docstring-generator

name	docstring-generator
description	> Use when this capability is needed.

Docstring Generator

Generates or updates doc comments for TypeScript and Rust source files. The skill analyzes the public API surface (functions, methods, classes/structs, traits/interfaces, enums) and produces language-idiomatic documentation.

Inputs

Input	Type	Required	Description
language	string	yes	"typescript" or "rust"
file_path	string	yes	Path of the file being edited
full_text	string	yes	Entire contents of the file
selection_range	object	no	{ start_line, end_line } (1-based, inclusive)
mode	string	no	"update_missing" (default) or "update_all"
public_only	boolean	no	If true (default), only document exported/public items

Workflow

Step 1: Parse declarations

Mentally parse full_text to find all declarations relevant to the language, public_only, and selection_range settings.

TypeScript declarations to document:

• Exported functions, async functions, and generators
• Exported classes and their public/protected methods
• Exported interfaces and type aliases
• Exported enums
• Exported const/let/var at module level (when they hold complex types)

Rust declarations to document:

• pub fn (free functions and methods)
• pub struct and its pub fields
• pub enum and its variants
• pub trait and its method signatures
• pub type and pub const items
• pub mod (public modules)

Step 2: Generate doc comments

For each target declaration, follow the language-specific rules below.

Step 3: Merge into file

Insert or update the doc comment immediately before the declaration, preserving all existing formatting, indentation, and code. Return the full updated_text with only doc comment lines changed.

Behavior & Style Rules

General Rules (all languages)

• Preserve everything: Do not change code semantics, identifiers, formatting, or indentation. Only touch doc comment lines.
• No speculation: If unsure about behavior, write neutral high-level descriptions instead of guessing.
• Present tense, concise: Describe what the item does, not what it is. Avoid restating obvious type information unless it aids clarity.
• Idempotent: Running the skill twice on the same file should produce the same result.
• Respect developer notes: In update_all mode, preserve explicit warnings, safety notes, panic documentation, and custom annotations.

TypeScript Rules

Comment style: Use /** ... */ TSDoc/JSDoc block comments immediately before the declaration.

Functions & methods:

• First line: one-sentence summary of what the function does.
• Then @param name - description for each parameter.
• Then @returns with a short description if the function returns non-void.

Classes, interfaces, type aliases, enums:

• Summarize the purpose and role of the type.
• Prefer describing intent over implementation details.

Mode behavior:

• update_missing: Do not rewrite existing comments unless they are obviously placeholder (e.g., TODO, fix, FIXME, @todo).
• update_all: Improve unclear comments but preserve any explicit developer notes or warnings.

Example:

/** Loads a user by id from the primary data store.
 * @param id - Unique identifier of the user.
 * @returns The user if found, otherwise null.
 */
async function getUserById(id: string): Promise<User | null> {
  // ...
}

Overloaded/union-heavy functions: Describe the general behavior rather than each possible overload or union variant.

Rust Rules

Comment style: Use /// triple-slash line comments for item docs. Keep lines around 80 characters.

Structure:

• First line: brief summary sentence.
• Blank /// line, then details or examples as needed.
• For fallible functions, add a # Errors section if the error conditions are clear from the signature.
• Refer to types with backticks: `SomeType`.

Scope: Only document public API by default (pub fn, pub struct, pub enum, pub trait, pub methods on pub types).

Mode behavior:

• update_missing: Only add docs to items without existing /// comments.
• update_all: Refine awkward wording but preserve explicit notes like # Panics or # Safety.

Example:

/// Calculates the checksum for the given buffer.
///
/// # Errors
///
/// Returns an error if the buffer length exceeds the supported maximum.
pub fn checksum(buf: &[u8]) -> Result<u32, ChecksumError> {
    // ...
}

Selection Behavior

• If selection_range is provided: Only consider declarations that start within the selected line range. Do not modify docs for items outside the selection.
• If a declaration spans multiple lines and the selection includes its start line, treat the entire declaration as in-scope.
• If selection_range is omitted: Apply the chosen mode to the entire file, respecting public_only.

Edge Cases

• Generic names: If a symbol name is extremely generic (e.g., doStuff, handle), use surrounding code and types to infer a better description, but stay conservative.
• Insufficient context: If there isn't enough information to write a meaningful description, use a neutral description like "Performs the operation for this type" rather than fabricating details.
• Rust generics: Do not over-specify type parameters. Describe the concept and constraints at a high level.
• Selection mid-declaration: If the selection start line falls inside a multi-line declaration, still treat the entire declaration as in scope.

Output

Return these three values:

Field	Type	Description
updated_text	string	Full file text with updated doc comments
summary	string	1-3 sentence summary of what was documented
touched_symbols	string[]	Names of functions/types that had docs added or updated

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Source: espennilsen/pi — distributed by TomeVault.