318 lines
11 KiB
Rust
318 lines
11 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::sugg::Sugg;
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use clippy_utils::{
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can_move_expr_to_closure, eager_or_lazy, higher, in_constant, is_else_clause, is_res_lang_ctor, peel_blocks,
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peel_hir_expr_while, CaptureKind,
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};
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
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use rustc_hir::{Arm, BindingMode, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind, Path, QPath, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::declare_lint_pass;
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use rustc_span::SyntaxContext;
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declare_clippy_lint! {
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/// ### What it does
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/// Lints usage of `if let Some(v) = ... { y } else { x }` and
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/// `match .. { Some(v) => y, None/_ => x }` which are more
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/// idiomatically done with `Option::map_or` (if the else bit is a pure
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/// expression) or `Option::map_or_else` (if the else bit is an impure
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/// expression).
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///
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/// ### Why is this bad?
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/// Using the dedicated functions of the `Option` type is clearer and
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/// more concise than an `if let` expression.
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///
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/// ### Notes
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/// This lint uses a deliberately conservative metric for checking if the
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/// inside of either body contains loop control expressions `break` or
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/// `continue` (which cannot be used within closures). If these are found,
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/// this lint will not be raised.
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///
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/// ### Example
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/// ```no_run
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/// # let optional: Option<u32> = Some(0);
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/// # fn do_complicated_function() -> u32 { 5 };
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/// let _ = if let Some(foo) = optional {
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/// foo
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/// } else {
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/// 5
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/// };
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/// let _ = match optional {
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/// Some(val) => val + 1,
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/// None => 5
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/// };
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/// let _ = if let Some(foo) = optional {
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/// foo
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/// } else {
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/// let y = do_complicated_function();
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/// y*y
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/// };
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/// ```
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///
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/// should be
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///
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/// ```no_run
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/// # let optional: Option<u32> = Some(0);
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/// # fn do_complicated_function() -> u32 { 5 };
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/// let _ = optional.map_or(5, |foo| foo);
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/// let _ = optional.map_or(5, |val| val + 1);
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/// let _ = optional.map_or_else(||{
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/// let y = do_complicated_function();
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/// y*y
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/// }, |foo| foo);
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/// ```
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// FIXME: Before moving this lint out of nursery, the lint name needs to be updated. It now also
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// covers matches and `Result`.
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#[clippy::version = "1.47.0"]
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pub OPTION_IF_LET_ELSE,
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nursery,
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"reimplementation of Option::map_or"
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}
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declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
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/// A struct containing information about occurrences of construct that this lint detects
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///
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/// Such as:
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///
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/// ```ignore
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/// if let Some(..) = {..} else {..}
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/// ```
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/// or
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/// ```ignore
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/// match x {
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/// Some(..) => {..},
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/// None/_ => {..}
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/// }
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/// ```
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struct OptionOccurrence {
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option: String,
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method_sugg: String,
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some_expr: String,
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none_expr: String,
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}
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fn format_option_in_sugg(cond_sugg: Sugg<'_>, as_ref: bool, as_mut: bool) -> String {
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format!(
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"{}{}",
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cond_sugg.maybe_par(),
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if as_mut {
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".as_mut()"
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} else if as_ref {
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".as_ref()"
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} else {
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""
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}
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)
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}
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fn try_get_option_occurrence<'tcx>(
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cx: &LateContext<'tcx>,
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ctxt: SyntaxContext,
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pat: &Pat<'tcx>,
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expr: &Expr<'_>,
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if_then: &'tcx Expr<'_>,
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if_else: &'tcx Expr<'_>,
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) -> Option<OptionOccurrence> {
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let cond_expr = match expr.kind {
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ExprKind::Unary(UnOp::Deref, inner_expr) | ExprKind::AddrOf(_, _, inner_expr) => inner_expr,
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_ => expr,
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};
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let (inner_pat, is_result) = try_get_inner_pat_and_is_result(cx, pat)?;
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if let PatKind::Binding(bind_annotation, _, id, None) = inner_pat.kind
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&& let Some(some_captures) = can_move_expr_to_closure(cx, if_then)
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&& let Some(none_captures) = can_move_expr_to_closure(cx, if_else)
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&& some_captures
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.iter()
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.filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
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.all(|(x, y)| x.is_imm_ref() && y.is_imm_ref())
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{
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let capture_mut = if bind_annotation == BindingMode::MUT {
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"mut "
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} else {
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""
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};
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let some_body = peel_blocks(if_then);
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let none_body = peel_blocks(if_else);
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let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) {
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"map_or"
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} else {
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"map_or_else"
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};
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let capture_name = id.name.to_ident_string();
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let (as_ref, as_mut) = match &expr.kind {
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ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
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ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
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_ if let Some(mutb) = cx.typeck_results().expr_ty(expr).ref_mutability() => {
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(mutb == Mutability::Not, mutb == Mutability::Mut)
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},
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_ => (
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bind_annotation == BindingMode::REF,
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bind_annotation == BindingMode::REF_MUT,
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),
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};
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// Check if captures the closure will need conflict with borrows made in the scrutinee.
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// TODO: check all the references made in the scrutinee expression. This will require interacting
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// with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
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if as_ref || as_mut {
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let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
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ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
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_ => None,
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});
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if let ExprKind::Path(QPath::Resolved(
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None,
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Path {
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res: Res::Local(local_id),
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..
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},
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)) = e.kind
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{
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match some_captures.get(local_id).or_else(|| {
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(method_sugg == "map_or_else")
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.then_some(())
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.and_then(|()| none_captures.get(local_id))
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}) {
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Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
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Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
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Some(CaptureKind::Ref(Mutability::Not)) | None => (),
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}
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}
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}
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let mut app = Applicability::Unspecified;
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let (none_body, is_argless_call) = match none_body.kind {
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ExprKind::Call(call_expr, []) if !none_body.span.from_expansion() => (call_expr, true),
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_ => (none_body, false),
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};
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return Some(OptionOccurrence {
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option: format_option_in_sugg(
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Sugg::hir_with_context(cx, cond_expr, ctxt, "..", &mut app),
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as_ref,
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as_mut,
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),
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method_sugg: method_sugg.to_string(),
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some_expr: format!(
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"|{capture_mut}{capture_name}| {}",
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Sugg::hir_with_context(cx, some_body, ctxt, "..", &mut app),
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),
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none_expr: format!(
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"{}{}",
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if method_sugg == "map_or" || is_argless_call {
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""
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} else if is_result {
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"|_| "
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} else {
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"|| "
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},
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Sugg::hir_with_context(cx, none_body, ctxt, "..", &mut app),
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),
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});
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}
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None
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}
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fn try_get_inner_pat_and_is_result<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'tcx>) -> Option<(&'tcx Pat<'tcx>, bool)> {
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if let PatKind::TupleStruct(ref qpath, [inner_pat], ..) = pat.kind {
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let res = cx.qpath_res(qpath, pat.hir_id);
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if is_res_lang_ctor(cx, res, OptionSome) {
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return Some((inner_pat, false));
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} else if is_res_lang_ctor(cx, res, ResultOk) {
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return Some((inner_pat, true));
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}
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}
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None
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}
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/// If this expression is the option if let/else construct we're detecting, then
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/// this function returns an `OptionOccurrence` struct with details if
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/// this construct is found, or None if this construct is not found.
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fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurrence> {
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if let Some(higher::IfLet {
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let_pat,
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let_expr,
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if_then,
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if_else: Some(if_else),
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..
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}) = higher::IfLet::hir(cx, expr)
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&& !cx.typeck_results().expr_ty(expr).is_unit()
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&& !is_else_clause(cx.tcx, expr)
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{
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try_get_option_occurrence(cx, expr.span.ctxt(), let_pat, let_expr, if_then, if_else)
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} else {
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None
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}
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}
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fn detect_option_match<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurrence> {
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if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind
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&& !cx.typeck_results().expr_ty(expr).is_unit()
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&& let Some((let_pat, if_then, if_else)) = try_convert_match(cx, arms)
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{
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try_get_option_occurrence(cx, expr.span.ctxt(), let_pat, ex, if_then, if_else)
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} else {
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None
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}
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}
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fn try_convert_match<'tcx>(
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cx: &LateContext<'tcx>,
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arms: &[Arm<'tcx>],
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) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
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if let [first_arm, second_arm] = arms
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&& first_arm.guard.is_none()
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&& second_arm.guard.is_none()
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{
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return if is_none_or_err_arm(cx, second_arm) {
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Some((first_arm.pat, first_arm.body, second_arm.body))
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} else if is_none_or_err_arm(cx, first_arm) {
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Some((second_arm.pat, second_arm.body, first_arm.body))
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} else {
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None
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};
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}
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None
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}
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fn is_none_or_err_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
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match arm.pat.kind {
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PatKind::Path(ref qpath) => is_res_lang_ctor(cx, cx.qpath_res(qpath, arm.pat.hir_id), OptionNone),
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PatKind::TupleStruct(ref qpath, [first_pat], _) => {
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is_res_lang_ctor(cx, cx.qpath_res(qpath, arm.pat.hir_id), ResultErr)
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&& matches!(first_pat.kind, PatKind::Wild)
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},
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PatKind::Wild => true,
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_ => false,
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}
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}
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impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
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// Don't lint macros and constants
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if expr.span.from_expansion() || in_constant(cx, expr.hir_id) {
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return;
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}
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let detection = detect_option_if_let_else(cx, expr).or_else(|| detect_option_match(cx, expr));
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if let Some(det) = detection {
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span_lint_and_sugg(
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cx,
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OPTION_IF_LET_ELSE,
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expr.span,
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format!("use Option::{} instead of an if let/else", det.method_sugg),
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"try",
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format!(
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"{}.{}({}, {})",
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det.option, det.method_sugg, det.none_expr, det.some_expr
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),
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Applicability::MaybeIncorrect,
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);
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}
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}
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}
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