src/tools/clippy/clippy_dev/src/new_lint.rs

use crate::clippy_project_root;
use std::fs::{self, OpenOptions};
use std::io::prelude::*;
use std::io::{self, ErrorKind};
use std::path::{Path, PathBuf};

struct LintData<'a> {
    pass: &'a str,
    name: &'a str,
    category: &'a str,
    project_root: PathBuf,
}

trait Context {
    fn context<C: AsRef<str>>(self, text: C) -> Self;
}

impl<T> Context for io::Result<T> {
    fn context<C: AsRef<str>>(self, text: C) -> Self {
        match self {
            Ok(t) => Ok(t),
            Err(e) => {
                let message = format!("{}: {}", text.as_ref(), e);
                Err(io::Error::new(ErrorKind::Other, message))
            },
        }
    }
}

/// Creates the files required to implement and test a new lint and runs `update_lints`.
///
/// # Errors
///
/// This function errors out if the files couldn't be created or written to.
pub fn create(pass: Option<&str>, lint_name: Option<&str>, category: Option<&str>) -> io::Result<()> {
    let lint = LintData {
        pass: pass.expect("`pass` argument is validated by clap"),
        name: lint_name.expect("`name` argument is validated by clap"),
        category: category.expect("`category` argument is validated by clap"),
        project_root: clippy_project_root(),
    };

    create_lint(&lint).context("Unable to create lint implementation")?;
    create_test(&lint).context("Unable to create a test for the new lint")
}

fn create_lint(lint: &LintData) -> io::Result<()> {
    let (pass_type, pass_lifetimes, pass_import, context_import) = match lint.pass {
        "early" => ("EarlyLintPass", "", "use rustc_ast::ast::*;", "EarlyContext"),
        "late" => ("LateLintPass", "<'_, '_>", "use rustc_hir::*;", "LateContext"),
        _ => {
            unreachable!("`pass_type` should only ever be `early` or `late`!");
        },
    };

    let camel_case_name = to_camel_case(lint.name);
    let lint_contents = get_lint_file_contents(
        pass_type,
        pass_lifetimes,
        lint.name,
        &camel_case_name,
        lint.category,
        pass_import,
        context_import,
    );

    let lint_path = format!("clippy_lints/src/{}.rs", lint.name);
    write_file(lint.project_root.join(&lint_path), lint_contents.as_bytes())
}

fn create_test(lint: &LintData) -> io::Result<()> {
    fn create_project_layout<P: Into<PathBuf>>(lint_name: &str, location: P, case: &str, hint: &str) -> io::Result<()> {
        let mut path = location.into().join(case);
        fs::create_dir(&path)?;
        write_file(path.join("Cargo.toml"), get_manifest_contents(lint_name, hint))?;

        path.push("src");
        fs::create_dir(&path)?;
        let header = format!("// compile-flags: --crate-name={}", lint_name);
        write_file(path.join("main.rs"), get_test_file_contents(lint_name, Some(&header)))?;

        Ok(())
    }

    if lint.category == "cargo" {
        let relative_test_dir = format!("tests/ui-cargo/{}", lint.name);
        let test_dir = lint.project_root.join(relative_test_dir);
        fs::create_dir(&test_dir)?;

        create_project_layout(lint.name, &test_dir, "fail", "Content that triggers the lint goes here")?;
        create_project_layout(lint.name, &test_dir, "pass", "This file should not trigger the lint")
    } else {
        let test_path = format!("tests/ui/{}.rs", lint.name);
        let test_contents = get_test_file_contents(lint.name, None);
        write_file(lint.project_root.join(test_path), test_contents)
    }
}

fn write_file<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> io::Result<()> {
    fn inner(path: &Path, contents: &[u8]) -> io::Result<()> {
        OpenOptions::new()
            .write(true)
            .create_new(true)
            .open(path)?
            .write_all(contents)
    }

    inner(path.as_ref(), contents.as_ref()).context(format!("writing to file: {}", path.as_ref().display()))
}

fn to_camel_case(name: &str) -> String {
    name.split('_')
        .map(|s| {
            if s.is_empty() {
                String::from("")
            } else {
                [&s[0..1].to_uppercase(), &s[1..]].concat()
            }
        })
        .collect()
}

fn get_test_file_contents(lint_name: &str, header_commands: Option<&str>) -> String {
    let mut contents = format!(
        "#![warn(clippy::{})]

fn main() {{
    // test code goes here
}}
",
        lint_name
    );

    if let Some(header) = header_commands {
        contents = format!("{}\n{}", header, contents);
    }

    contents
}

fn get_manifest_contents(lint_name: &str, hint: &str) -> String {
    format!(
        r#"
# {}

[package]
name = "{}"
version = "0.1.0"
publish = false

[workspace]
"#,
        hint, lint_name
    )
}

fn get_lint_file_contents(
    pass_type: &str,
    pass_lifetimes: &str,
    lint_name: &str,
    camel_case_name: &str,
    category: &str,
    pass_import: &str,
    context_import: &str,
) -> String {
    format!(
        "use rustc_lint::{{{type}, {context_import}}};
use rustc_session::{{declare_lint_pass, declare_tool_lint}};
{pass_import}

declare_clippy_lint! {{
    /// **What it does:**
    ///
    /// **Why is this bad?**
    ///
    /// **Known problems:** None.
    ///
    /// **Example:**
    ///
    /// ```rust
    /// // example code where clippy issues a warning
    /// ```
    /// Use instead:
    /// ```rust
    /// // example code which does not raise clippy warning
    /// ```
    pub {name_upper},
    {category},
    \"default lint description\"
}}

declare_lint_pass!({name_camel} => [{name_upper}]);

impl {type}{lifetimes} for {name_camel} {{}}
",
        type=pass_type,
        lifetimes=pass_lifetimes,
        name_upper=lint_name.to_uppercase(),
        name_camel=camel_case_name,
        category=category,
        pass_import=pass_import,
        context_import=context_import
    )
}

#[test]
fn test_camel_case() {
    let s = "a_lint";
    let s2 = to_camel_case(s);
    assert_eq!(s2, "ALint");

    let name = "a_really_long_new_lint";
    let name2 = to_camel_case(name);
    assert_eq!(name2, "AReallyLongNewLint");

    let name3 = "lint__name";
    let name4 = to_camel_case(name3);
    assert_eq!(name4, "LintName");
}