rust-clippy/clippy_lints/src/manual_unwrap_or.rs

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use crate::consts::constant_simple;
use crate::utils;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{def, Arm, Expr, ExprKind, PatKind, QPath};
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use rustc_lint::LintContext;
use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:**
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/// Finds patterns that reimplement `Option::unwrap_or`.
///
/// **Why is this bad?**
/// Concise code helps focusing on behavior instead of boilerplate.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let foo: Option<i32> = None;
/// match foo {
/// Some(v) => v,
/// None => 1,
/// };
/// ```
///
/// Use instead:
/// ```rust
/// let foo: Option<i32> = None;
/// foo.unwrap_or(1);
/// ```
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pub MANUAL_UNWRAP_OR,
complexity,
"finds patterns that can be encoded more concisely with `Option::unwrap_or(_else)`"
}
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declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
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impl LateLintPass<'_> for ManualUnwrapOr {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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if in_external_macro(cx.sess(), expr.span) {
return;
}
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lint_option_unwrap_or_case(cx, expr);
}
}
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fn lint_option_unwrap_or_case<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
fn applicable_none_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
if_chain! {
if arms.len() == 2;
if arms.iter().all(|arm| arm.guard.is_none());
if let Some((idx, none_arm)) = arms.iter().enumerate().find(|(_, arm)|
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if let PatKind::Path(ref qpath) = arm.pat.kind {
utils::match_qpath(qpath, &utils::paths::OPTION_NONE)
} else {
false
}
);
let some_arm = &arms[1 - idx];
if let PatKind::TupleStruct(ref some_qpath, &[some_binding], _) = some_arm.pat.kind;
if utils::match_qpath(some_qpath, &utils::paths::OPTION_SOME);
if let PatKind::Binding(_, binding_hir_id, ..) = some_binding.kind;
if let ExprKind::Path(QPath::Resolved(_, body_path)) = some_arm.body.kind;
if let def::Res::Local(body_path_hir_id) = body_path.res;
if body_path_hir_id == binding_hir_id;
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if !utils::usage::contains_return_break_continue_macro(none_arm.body);
then {
Some(none_arm)
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} else {
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None
}
}
}
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if_chain! {
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if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
let ty = cx.typeck_results().expr_ty(scrutinee);
if utils::is_type_diagnostic_item(cx, ty, sym!(option_type));
if let Some(none_arm) = applicable_none_arm(match_arms);
if let Some(scrutinee_snippet) = utils::snippet_opt(cx, scrutinee.span);
if let Some(none_body_snippet) = utils::snippet_opt(cx, none_arm.body.span);
if let Some(indent) = utils::indent_of(cx, expr.span);
then {
let reindented_none_body =
utils::reindent_multiline(none_body_snippet.into(), true, Some(indent));
let eager_eval = constant_simple(cx, cx.typeck_results(), none_arm.body).is_some();
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let method = if eager_eval {
"unwrap_or"
} else {
"unwrap_or_else"
};
utils::span_lint_and_sugg(
cx,
MANUAL_UNWRAP_OR, expr.span,
&format!("this pattern reimplements `Option::{}`", &method),
"replace with",
format!(
"{}.{}({}{})",
scrutinee_snippet,
method,
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if eager_eval { "" } else { "|| " },
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reindented_none_body
),
Applicability::MachineApplicable,
);
}
}
}