tauri-apps/tauri · error

Failed to setup custom handlebar template

Error message

Failed to setup custom handlebar template

What it means

When you configure a custom NSIS template, the bundler reads your template file and registers it with the handlebars registry. register_template_string fails if handlebars cannot parse the template (unclosed {{ }}, unknown block syntax, invalid partial), and this expect() panics with 'Failed to setup custom handlebar template'. It means your custom installer template is syntactically invalid as a handlebars template.

Source

Thrown at crates/tauri-bundler/src/bundle/windows/nsis/mod.rs:632

    let mut output = String::new();
    for c in s.chars() {
      match c {
        '\"' => output.push_str("$\\\""),
        '$' => output.push_str("$$"),
        '`' => output.push_str("$\\`"),
        '\n' => output.push_str("$\\n"),
        '\t' => output.push_str("$\\t"),
        '\r' => output.push_str("$\\r"),
        _ => output.push(c),
      }
    }
    output
  });
  if let Some(path) = custom_template_path {
    handlebars
      .register_template_string("installer.nsi", std::fs::read_to_string(path)?)
      .map_err(|e| e.to_string())
      .expect("Failed to setup custom handlebar template");
  } else {
    handlebars
      .register_template_string("installer.nsi", include_str!("./installer.nsi"))
      .map_err(|e| e.to_string())
      .expect("Failed to setup handlebar template");
  }

  write_utf8_with_bom(
    output_path.join("FileAssociation.nsh"),
    include_bytes!("./FileAssociation.nsh"),
  )?;
  write_utf8_with_bom(output_path.join("utils.nsh"), include_bytes!("./utils.nsh"))?;

  let installer_nsi_path = output_path.join("installer.nsi");
  write_utf8_with_bom(
    &installer_nsi_path,
    handlebars.render("installer.nsi", &data)?,
  )?;

View on GitHub (pinned to 52e4b6e71d)

Solutions

1. Open your custom template and find the handlebars syntax error — run `npx handlebars <file>` or an editor with handlebars highlighting to locate unbalanced {{ }} blocks.
2. Diff your custom template against the stock installer.nsi of the exact tauri-bundler version you use (crates/tauri-bundler/src/bundle/windows/nsis/installer.nsi) and re-apply your changes on top of the current stock template.
3. Verify every {{#if}}/{{#each}} has a matching close tag and that variables you reference exist in the data object.
4. Rebuild with `tauri build --bundles nsis`.

Example fix

; before — unclosed block in custom installer.nsi
{{#if installMode}}
  !insertmacro REINSTALL_MODE

; after
{{#if installMode}}
  !insertmacro REINSTALL_MODE
{{/if}}

// CI step: verify the custom NSIS template parses as handlebars before tauri build
// npx --yes handlebars-cli parse installer.nsi  (non-zero exit = syntax error)
fn check_template_balance(src: &str) -> bool {
    let mut depth = 0i32;
    let mut rest = src;
    while let Some(start) = rest.find("{{#") {
        depth += 1;
        rest = &rest[start + 3..];
    }
    depth >= 0
}

When it happens

Trigger: `tauri build --bundles nsis` (Windows) with bundle > windows > nsis > installerHooks / custom template path pointing at a .nsi file containing malformed handlebars syntax — e.g. {{#if x}} without {{/if}}, a stray {{, or template comments that break parsing. The registration at crates/tauri-bundler/src/bundle/windows/nsis/mod.rs:632 maps the parse error to a string and immediately expects success.

Common situations: Editing the copied stock installer.nsi template and breaking a block; upgrading Tauri versions where the expected template variables/blocks changed while your old custom template keeps deprecated syntax; using NSIS `${...}` constructs adjacent to handlebars braces that confuse the parser.

Related errors

• failed to read resource folder name
• Failed to setup custom handlebar template
• Failed to setup handlebar template
• failed to read resource file name
• Failed to render template

AI-assisted analysis of tauri-apps/tauri@52e4b6e71d (2026-08-20). Data as JSON: /api/errors/a96a1843fc3568f1. Report an issue: GitHub.