ -134,6 +134,24 @@ If you want to have some content that looks like a shortcode but not have Zola t
 you will need to escape it by using `{%/*` and `*/%}` instead of `{%` and `%}`. You won't need to escape
 anything else until the closing tag.
 
+### Invocation Count
+
+Every shortcode context is passed in a variable named `nth` that tracks how many times a particular shortcode has
+been invoked in a Markdown file. Given a shortcode `true_statement.html` template:
+
+```jinja2
+<p id="number{{ nth }}">{{ value }} is equal to {{ nth }}.</p>
+```
+
+It could be used in our Markdown as follows:
+
+```md
+{{/* true_statement(value=1) */}}
+{{/* true_statement(value=2) */}}
+```
+
+This is useful when implementing custom markup for features such as sidenotes or end notes.
+
 ## Built-in shortcodes
 
 Zola comes with a few built-in shortcodes. If you want to override a default shortcode template,