268 lines
9.8 KiB
Rust
268 lines
9.8 KiB
Rust
use crate::utils;
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use crate::utils::sugg::Sugg;
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use crate::utils::{match_type, paths, span_lint_and_sugg};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
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use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::map::Map;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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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 }` which is more
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/// idiomatically done with `Option::map_or` (if the else bit is a simple
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/// expression) or `Option::map_or_else` (if the else bit is a longer
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/// block).
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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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/// **Known problems:**
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/// This lint uses whether the block is just an expression or if it has
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/// more statements to decide whether to use `Option::map_or` or
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/// `Option::map_or_else`. If you have a single expression which calls
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/// an expensive function, then it would be more efficient to use
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/// `Option::map_or_else`, but this lint would suggest `Option::map_or`.
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///
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/// Also, this lint uses a deliberately conservative metric for checking
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/// if the inside of either body contains breaks or continues which will
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/// cause it to not suggest a fix if either block contains a loop with
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/// continues or breaks contained within the loop.
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///
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/// **Example:**
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///
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/// ```rust
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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 _ = 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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/// ```rust
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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_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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pub OPTION_IF_LET_ELSE,
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pedantic,
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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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/// Returns true iff the given expression is the result of calling `Result::ok`
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fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
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if let ExprKind::MethodCall(ref path, _, &[ref receiver], _) = &expr.kind {
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path.ident.name.to_ident_string() == "ok"
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&& match_type(cx, &cx.typeck_results().expr_ty(&receiver), &paths::RESULT)
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} else {
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false
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}
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}
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/// A struct containing information about occurrences of the
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/// `if let Some(..) = .. else` construct that this lint detects.
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struct OptionIfLetElseOccurence {
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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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wrap_braces: bool,
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}
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struct ReturnBreakContinueMacroVisitor {
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seen_return_break_continue: bool,
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}
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impl ReturnBreakContinueMacroVisitor {
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fn new() -> ReturnBreakContinueMacroVisitor {
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ReturnBreakContinueMacroVisitor {
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seen_return_break_continue: false,
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}
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}
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}
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impl<'tcx> Visitor<'tcx> for ReturnBreakContinueMacroVisitor {
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type Map = Map<'tcx>;
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
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if self.seen_return_break_continue {
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// No need to look farther if we've already seen one of them
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return;
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}
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match &ex.kind {
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ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => {
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self.seen_return_break_continue = true;
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},
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// Something special could be done here to handle while or for loop
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// desugaring, as this will detect a break if there's a while loop
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// or a for loop inside the expression.
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_ => {
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if utils::in_macro(ex.span) {
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self.seen_return_break_continue = true;
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} else {
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rustc_hir::intravisit::walk_expr(self, ex);
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}
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},
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}
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}
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}
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fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool {
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let mut recursive_visitor = ReturnBreakContinueMacroVisitor::new();
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recursive_visitor.visit_expr(expression);
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recursive_visitor.seen_return_break_continue
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}
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/// Extracts the body of a given arm. If the arm contains only an expression,
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/// then it returns the expression. Otherwise, it returns the entire block
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fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
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if let ExprKind::Block(
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Block {
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stmts: statements,
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expr: Some(expr),
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..
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},
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_,
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) = &arm.body.kind
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{
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if let [] = statements {
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Some(&expr)
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} else {
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Some(&arm.body)
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}
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} else {
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None
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}
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}
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/// If this is the else body of an if/else expression, then we need to wrap
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/// it in curcly braces. Otherwise, we don't.
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fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
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if let Some(Expr {
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kind:
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ExprKind::Match(
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_,
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arms,
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MatchSource::IfDesugar {
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contains_else_clause: true,
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}
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| MatchSource::IfLetDesugar {
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contains_else_clause: true,
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},
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),
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..
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}) = parent.expr
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{
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expr.hir_id == arms[1].body.hir_id
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} else {
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false
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}
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})
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}
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fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
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format!(
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"{}{}",
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Sugg::hir(cx, cond_expr, "..").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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/// If this expression is the option if let/else construct we're detecting, then
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/// this function returns an `OptionIfLetElseOccurence` 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(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<OptionIfLetElseOccurence> {
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if_chain! {
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if !utils::in_macro(expr.span); // Don't lint macros, because it behaves weirdly
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if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
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if arms.len() == 2;
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if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
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if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind;
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if utils::match_qpath(struct_qpath, &paths::OPTION_SOME);
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if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
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if !contains_return_break_continue_macro(arms[0].body);
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if !contains_return_break_continue_macro(arms[1].body);
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then {
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let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
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let some_body = extract_body_from_arm(&arms[0])?;
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let none_body = extract_body_from_arm(&arms[1])?;
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let method_sugg = match &none_body.kind {
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ExprKind::Block(..) => "map_or_else",
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_ => "map_or",
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};
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let capture_name = id.name.to_ident_string();
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let wrap_braces = should_wrap_in_braces(cx, expr);
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let (as_ref, as_mut) = match &cond_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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_ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
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};
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let cond_expr = match &cond_expr.kind {
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// Pointer dereferencing happens automatically, so we can omit it in the suggestion
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ExprKind::Unary(UnOp::UnDeref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
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_ => cond_expr,
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};
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Some(OptionIfLetElseOccurence {
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option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
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method_sugg: method_sugg.to_string(),
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some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
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none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
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wrap_braces,
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})
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} else {
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None
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}
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}
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}
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impl<'a> LateLintPass<'a> for OptionIfLetElse {
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fn check_expr(&mut self, cx: &LateContext<'a>, expr: &Expr<'_>) {
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if let Some(detection) = detect_option_if_let_else(cx, expr) {
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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", detection.method_sugg).as_str(),
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"try",
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format!(
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"{}{}.{}({}, {}){}",
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if detection.wrap_braces { "{ " } else { "" },
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detection.option,
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detection.method_sugg,
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detection.none_expr,
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detection.some_expr,
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if detection.wrap_braces { " }" } else { "" },
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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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