rust-lang / rust-lang/rust-clippy

Suggest `impl FromStr` instead of `TryFrom<&str>`

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A-lint
Dominant language
Rust
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Description

What it does

Looks for impl TryFrom<&str> and suggest impl FromStr instead

Advantage

When parsing a string, FromStr is the idiomatic trait to implement, but that may not be immediately obvious to a Rust novice.

From the docs of TryFrom:

(TryFrom) is useful when you are doing a type conversion that may trivially succeed but may also need special handling

Parsing is something else completely, and for that trait FromStr is to be used.

See also @kangalio's comment on the inverse issue.

Drawbacks

If there is a lifetime on the type, then FromStr won't work, and so we should not make the suggestion in that cade.

Example
impl TryFrom<&str> for MyType {
    type Error = MyError;
    fn try_from(value: &strr) -> Result<Self, Self::Error> {

Could be written as:

impl FromStr MyType {
    type Err = MyError;
    fn from_str(value: &strr) -> Result<Self, Self::Err> {

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reviewing the linked inverse issue #5588 and the existing Clippy lint patterns for trait suggestions. Define the lifetime exception and diagnostic wording from the examples, then add coverage showing the suggestion for TryFrom<&str> and no suggestion when the type has a lifetime.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
devtools
Issue type
Feature
Difficulty
3/5
Estimated time
1-2 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
54/100

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