CLI: Support more page number templates in output file name (#3933)

crates/typst-cli/src/args.rs

@@ -68,7 +68,11 @@ pub struct CompileCommand {
     #[clap(flatten)]
     pub common: SharedArgs,
 
-    /// Path to output file (PDF, PNG, or SVG), use `-` to write output to stdout
+    /// Path to output file (PDF, PNG, or SVG).
+    /// Use `-` to write output to stdout; For output formats emitting one file per page,
+    /// a page number template must be present if the source document renders to multiple pages.
+    /// Use `{p}` for page numbers, `{0p}` for zero padded page numbers, `{t}` for page count.
+    /// For example, `doc-page-{0p}-of-{t}.png` creates `doc-page-01-of-10.png` and so on.
     #[clap(required_if_eq("input", "-"), value_parser = ValueParser::new(output_value_parser))]
     pub output: Option<Output>,
 

crates/typst-cli/src/compile.rs

@@ -206,25 +206,24 @@ fn export_image(
     watching: bool,
     fmt: ImageExportFormat,
 ) -> StrResult<()> {
-    // Determine whether we have a `{n}` numbering.
     let output = command.output();
+    // Determine whether we have indexable templates in output
     let can_handle_multiple = match output {
         Output::Stdout => false,
-        Output::Path(ref output) => output.to_str().unwrap_or_default().contains("{n}"),
+        Output::Path(ref output) => {
+            output_template::has_indexable_template(output.to_str().unwrap_or_default())
+        }
     };
     if !can_handle_multiple && document.pages.len() > 1 {
-        let s = match output {
+        let err = match output {
             Output::Stdout => "to stdout",
-            Output::Path(_) => "without `{n}` in output path",
+            Output::Path(_) => {
+                "without a page number template ({p}, {0p}) in the output path"
+            }
         };
-        bail!("cannot export multiple images {s}");
+        bail!("cannot export multiple images {err}");
     }
 
-    // Find a number width that accommodates all pages. For instance, the
-    // first page should be numbered "001" if there are between 100 and
-    // 999 pages.
-    let width = 1 + document.pages.len().checked_ilog10().unwrap_or(0) as usize;
-
     let cache = world.export_cache();
 
     // The results are collected in a `Vec<()>` which does not allocate.
@@ -238,10 +237,11 @@ fn export_image(
                 Output::Path(ref path) => {
                     let storage;
                     let path = if can_handle_multiple {
-                        storage = path
+                        storage = output_template::format(
-                            .to_str()
+                            path.to_str().unwrap_or_default(),
-                            .unwrap_or_default()
+                            i + 1,
-                            .replace("{n}", &format!("{:0width$}", i + 1));
+                            document.pages.len(),
+                        );
                         Path::new(&storage)
                     } else {
                         path
@@ -267,6 +267,35 @@ fn export_image(
     Ok(())
 }
 
+mod output_template {
+    const INDEXABLE: [&str; 3] = ["{p}", "{0p}", "{n}"];
+
+    pub fn has_indexable_template(output: &str) -> bool {
+        INDEXABLE.iter().any(|template| output.contains(template))
+    }
+
+    pub fn format(output: &str, this_page: usize, total_pages: usize) -> String {
+        // Find the base 10 width of number `i`
+        fn width(i: usize) -> usize {
+            1 + i.checked_ilog10().unwrap_or(0) as usize
+        }
+
+        let other_templates = ["{t}"];
+        INDEXABLE.iter().chain(other_templates.iter()).fold(
+            output.to_string(),
+            |out, template| {
+                let replacement = match *template {
+                    "{p}" => format!("{this_page}"),
+                    "{0p}" | "{n}" => format!("{:01$}", this_page, width(total_pages)),
+                    "{t}" => format!("{total_pages}"),
+                    _ => unreachable!("unhandled template placeholder {template}"),
+                };
+                out.replace(template, replacement.as_str())
+            },
+        )
+    }
+}
+
 /// Export single image.
 fn export_image_page(
     command: &CompileCommand,