tools/create/src/main.rs

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

mod template_helpers;
mod util;

#[cfg(test)]
mod test_util;

use anyhow::{anyhow, bail, Context};
use argh::FromArgs;
use chrono::{Datelike, Utc};
use handlebars::Handlebars;
use serde::Serialize;
use std::collections::HashMap;
use std::path::{Component, Path, PathBuf};
use std::str::FromStr;
use std::{fmt, fs, io};
use termion::{color, style};

const LANG_AGNOSTIC_EXTENSION: &'static str = "tmpl";

fn main() -> Result<(), anyhow::Error> {
    let args: CreateArgs = argh::from_env();
    let templates_dir_path = util::get_templates_dir_path()?;

    // Get the list of template file paths available to this project type and language.
    let template_files = find_template_files(
        &templates_dir_path.join("templates.json"),
        &args.project_template()?,
        &args.lang,
        &StdFs,
    )?;

    // Collect the template files for this project type and language.
    let template_tree = TemplateTree::from_file_list(
        &templates_dir_path,
        &template_files,
        &args.project_template()?,
        &StdFs,
    )?;

    // Register the template engine.
    let mut handlebars = Handlebars::new();
    handlebars.set_strict_mode(true);
    template_helpers::register_helpers(&mut handlebars);

    // Register partial templates.
    register_partial_templates(&mut handlebars, &templates_dir_path, &template_files, &StdFs)?;

    // Create the set of variables accessible to template files.
    let template_args = TemplateArgs::from_create_args(&args)?;

    // Execute the templates and render them to an in-memory representation.
    let project = template_tree.render(&mut handlebars, &template_args)?;

    // Ensure the destination doesn't exist.
    let dest_project_path = args.absolute_project_path()?;
    if dest_project_path.exists() {
        bail!("project directory already exists: {}", dest_project_path.display());
    }

    // Create the directories leading to this project.
    fs::create_dir_all(&args.project_path.project_parent)?;

    // Write the rendered files..
    project.write(&dest_project_path)?;

    if !args.silent {
        let project_name = &args.project_path.project_name;
        println!("Project created at {}.", dest_project_path.display());

        // Find the parent BUILD.gn file and suggest adding the test target.
        let parent_build =
            dest_project_path.parent().map(|p| p.join("BUILD.gn")).filter(|b| b.exists());
        if let Some(parent_build) = parent_build {
            println!(
                "{}note:{} Don't forget to include the {}{}:tests{} GN target in the parent {}tests{} target ({}).",
                color::Fg(color::Yellow), color::Fg(color::Reset),
                style::Bold, project_name, style::Reset,
                style::Bold, style::Reset,
                parent_build.display()
            );
        }
    }

    Ok(())
}

/// Creates scaffolding for new projects.
#[derive(Debug, FromArgs)]
#[argh(
    name = "fx-create",
    description = "Creates scaffolding for new projects.",
    note = "Create a new project scaffold based on templates for Fuchsia software.

The last segment of the project path represents the project name and will be
used as the GN build target name. GN-style paths are supported (//src/sys).
The last segment of the path must start with an alphabetic character and be
followed by zero or more alphanumeric characters, or the `-` character.",
    example = "To create a new component project:
    $ fx create component --path <project-path> --lang rust

Supports the following project types:
    create component          # CML-based component launched by Component Manager
    create component test     # Integration test component
    create driver             # Driver launched in a devhost
    create devicetree visitor # Visitor for devicetree parsing"
)]
struct CreateArgs {
    /// type of the newly created project.
    #[argh(positional)]
    project_type: String,

    /// optional subtype. If not provided, the subtype is 'default'.
    #[argh(positional, default = "String::from(\"default\")")]
    project_subtype: String,

    /// destination path for the new project.
    #[argh(option, long = "path")]
    project_path: ProjectPath,

    /// programming language for the new project.
    /// Supported options: 'rust', 'cpp'
    #[argh(option)]
    lang: Language,

    /// override for the project include path. For testing.
    #[argh(option)]
    override_project_path: Option<PathBuf>,

    /// override the copyright year. For testing.
    #[argh(option)]
    override_copyright_year: Option<u32>,

    /// when set, do not emit anything to stdout.
    #[argh(switch)]
    silent: bool,
}

/// A project path pointing to a non-existent leaf directory which
/// will be the home of the new project. The project name is derived
/// from the leaf directory.
#[derive(PartialEq, Eq, Debug, Clone)]
struct ProjectPath {
    project_parent: PathBuf,
    project_name: String,
}

impl FromStr for ProjectPath {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        // First handle a GN absolute path (//foo/bar).
        let path = if s.starts_with("//") {
            util::get_fuchsia_root()?.join(Path::new(&s[2..]))
        } else {
            PathBuf::from(s)
        };
        let project_parent = {
            let mut parent = path.parent().expect("parent should never be None");
            if parent == Path::new("") {
                parent = Path::new(".");
            }
            if parent.is_absolute() {
                parent.to_path_buf()
            } else {
                std::env::current_dir()?.join(parent)
            }
        };
        let project_name =
            util::filename_to_string(path.file_name().with_context(|| "missing project name")?)?;
        let mut chars_iter = project_name.chars();
        if !chars_iter.next().with_context(|| "project name is empty")?.is_alphabetic() {
            return Err(anyhow!("project name must start with an alphabetic character"));
        }
        if chars_iter.any(|c| !c.is_alphanumeric() && c != '-') {
            return Err(anyhow!("project name must only contain alphanumeric characters and `-`"));
        }
        Ok(ProjectPath { project_parent, project_name })
    }
}

impl CreateArgs {
    /// Returns the absolute path to the new project.
    fn absolute_project_path(&self) -> io::Result<PathBuf> {
        Ok(self.project_path.project_parent.join(&self.project_path.project_name))
    }

    /// Returns the template name of the project type
    fn project_template(&self) -> io::Result<String> {
        Ok(format!("{}-{}", self.project_type, self.project_subtype))
    }
}

/// Supported languages for project creation.
#[derive(Debug)]
enum Language {
    Rust,
    Cpp,
}

impl Language {
    /// Returns the language's template extension. Template
    /// files that match this extension belong to this language.
    fn template_extension(&self) -> &'static str {
        match self {
            Self::Rust => "tmpl-rust",
            Self::Cpp => "tmpl-cpp",
        }
    }

    // Check if the file's extension matches the language-specific template
    // extension or the general template extension.
    fn matches(&self, path: &Path) -> bool {
        if let Some(ext) = path.extension() {
            ext == self.template_extension() || ext == LANG_AGNOSTIC_EXTENSION
        } else {
            false
        }
    }
}

impl FromStr for Language {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Ok(match s {
            "rust" => Self::Rust,
            "cpp" => Self::Cpp,
            _ => return Err(format!("unrecognized language \"{}\"", s)),
        })
    }
}

impl fmt::Display for Language {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match self {
            Self::Rust => "rust",
            Self::Cpp => "cpp",
        })
    }
}

/// Given a path to a JSON file, extract a list of template files that match the
/// `project_type` and `lang`.
///
/// The JSON file must consist of a root list of strings, where each string is a path relative
/// to the directory that contains the JSON file.
///
/// E.g.
///
/// `out/default/host-tools/create_templates/templates.json`:
/// ```json
/// [
///     "component-default/BUILD.gn.tmpl-rust",
///     "component-default/src/main.rs.tmpl-rust"
/// ]
/// ```
///
/// This file is generated by the GN build rule in //tools/create/templates/BUILD.gn.
fn find_template_files<FR>(
    json_file: &Path,
    project_type: &str,
    lang: &Language,
    file_reader: &FR,
) -> Result<Vec<PathBuf>, anyhow::Error>
where
    FR: FileReader,
{
    let json_contents = file_reader.read_to_string(json_file)?;
    let template_files: Vec<PathBuf> = serde_json::from_slice(json_contents.as_bytes())?;
    let mut template_files: Vec<PathBuf> = template_files
        .into_iter()
        .filter(|p| {
            lang.matches(p)
                && (p.starts_with(project_type) || (is_partial_template(p) && is_root_file(p)))
        })
        .collect();
    template_files.sort();
    Ok(template_files)
}

/// Returns true if this path is a single segment path, e.g. "foo.txt".
fn is_root_file(path: &Path) -> bool {
    let mut iter = path.components();
    match iter.next() {
        Some(Component::Normal(_)) => iter.next().is_none(),
        _ => false,
    }
}

/// Returns true if the template file name begins with an `_`.
fn is_partial_template(path: impl AsRef<Path>) -> bool {
    path.as_ref()
        .file_name()
        .and_then(std::ffi::OsStr::to_str)
        .map(|f| f.starts_with('_'))
        .unwrap_or(false)
}

/// Registers any partial templates (templates whose file names begin with `_`) with the templating
/// engine.
fn register_partial_templates<FR>(
    handlebars: &mut Handlebars<'_>,
    templates_dir: &Path,
    template_files: &Vec<PathBuf>,
    file_reader: &FR,
) -> Result<(), anyhow::Error>
where
    FR: FileReader,
{
    for partial in template_files.into_iter().filter(|p| is_partial_template(p)) {
        let content = file_reader.read_to_string(templates_dir.join(partial))?;
        let partial = partial.with_extension("");

        // Unwrap is safe as the `is_partial_template` predicate expects a valid filename.
        let filename = util::filename_to_string(partial.file_name().unwrap())?;

        // `is_partial_template` guarantees this filename starts with a `_`.
        let partial_name = partial.with_file_name(&filename[1..]);

        handlebars.register_partial(&partial_name.display().to_string(), content)?;
    }
    Ok(())
}

/// The arguments passed in during template execution.
/// The fields defined here represent what variables can be present in template files.
/// Add a field here and populate it to make it accessible in a template.
///
/// NOTE: The fields are serialized to JSON when passed to templates. The serialization
/// process renames all fields to UPPERCASE.
#[derive(Debug, Serialize)]
#[serde(rename_all = "UPPERCASE")]
struct TemplateArgs {
    /// The current year, for use in copyright headers.
    /// Reference from a template with `{{COPYRIGHT_YEAR}}`.
    copyright_year: String,

    /// The project name, as given on the command line.
    /// Reference from a template with `{{PROJECT_NAME}}`.
    project_name: String,

    /// The path to the new project, relative to the FUCHSIA_DIR environment variable.
    /// Reference from a template with `{{PROJECT_PATH}}`.
    project_path: String,

    /// The project-type, as specified on the command line. E.g. 'component-default'.
    project_type: String,
}

impl TemplateArgs {
    /// Build TemplateArgs from the program args and environment.
    fn from_create_args(create_args: &CreateArgs) -> Result<Self, anyhow::Error> {
        let project_path = if let Some(override_project_path) = &create_args.override_project_path {
            override_project_path.join(&create_args.project_path.project_name)
        } else {
            let absolute_project_path = create_args.absolute_project_path()?;
            let fuchsia_root = util::get_fuchsia_root()?;
            absolute_project_path
                .strip_prefix(&fuchsia_root)
                .map_err(|_| {
                    anyhow!(
                        "current working directory ({:?}) must be a descendant of FUCHSIA_DIR ({:?})", &absolute_project_path,
                        &fuchsia_root
                    )
                })?
                .to_path_buf()
        };

        let copyright_year = if let Some(year) = &create_args.override_copyright_year {
            year.to_string()
        } else {
            Utc::now().year().to_string()
        };

        Ok(TemplateArgs {
            copyright_year,
            project_name: create_args.project_path.project_name.clone(),
            project_path: project_path
                .to_str()
                .ok_or_else(|| anyhow!("invalid path {:?}", &project_path))?
                .to_string(),
            project_type: create_args.project_template()?,
        })
    }
}

/// The in-memory filtered template file tree.
#[derive(Debug, PartialEq)]
enum TemplateTree {
    /// A file and its template contents.
    File { source: PathBuf, content: String },

    /// A directory and its entries.
    Dir(HashMap<String, Box<TemplateTree>>),
}

impl TemplateTree {
    /// Populate a TemplateTree from a set of template files, ignoring partial templates (template files
    /// whose names begin with `_`).
    fn from_file_list<FR>(
        template_dir: &Path,
        template_files: &Vec<PathBuf>,
        project_type: &str,
        file_reader: &FR,
    ) -> Result<Self, anyhow::Error>
    where
        FR: FileReader,
    {
        let template_files = template_files
            .into_iter()
            .filter(|p| !is_partial_template(p))
            .collect::<Vec<&PathBuf>>();
        if template_files.is_empty() {
            bail!("no templates found for project type \"{}\"", project_type);
        }
        let mut tree = TemplateTree::Dir(HashMap::new());
        for path in template_files {
            let content = file_reader.read_to_string(template_dir.join(path))?;

            // The original template source for error reporting.
            let source = Path::new("//tools/create/templates").join(path);

            // Strip the project prefix from the path, which we know is there.
            let path = path.strip_prefix(project_type).unwrap();

            // Strip the .tmpl* extension. This will uncover the intended extension.
            // Eg: foo.rs.tmpl-rust -> foo.rs
            let path = path.with_extension("");

            tree.insert(&path, source, content)?;
        }
        Ok(tree)
    }

    fn insert(
        &mut self,
        path: &Path,
        source: PathBuf,
        content: String,
    ) -> Result<(), anyhow::Error> {
        let subtree = match self {
            Self::Dir(ref mut subtree) => subtree,
            Self::File { .. } => bail!("cannot insert subtree into file"),
        };

        let mut path_iter = path.components();
        if let Some(Component::Normal(component)) = path_iter.next() {
            let name = util::filename_to_string(component)?;
            let rest = path_iter.as_path();
            if path_iter.next().is_some() {
                subtree
                    .entry(name)
                    .or_insert_with(|| Box::new(TemplateTree::Dir(HashMap::new())))
                    .insert(rest, source, content)?;
            } else {
                if subtree.insert(name, Box::new(TemplateTree::File { source, content })).is_some()
                {
                    bail!("duplicate paths");
                }
            }
            Ok(())
        } else {
            bail!("path must be relative and have no '..' or '.' components");
        }
    }

    /// Recursively renders this TemplateTree into a mirror type [`RenderedTree`],
    /// using `handlebars` as the template engine and `args` as the exported variables
    // accessible to the templates.
    fn render(
        &self,
        handlebars: &mut Handlebars<'_>,
        args: &TemplateArgs,
    ) -> Result<RenderedTree, handlebars::RenderError> {
        Ok(match self {
            Self::File { source, content } => {
                let template_name = source.display().to_string();
                handlebars.register_template_string(&template_name, &content)?;
                let args = TemplateArgsWithTemplatePath { args, template_path: &template_name };
                let result = RenderedTree::File(handlebars.render(&template_name, &args)?);
                handlebars.unregister_template(&template_name);
                result
            }
            Self::Dir(nested_templates) => {
                let mut rendered_subtree = HashMap::new();
                for (filename, template) in nested_templates {
                    rendered_subtree.insert(
                        handlebars.render_template(&filename, args)?,
                        Box::new(template.render(handlebars, args)?),
                    );
                }
                RenderedTree::Dir(rendered_subtree)
            }
        })
    }
}

#[derive(Serialize)]
#[serde(rename_all = "UPPERCASE")]
struct TemplateArgsWithTemplatePath<'a> {
    #[serde(flatten)]
    args: &'a TemplateArgs,
    template_path: &'a str,
}

/// An in-memory representation of a file tree, where the paths and contents have
/// all been executed and rendered into their final form.
/// This is the mirror of [`TemplateTree`].
#[derive(Debug, PartialEq)]
enum RenderedTree {
    /// A file and its contents.
    File(String),

    /// A directory and its entries.
    Dir(HashMap<String, Box<RenderedTree>>),
}

impl RenderedTree {
    /// Write the RenderedTree to the `dest` path.
    fn write(&self, dest: &Path) -> Result<(), anyhow::Error> {
        match self {
            Self::File(contents) => {
                fs::write(dest, &contents)
                    .with_context(|| format!("failed to write to {:?}", dest))?;
            }
            Self::Dir(tree) => {
                fs::create_dir(dest)
                    .with_context(|| format!("failed to create directory {:?}", dest))?;
                for (filename, subtree) in tree {
                    let dest = dest.join(filename);
                    subtree.write(&dest)?;
                }
            }
        }
        Ok(())
    }
}

/// Trait to enable testing of the template tree creation logic.
/// Allows mocking out reading from the file system.
trait FileReader {
    fn read_to_string(&self, p: impl AsRef<Path>) -> Result<String, anyhow::Error>;
}

/// Standard library filesystem implementation of FileReader.
struct StdFs;

impl FileReader for StdFs {
    fn read_to_string(&self, p: impl AsRef<Path>) -> Result<String, anyhow::Error> {
        let p = p.as_ref();
        fs::read_to_string(p).with_context(|| format!("failed to read from {:?}", p))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use assert_matches::assert_matches;
    use test_util::lock_test_environment;

    #[test]
    fn project_path_parsed() {
        // Create a test environment and lock it to prevent races between tests
        // that modify the environment.
        let test_env = lock_test_environment();

        // Create a dir structure like //foo, where FUCHSIA_DIR points to //.
        let foo_path = test_env.path().join("foo");
        std::fs::File::create(&foo_path).expect("failed to create foo dir");

        // Test GN absolute labels.
        assert_eq!(
            "//foo/bar".parse::<ProjectPath>().unwrap(),
            ProjectPath { project_parent: foo_path.clone(), project_name: "bar".to_string() }
        );
        assert_eq!(
            "//bar".parse::<ProjectPath>().unwrap(),
            ProjectPath {
                project_parent: test_env.path().to_path_buf(),
                project_name: "bar".to_string()
            }
        );

        // Test absolute paths.
        assert_eq!(
            foo_path.join("bar").display().to_string().parse::<ProjectPath>().unwrap(),
            ProjectPath { project_parent: foo_path.clone(), project_name: "bar".to_string() }
        );
        assert_eq!(
            test_env.path().join("bar").display().to_string().parse::<ProjectPath>().unwrap(),
            ProjectPath {
                project_parent: test_env.path().to_path_buf(),
                project_name: "bar".to_string()
            }
        );

        // Test relative paths.
        assert_eq!(
            "foo/bar".parse::<ProjectPath>().unwrap(),
            ProjectPath { project_parent: foo_path.clone(), project_name: "bar".to_string() }
        );
        assert_eq!(
            "bar".parse::<ProjectPath>().unwrap(),
            ProjectPath {
                project_parent: test_env.path().to_path_buf(),
                project_name: "bar".to_string()
            }
        );
    }

    #[test]
    fn project_name_is_valid() {
        // Create a test environment and lock it to prevent races between tests
        // that modify the environment.
        let _test_env = lock_test_environment();

        assert_matches!("foo_bar".parse::<ProjectPath>(), Err(_));
        assert_matches!("foo.bar".parse::<ProjectPath>(), Err(_));
        assert_matches!("1foo".parse::<ProjectPath>(), Err(_));
        assert_matches!("-foo".parse::<ProjectPath>(), Err(_));

        assert_matches!("foo-bar".parse::<ProjectPath>(), Ok(_));
        assert_matches!("foo1".parse::<ProjectPath>(), Ok(_));
    }

    #[test]
    fn language_display_can_be_parsed() {
        assert_matches!(Language::Rust.to_string().parse(), Ok(Language::Rust));
        assert_matches!(Language::Cpp.to_string().parse(), Ok(Language::Cpp));
    }

    #[test]
    fn render_templates() {
        let templates = TemplateTree::Dir({
            let mut entries = HashMap::new();
            entries.insert(
                "file.h".to_string(),
                Box::new(TemplateTree::File {
                    source: PathBuf::from("//file.h.tmpl-cpp"),
                    content: "class {{PROJECT_NAME}};".to_string(),
                }),
            );
            entries.insert(
                "{{PROJECT_NAME}}_nested".to_string(),
                Box::new(TemplateTree::Dir({
                    let mut entries = HashMap::new();
                    entries.insert(
                        "file.h".to_string(),
                        Box::new(TemplateTree::File{
                            source: PathBuf::from("//{{PROJECT_NAME}}_nested/file.h.tmpl-cpp"),
                            content: "#include \"{{PROJECT_PATH}}/file.h\"\n// `fx create {{PROJECT_TYPE}}`"
                                .to_string(),
                        }),
                    );
                    entries
                })),
            );
            entries
        });

        let mut handlebars = Handlebars::new();
        handlebars.set_strict_mode(true);
        let args = TemplateArgs {
            copyright_year: "2020".to_string(),
            project_name: "foo".to_string(),
            project_path: "bar/foo".to_string(),
            project_type: "component".to_string(),
        };

        let rendered =
            templates.render(&mut handlebars, &args).expect("failed to render templates");
        assert_eq!(
            rendered,
            RenderedTree::Dir({
                let mut entries = HashMap::new();
                entries.insert(
                    "file.h".to_string(),
                    Box::new(RenderedTree::File("class foo;".to_string())),
                );
                entries.insert(
                    "foo_nested".to_string(),
                    Box::new(RenderedTree::Dir({
                        let mut entries = HashMap::new();
                        entries.insert(
                            "file.h".to_string(),
                            Box::new(RenderedTree::File(
                                "#include \"bar/foo/file.h\"\n// `fx create component`".to_string(),
                            )),
                        );
                        entries
                    })),
                );
                entries
            })
        );
    }

    impl<'a> FileReader for HashMap<&'a Path, &'a str> {
        fn read_to_string(&self, path: impl AsRef<Path>) -> Result<String, anyhow::Error> {
            self.get(path.as_ref()).map(|c| c.to_string()).ok_or_else(|| {
                anyhow::Error::from(io::Error::new(io::ErrorKind::NotFound, "file not found"))
            })
        }
    }

    #[test]
    fn template_tree_from_file_list() {
        let mut files = HashMap::new();
        files.insert(
            Path::new("create-templates/component-default/main.cc.tmpl-cpp"),
            r#"{{PROJECT_NAME}}"#,
        );
        let tree = TemplateTree::from_file_list(
            Path::new("create-templates"),
            &vec![PathBuf::from("component-default/main.cc.tmpl-cpp")],
            "component-default",
            &files,
        )
        .expect("failed");
        assert_matches!(tree, TemplateTree::Dir(nested) if nested.contains_key("main.cc"));
    }

    #[test]
    fn test_find_template_files() {
        let mut files = HashMap::new();
        files.insert(
            Path::new("create-templates/templates.json"),
            r#"[
                "_partial.tmpl",
                "component-default/_partial.tmpl",
                "component-default/src/main.rs.tmpl-rust"
            ]"#,
        );
        files.insert(Path::new("create-templates/_partial.tmpl"), r#"root {{PROJECT_NAME}}"#);
        files.insert(
            Path::new("create-templates/component-default/_partial.tmpl"),
            r#"component {{PROJECT_NAME}}"#,
        );
        files.insert(
            Path::new("create-templates/component-default/src/main.rs.tmpl-rust"),
            r#"component {{PROJECT_NAME}}"#,
        );
        let mut files = find_template_files(
            Path::new("create-templates/templates.json"),
            "component-default",
            &Language::Rust,
            &files,
        )
        .expect("failed");

        files.sort();
        assert_eq!(
            &files,
            &[
                PathBuf::from("_partial.tmpl"),
                PathBuf::from("component-default/_partial.tmpl"),
                PathBuf::from("component-default/src/main.rs.tmpl-rust"),
            ],
        );
    }

    #[test]
    fn test_register_partial_templates() {
        let mut files = HashMap::new();
        files.insert(Path::new("create-templates/_partial.tmpl"), r#"root {{PROJECT_NAME}}"#);
        files.insert(
            Path::new("create-templates/component-default/_partial.tmpl"),
            r#"component {{PROJECT_NAME}}"#,
        );
        let file_list = vec![
            PathBuf::from("_partial.tmpl"),
            PathBuf::from("component-default/_partial.tmpl"),
            PathBuf::from("component-default/src/main.rs.tmpl-rust"),
        ];
        let mut handlebars = Handlebars::new();
        register_partial_templates(
            &mut handlebars,
            Path::new("create-templates"),
            &file_list,
            &files,
        )
        .expect("failed");
        let registered_templates = handlebars.get_templates();
        assert!(registered_templates.contains_key("partial"));
        assert!(registered_templates.contains_key("component-default/partial"));
        assert_eq!(registered_templates.len(), 2);

        let mut args = HashMap::new();
        args.insert("PROJECT_NAME", "foo");
        assert_eq!(
            handlebars.render_template("{{>partial}}", &args).expect("failed to render"),
            "root foo"
        );
        assert_eq!(
            handlebars
                .render_template("{{>component-default/partial}}", &args)
                .expect("failed to render"),
            "component foo"
        );
    }
}