jinja-codegen

# Jinja Codegen Mechanics The `jinja-templates` rule states the invariant: all parameterized generated code goes through Minijinja templates, never raw `format!`/`push_str`/`write!` assembly. This skill covers the mechanics of doing that correctly. ## Which `template_env` to call There is no `crate::template_env` module. Each backend and generator owns its own `template_env.rs`: - `src/backends/<lang>/template_env.rs` — per-language backend templates - `src/codegen/template_env.rs`, `src/core/template_env.rs`, `src/docs/template_env.rs`, `src/readme/template_env.rs`, `src/scaffold/template_env.rs`, `src/e2e/template_env.rs` — shared/generator-specific templates Call the one local to the code you are generating from: ```rust out.push_str(&crate::backends::<lang>::template_env::render("block_name.jinja", minijinja::context! { key => value, })); ``` ## Registering a template Register in the backend's `template_env.rs` via `include_str!`: ```rust ("block_name.jinja", include_str!("templates/block_name.jinja")), ``` One template per logical unit (class header, method signature, enum variant, etc.) — do not create generic line/content passthrough templates to bypass the `jinja-templates` rule. ## Engine settings Set in each `make_env()`: `trim_blocks = true`, `lstrip_blocks = true`, `keep_trailing_newline = true`. ## Inline templates Allowed only for single-line fragments used inside a larger template or join operation. Inline renders must call `.trim_end()` or `.trim_end_matches('\n')` at the call site, because templates keep their trailing newline — omitting the trim doubles blank lines in the emitted output. ## What Rust prepares vs. what the template owns Rust prepares typed values, identifiers, escaped literals, symbol names, type names, file paths, enum/field metadata, booleans, comma-joined argument lists, and small expression fragments when they are not a logical emitted unit. Templates own generated-code structure, indentation, and multiline blocks. Static `push_str("literal\n")` with no interpolation is fine to leave as-is — no template needed for non-parameterized strings. ## Anti-patterns - `push_str(&format!(...))`, `write!`/`writeln!` for interpolated output, or multiline `format!(...)`/`format!(r#"..."#)` that emits target code. - `format!(...)` strings containing `\n` for generated code. - Catch-all passthrough templates (e.g. `formatted_line.jinja` receiving `content => format!(...)`) used to route around the templating requirement. - Calling `crate::template_env::render` — that module does not exist; use the local one.