rust-clippy/clippy_lints/src/option_if_let_else.rs

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use crate::utils;
use crate::utils::eager_or_lazy;
use crate::utils::sugg::Sugg;
use crate::utils::{is_type_diagnostic_item, paths, span_lint_and_sugg};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// **What it does:**
/// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
/// idiomatically done with `Option::map_or` (if the else bit is a pure
/// expression) or `Option::map_or_else` (if the else bit is an impure
/// expression).
///
/// **Why is this bad?**
/// Using the dedicated functions of the Option type is clearer and
/// more concise than an `if let` expression.
///
/// **Known problems:**
/// This lint uses a deliberately conservative metric for checking
/// if the inside of either body contains breaks or continues which will
/// cause it to not suggest a fix if either block contains a loop with
/// continues or breaks contained within the loop.
///
/// **Example:**
///
/// ```rust
/// # let optional: Option<u32> = Some(0);
/// # fn do_complicated_function() -> u32 { 5 };
/// let _ = if let Some(foo) = optional {
/// foo
/// } else {
/// 5
/// };
/// let _ = if let Some(foo) = optional {
/// foo
/// } else {
/// let y = do_complicated_function();
/// y*y
/// };
/// ```
///
/// should be
///
/// ```rust
/// # let optional: Option<u32> = Some(0);
/// # fn do_complicated_function() -> u32 { 5 };
/// let _ = optional.map_or(5, |foo| foo);
/// let _ = optional.map_or_else(||{
/// let y = do_complicated_function();
/// y*y
/// }, |foo| foo);
/// ```
pub OPTION_IF_LET_ELSE,
pedantic,
"reimplementation of Option::map_or"
}
declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
/// Returns true iff the given expression is the result of calling `Result::ok`
fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
if let ExprKind::MethodCall(ref path, _, &[ref receiver], _) = &expr.kind {
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path.ident.name.as_str() == "ok"
&& is_type_diagnostic_item(cx, &cx.typeck_results().expr_ty(&receiver), sym::result_type)
} else {
false
}
}
/// A struct containing information about occurrences of the
/// `if let Some(..) = .. else` construct that this lint detects.
struct OptionIfLetElseOccurence {
option: String,
method_sugg: String,
some_expr: String,
none_expr: String,
wrap_braces: bool,
}
/// Extracts the body of a given arm. If the arm contains only an expression,
/// then it returns the expression. Otherwise, it returns the entire block
fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
if let ExprKind::Block(
Block {
stmts: statements,
expr: Some(expr),
..
},
_,
) = &arm.body.kind
{
if let [] = statements {
Some(&expr)
} else {
Some(&arm.body)
}
} else {
None
}
}
/// If this is the else body of an if/else expression, then we need to wrap
/// it in curly braces. Otherwise, we don't.
fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
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let mut should_wrap = false;
if let Some(Expr {
kind:
ExprKind::Match(
_,
arms,
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MatchSource::IfLetDesugar {
contains_else_clause: true,
},
),
..
}) = parent.expr
{
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should_wrap = expr.hir_id == arms[1].body.hir_id;
} else if let Some(Expr {
kind: ExprKind::If(_, _, Some(else_clause)),
..
}) = parent.expr
{
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should_wrap = expr.hir_id == else_clause.hir_id;
}
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should_wrap
})
}
fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
format!(
"{}{}",
Sugg::hir(cx, cond_expr, "..").maybe_par(),
if as_mut {
".as_mut()"
} else if as_ref {
".as_ref()"
} else {
""
}
)
}
/// If this expression is the option if let/else construct we're detecting, then
/// this function returns an `OptionIfLetElseOccurence` struct with details if
/// this construct is found, or None if this construct is not found.
fn detect_option_if_let_else<'tcx>(
cx: &'_ LateContext<'tcx>,
expr: &'_ Expr<'tcx>,
) -> Option<OptionIfLetElseOccurence> {
if_chain! {
if !utils::in_macro(expr.span); // Don't lint macros, because it behaves weirdly
if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
if arms.len() == 2;
if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind;
if utils::match_qpath(struct_qpath, &paths::OPTION_SOME);
if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
if !utils::usage::contains_return_break_continue_macro(arms[0].body);
if !utils::usage::contains_return_break_continue_macro(arms[1].body);
then {
let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
let some_body = extract_body_from_arm(&arms[0])?;
let none_body = extract_body_from_arm(&arms[1])?;
let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" };
let capture_name = id.name.to_ident_string();
let wrap_braces = should_wrap_in_braces(cx, expr);
let (as_ref, as_mut) = match &cond_expr.kind {
ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
_ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
};
let cond_expr = match &cond_expr.kind {
// Pointer dereferencing happens automatically, so we can omit it in the suggestion
ExprKind::Unary(UnOp::UnDeref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
_ => cond_expr,
};
Some(OptionIfLetElseOccurence {
option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
method_sugg: method_sugg.to_string(),
some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
wrap_braces,
})
} else {
None
}
}
}
impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
if let Some(detection) = detect_option_if_let_else(cx, expr) {
span_lint_and_sugg(
cx,
OPTION_IF_LET_ELSE,
expr.span,
format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
"try",
format!(
"{}{}.{}({}, {}){}",
if detection.wrap_braces { "{ " } else { "" },
detection.option,
detection.method_sugg,
detection.none_expr,
detection.some_expr,
if detection.wrap_braces { " }" } else { "" },
),
Applicability::MaybeIncorrect,
);
}
}
}