585 lines
20 KiB
Rust
585 lines
20 KiB
Rust
use rustc::hir::*;
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use rustc::lint::*;
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use rustc::middle::const_val::ConstVal;
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use rustc::ty;
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use rustc_const_eval::ConstContext;
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use rustc_const_math::ConstInt;
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use std::cmp::Ordering;
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use std::collections::Bound;
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use syntax::ast::LitKind;
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use syntax::codemap::Span;
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use utils::paths;
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use utils::{match_type, snippet, span_note_and_lint, span_lint_and_then, in_external_macro, expr_block, walk_ptrs_ty,
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is_expn_of, remove_blocks};
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use utils::sugg::Sugg;
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/// **What it does:** Checks for matches with a single arm where an `if let`
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/// will usually suffice.
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///
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/// **Why is this bad?** Just readability – `if let` nests less than a `match`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// match x {
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/// Some(ref foo) => bar(foo),
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/// _ => ()
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/// }
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/// ```
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declare_lint! {
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pub SINGLE_MATCH,
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Warn,
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"a match statement with a single nontrivial arm (i.e. where the other arm \
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is `_ => {}`) instead of `if let`"
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}
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/// **What it does:** Checks for matches with a two arms where an `if let` will
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/// usually suffice.
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///
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/// **Why is this bad?** Just readability – `if let` nests less than a `match`.
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///
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/// **Known problems:** Personal style preferences may differ.
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///
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/// **Example:**
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/// ```rust
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/// match x {
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/// Some(ref foo) => bar(foo),
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/// _ => bar(other_ref),
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/// }
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/// ```
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declare_lint! {
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pub SINGLE_MATCH_ELSE,
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Allow,
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"a match statement with a two arms where the second arm's pattern is a wildcard \
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instead of `if let`"
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}
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/// **What it does:** Checks for matches where all arms match a reference,
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/// suggesting to remove the reference and deref the matched expression
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/// instead. It also checks for `if let &foo = bar` blocks.
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///
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/// **Why is this bad?** It just makes the code less readable. That reference
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/// destructuring adds nothing to the code.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// match x {
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/// &A(ref y) => foo(y),
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/// &B => bar(),
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/// _ => frob(&x),
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/// }
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/// ```
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declare_lint! {
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pub MATCH_REF_PATS,
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Warn,
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"a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
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}
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/// **What it does:** Checks for matches where match expression is a `bool`. It
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/// suggests to replace the expression with an `if...else` block.
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///
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/// **Why is this bad?** It makes the code less readable.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let condition: bool = true;
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/// match condition {
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/// true => foo(),
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/// false => bar(),
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/// }
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/// ```
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declare_lint! {
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pub MATCH_BOOL,
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Warn,
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"a match on a boolean expression instead of an `if..else` block"
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}
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/// **What it does:** Checks for overlapping match arms.
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///
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/// **Why is this bad?** It is likely to be an error and if not, makes the code
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/// less obvious.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let x = 5;
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/// match x {
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/// 1 ... 10 => println!("1 ... 10"),
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/// 5 ... 15 => println!("5 ... 15"),
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/// _ => (),
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/// }
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/// ```
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declare_lint! {
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pub MATCH_OVERLAPPING_ARM,
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Warn,
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"a match with overlapping arms"
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}
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/// **What it does:** Checks for arm which matches all errors with `Err(_)`
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/// and take drastic actions like `panic!`.
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///
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/// **Why is this bad?** It is generally a bad practice, just like
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/// catching all exceptions in java with `catch(Exception)`
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let x : Result(i32, &str) = Ok(3);
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/// match x {
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/// Ok(_) => println!("ok"),
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/// Err(_) => panic!("err"),
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/// }
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/// ```
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declare_lint! {
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pub MATCH_WILD_ERR_ARM,
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Warn,
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"a match with `Err(_)` arm and take drastic actions"
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}
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#[allow(missing_copy_implementations)]
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pub struct MatchPass;
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impl LintPass for MatchPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(SINGLE_MATCH,
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MATCH_REF_PATS,
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MATCH_BOOL,
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SINGLE_MATCH_ELSE,
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MATCH_OVERLAPPING_ARM,
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MATCH_WILD_ERR_ARM)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if in_external_macro(cx, expr.span) {
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return;
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}
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if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
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check_single_match(cx, ex, arms, expr);
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check_match_bool(cx, ex, arms, expr);
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check_overlapping_arms(cx, ex, arms);
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check_wild_err_arm(cx, ex, arms);
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}
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if let ExprMatch(ref ex, ref arms, source) = expr.node {
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check_match_ref_pats(cx, ex, arms, source, expr);
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}
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}
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}
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#[cfg_attr(rustfmt, rustfmt_skip)]
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fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
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if arms.len() == 2 &&
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arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
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arms[1].pats.len() == 1 && arms[1].guard.is_none() {
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let els = remove_blocks(&arms[1].body);
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let els = if is_unit_expr(els) {
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None
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} else if let ExprBlock(_) = els.node {
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// matches with blocks that contain statements are prettier as `if let + else`
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Some(els)
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} else {
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// allow match arms with just expressions
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return;
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};
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let ty = cx.tables.expr_ty(ex);
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if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
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check_single_match_single_pattern(cx, ex, arms, expr, els);
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check_single_match_opt_like(cx, ex, arms, expr, ty, els);
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}
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}
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}
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fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
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if arms[1].pats[0].node == PatKind::Wild {
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report_single_match_single_pattern(cx, ex, arms, expr, els);
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}
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}
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fn report_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
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let lint = if els.is_some() {
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SINGLE_MATCH_ELSE
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} else {
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SINGLE_MATCH
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};
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let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
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span_lint_and_then(cx,
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lint,
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expr.span,
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"you seem to be trying to use match for destructuring a single pattern. Consider using `if \
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let`",
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|db| {
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db.span_suggestion(expr.span,
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"try this",
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format!("if let {} = {} {}{}",
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snippet(cx, arms[0].pats[0].span, ".."),
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snippet(cx, ex.span, ".."),
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expr_block(cx, &arms[0].body, None, ".."),
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els_str));
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});
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}
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fn check_single_match_opt_like(
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cx: &LateContext,
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ex: &Expr,
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arms: &[Arm],
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expr: &Expr,
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ty: ty::Ty,
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els: Option<&Expr>
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) {
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// list of candidate Enums we know will never get any more members
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let candidates = &[(&paths::COW, "Borrowed"),
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(&paths::COW, "Cow::Borrowed"),
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(&paths::COW, "Cow::Owned"),
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(&paths::COW, "Owned"),
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(&paths::OPTION, "None"),
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(&paths::RESULT, "Err"),
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(&paths::RESULT, "Ok")];
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let path = match arms[1].pats[0].node {
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PatKind::TupleStruct(ref path, ref inner, _) => {
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// contains any non wildcard patterns? e.g. Err(err)
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if inner.iter().any(|pat| pat.node != PatKind::Wild) {
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return;
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}
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print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
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},
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PatKind::Binding(BindByValue(MutImmutable), _, ident, None) => ident.node.to_string(),
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PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
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_ => return,
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};
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for &(ty_path, pat_path) in candidates {
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if path == *pat_path && match_type(cx, ty, ty_path) {
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report_single_match_single_pattern(cx, ex, arms, expr, els);
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}
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}
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}
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fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
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// type of expression == bool
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if cx.tables.expr_ty(ex).sty == ty::TyBool {
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span_lint_and_then(cx,
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MATCH_BOOL,
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expr.span,
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"you seem to be trying to match on a boolean expression",
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move |db| {
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if arms.len() == 2 && arms[0].pats.len() == 1 {
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// no guards
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let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
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if let ExprLit(ref lit) = arm_bool.node {
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match lit.node {
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LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
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LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
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_ => None,
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}
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} else {
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None
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}
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} else {
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None
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};
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if let Some((true_expr, false_expr)) = exprs {
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let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
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(false, false) => {
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Some(format!("if {} {} else {}",
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snippet(cx, ex.span, "b"),
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expr_block(cx, true_expr, None, ".."),
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expr_block(cx, false_expr, None, "..")))
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},
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(false, true) => {
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Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
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},
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(true, false) => {
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let test = Sugg::hir(cx, ex, "..");
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Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
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},
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(true, true) => None,
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};
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if let Some(sugg) = sugg {
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db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
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}
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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 check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
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if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
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let ranges = all_ranges(cx, arms);
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let type_ranges = type_ranges(&ranges);
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if !type_ranges.is_empty() {
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if let Some((start, end)) = overlapping(&type_ranges) {
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span_note_and_lint(cx,
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MATCH_OVERLAPPING_ARM,
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start.span,
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"some ranges overlap",
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end.span,
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"overlaps with this");
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}
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}
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}
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}
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fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
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let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
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if match_type(cx, ex_ty, &paths::RESULT) {
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for arm in arms {
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if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
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let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
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if_let_chain! {[
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path_str == "Err",
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inner.iter().any(|pat| pat.node == PatKind::Wild),
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let ExprBlock(ref block) = arm.body.node,
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is_panic_block(block)
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], {
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// `Err(_)` arm with `panic!` found
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span_note_and_lint(cx,
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MATCH_WILD_ERR_ARM,
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arm.pats[0].span,
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"Err(_) will match all errors, maybe not a good idea",
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arm.pats[0].span,
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"to remove this warning, match each error seperately \
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or use unreachable macro");
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}}
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}
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}
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}
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}
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// If the block contains only a `panic!` macro (as expression or statement)
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fn is_panic_block(block: &Block) -> bool {
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match (&block.expr, block.stmts.len(), block.stmts.first()) {
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(&Some(ref exp), 0, _) => {
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is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
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},
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(&None, 1, Some(stmt)) => {
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is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
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},
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_ => false,
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}
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}
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fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
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if has_only_ref_pats(arms) {
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if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
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span_lint_and_then(cx,
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MATCH_REF_PATS,
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expr.span,
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"you don't need to add `&` to both the expression and the patterns",
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|db| {
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let inner = Sugg::hir(cx, inner, "..");
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let template = match_template(expr.span, source, &inner);
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db.span_suggestion(expr.span, "try", template);
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});
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} else {
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span_lint_and_then(cx,
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MATCH_REF_PATS,
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expr.span,
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"you don't need to add `&` to all patterns",
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|db| {
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let ex = Sugg::hir(cx, ex, "..");
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let template = match_template(expr.span, source, &ex.deref());
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db.span_suggestion(expr.span,
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"instead of prefixing all patterns with `&`, you can dereference the expression",
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template);
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});
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}
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}
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}
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/// Get all arms that are unbounded `PatRange`s.
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fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &[Arm]) -> Vec<SpannedRange<ConstVal<'tcx>>> {
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let constcx = ConstContext::with_tables(cx.tcx, cx.tables);
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arms.iter()
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.flat_map(|arm| {
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if let Arm { ref pats, guard: None, .. } = *arm {
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pats.iter()
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} else {
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[].iter()
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}
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.filter_map(|pat| {
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if_let_chain! {[
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let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
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let Ok(lhs) = constcx.eval(lhs),
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let Ok(rhs) = constcx.eval(rhs)
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], {
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let rhs = match *range_end {
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RangeEnd::Included => Bound::Included(rhs),
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RangeEnd::Excluded => Bound::Excluded(rhs),
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};
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return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
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}}
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if_let_chain! {[
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let PatKind::Lit(ref value) = pat.node,
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let Ok(value) = constcx.eval(value)
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], {
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return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
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}}
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None
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})
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})
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.collect()
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}
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#[derive(Debug, Eq, PartialEq)]
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pub struct SpannedRange<T> {
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pub span: Span,
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pub node: (T, Bound<T>),
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}
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type TypedRanges = Vec<SpannedRange<ConstInt>>;
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/// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
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/// `Uint` and `Int` probably don't make sense.
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fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
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ranges.iter()
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.filter_map(|range| match range.node {
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(ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
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Some(SpannedRange {
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span: range.span,
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node: (start, Bound::Included(end)),
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})
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},
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(ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
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Some(SpannedRange {
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span: range.span,
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node: (start, Bound::Excluded(end)),
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})
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},
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(ConstVal::Integral(start), Bound::Unbounded) => {
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Some(SpannedRange {
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span: range.span,
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node: (start, Bound::Unbounded),
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})
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},
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_ => None,
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})
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.collect()
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}
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fn is_unit_expr(expr: &Expr) -> bool {
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match expr.node {
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ExprTup(ref v) if v.is_empty() => true,
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ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
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_ => false,
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}
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}
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fn has_only_ref_pats(arms: &[Arm]) -> bool {
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let mapped = arms.iter()
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.flat_map(|a| &a.pats)
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.map(|p| {
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match p.node {
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PatKind::Ref(..) => Some(true), // &-patterns
|
||
PatKind::Wild => Some(false), // an "anything" wildcard is also fine
|
||
_ => None, // any other pattern is not fine
|
||
}
|
||
})
|
||
.collect::<Option<Vec<bool>>>();
|
||
// look for Some(v) where there's at least one true element
|
||
mapped.map_or(false, |v| v.iter().any(|el| *el))
|
||
}
|
||
|
||
fn match_template(span: Span, source: MatchSource, expr: &Sugg) -> String {
|
||
match source {
|
||
MatchSource::Normal => format!("match {} {{ .. }}", expr),
|
||
MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
|
||
MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
|
||
MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
|
||
MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
|
||
}
|
||
}
|
||
|
||
pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
|
||
where T: Copy + Ord
|
||
{
|
||
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
|
||
enum Kind<'a, T: 'a> {
|
||
Start(T, &'a SpannedRange<T>),
|
||
End(Bound<T>, &'a SpannedRange<T>),
|
||
}
|
||
|
||
impl<'a, T: Copy> Kind<'a, T> {
|
||
fn range(&self) -> &'a SpannedRange<T> {
|
||
match *self {
|
||
Kind::Start(_, r) |
|
||
Kind::End(_, r) => r,
|
||
}
|
||
}
|
||
|
||
fn value(self) -> Bound<T> {
|
||
match self {
|
||
Kind::Start(t, _) => Bound::Included(t),
|
||
Kind::End(t, _) => t,
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
|
||
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
|
||
Some(self.cmp(other))
|
||
}
|
||
}
|
||
|
||
impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
|
||
fn cmp(&self, other: &Self) -> Ordering {
|
||
match (self.value(), other.value()) {
|
||
(Bound::Included(a), Bound::Included(b)) |
|
||
(Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
|
||
// Range patterns cannot be unbounded (yet)
|
||
(Bound::Unbounded, _) |
|
||
(_, Bound::Unbounded) => unimplemented!(),
|
||
(Bound::Included(a), Bound::Excluded(b)) => {
|
||
match a.cmp(&b) {
|
||
Ordering::Equal => Ordering::Greater,
|
||
other => other,
|
||
}
|
||
},
|
||
(Bound::Excluded(a), Bound::Included(b)) => {
|
||
match a.cmp(&b) {
|
||
Ordering::Equal => Ordering::Less,
|
||
other => other,
|
||
}
|
||
},
|
||
}
|
||
}
|
||
}
|
||
|
||
let mut values = Vec::with_capacity(2 * ranges.len());
|
||
|
||
for r in ranges {
|
||
values.push(Kind::Start(r.node.0, r));
|
||
values.push(Kind::End(r.node.1, r));
|
||
}
|
||
|
||
values.sort();
|
||
|
||
for (a, b) in values.iter().zip(values.iter().skip(1)) {
|
||
match (a, b) {
|
||
(&Kind::Start(_, ra), &Kind::End(_, rb)) => {
|
||
if ra.node != rb.node {
|
||
return Some((ra, rb));
|
||
}
|
||
},
|
||
(&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
|
||
_ => return Some((a.range(), b.range())),
|
||
}
|
||
}
|
||
|
||
None
|
||
}
|