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use rustc::lint::*;
use syntax::ast::*;
use syntax::codemap::Span;
use syntax::symbol::InternedString;
use utils::span_lint;

/// **What it does:** Checks for imports that remove "unsafe" from an item's
/// name.
///
/// **Why is this bad?** Renaming makes it less clear which traits and
/// structures are unsafe.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// use std::cell::{UnsafeCell as TotallySafeCell};
///
/// extern crate crossbeam;
/// use crossbeam::{spawn_unsafe as spawn};
/// ```
declare_clippy_lint! {
    pub UNSAFE_REMOVED_FROM_NAME,
    style,
    "`unsafe` removed from API names on import"
}

pub struct UnsafeNameRemoval;

impl LintPass for UnsafeNameRemoval {
    fn get_lints(&self) -> LintArray {
        lint_array!(UNSAFE_REMOVED_FROM_NAME)
    }
}

impl EarlyLintPass for UnsafeNameRemoval {
    fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
        if let ItemKind::Use(ref use_tree) = item.node {
            check_use_tree(use_tree, cx, &item.span);
        }
    }
}

fn check_use_tree(use_tree: &UseTree, cx: &EarlyContext, span: &Span) {
    match use_tree.kind {
        UseTreeKind::Simple(Some(new_name)) => {
            let old_name = use_tree
                .prefix
                .segments
                .last()
                .expect("use paths cannot be empty")
                .identifier;
            unsafe_to_safe_check(old_name, new_name, cx, span);
        }
        UseTreeKind::Simple(None) |
        UseTreeKind::Glob => {},
        UseTreeKind::Nested(ref nested_use_tree) => {
            for &(ref use_tree, _) in nested_use_tree {
                check_use_tree(use_tree, cx, span);
            }
        }
    }
}

fn unsafe_to_safe_check(old_name: Ident, new_name: Ident, cx: &EarlyContext, span: &Span) {
    let old_str = old_name.name.as_str();
    let new_str = new_name.name.as_str();
    if contains_unsafe(&old_str) && !contains_unsafe(&new_str) {
        span_lint(
            cx,
            UNSAFE_REMOVED_FROM_NAME,
            *span,
            &format!("removed \"unsafe\" from the name of `{}` in use as `{}`", old_str, new_str),
        );
    }
}

fn contains_unsafe(name: &InternedString) -> bool {
    name.contains("Unsafe") || name.contains("unsafe")
}