--- /dev/null
+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 {
+ 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| {
+ let mut should_wrap = false;
+
+ if let Some(Expr {
+ kind:
+ ExprKind::Match(
+ _,
+ arms,
+ MatchSource::IfLetDesugar {
+ contains_else_clause: true,
+ },
+ ),
+ ..
+ }) = parent.expr
+ {
+ should_wrap = expr.hir_id == arms[1].body.hir_id;
+ } else if let Some(Expr {
+ kind: ExprKind::If(_, _, Some(else_clause)),
+ ..
+ }) = parent.expr
+ {
+ should_wrap = expr.hir_id == else_clause.hir_id;
+ }
+
+ 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::Deref, 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,
+ );
+ }
+ }
+}
projects / rustc.git / blobdiff