Split out single_match

Author: Jarcho

clippy_lints/src/matches/mod.rs

@@ -3,15 +3,14 @@ use clippy_utils::diagnostics::{
     multispan_sugg, span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then,
 };
 use clippy_utils::macros::{is_panic, root_macro_call};
-use clippy_utils::paths;
 use clippy_utils::peel_blocks_with_stmt;
 use clippy_utils::source::{expr_block, indent_of, snippet, snippet_block, snippet_opt, snippet_with_applicability};
 use clippy_utils::sugg::Sugg;
-use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, match_type, peel_mid_ty_refs};
+use clippy_utils::ty::is_type_diagnostic_item;
 use clippy_utils::visitors::is_local_used;
 use clippy_utils::{
-    get_parent_expr, is_lang_ctor, is_lint_allowed, is_refutable, is_unit_expr, is_wild, meets_msrv, msrvs,
-    path_to_local_id, peel_blocks, peel_hir_pat_refs, peel_n_hir_expr_refs, recurse_or_patterns, strip_pat_refs,
+    get_parent_expr, is_lang_ctor, is_refutable, is_unit_expr, is_wild, meets_msrv, msrvs, path_to_local_id,
+    peel_blocks, peel_hir_pat_refs, recurse_or_patterns, strip_pat_refs,
 };
 use core::iter::once;
 use if_chain::if_chain;
@@ -20,19 +19,20 @@ use rustc_errors::Applicability;
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::LangItem::{OptionNone, OptionSome};
 use rustc_hir::{
-    self as hir, Arm, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, Local, MatchSource, Mutability, Node, Pat,
+    self as hir, Arm, BindingAnnotation, BorrowKind, Expr, ExprKind, Local, MatchSource, Mutability, Node, Pat,
     PatKind, PathSegment, QPath, RangeEnd, TyKind,
 };
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::{self, Ty, TyS, VariantDef};
+use rustc_middle::ty::{self, Ty, VariantDef};
 use rustc_semver::RustcVersion;
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{sym, symbol::kw, Span};
-use std::cmp::{max, Ordering};
+use std::cmp::Ordering;
 
 mod match_like_matches;
 mod match_same_arms;
 mod redundant_pattern_match;
+mod single_match;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -630,7 +630,7 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
         }
 
         if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind {
-            check_single_match(cx, ex, arms, expr);
+            single_match::check(cx, ex, arms, expr);
             check_match_bool(cx, ex, arms, expr);
             check_overlapping_arms(cx, ex, arms);
             check_wild_err_arm(cx, ex, arms);
@@ -710,262 +710,6 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
     extract_msrv_attr!(LateContext);
 }
 
-#[rustfmt::skip]
-fn check_single_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
-    if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
-        if expr.span.from_expansion() {
-            // Don't lint match expressions present in
-            // macro_rules! block
-            return;
-        }
-        if let PatKind::Or(..) = arms[0].pat.kind {
-            // don't lint for or patterns for now, this makes
-            // the lint noisy in unnecessary situations
-            return;
-        }
-        let els = arms[1].body;
-        let els = if is_unit_expr(peel_blocks(els)) {
-            None
-        } else if let ExprKind::Block(Block { stmts, expr: block_expr, .. }, _) = els.kind {
-            if stmts.len() == 1 && block_expr.is_none() || stmts.is_empty() && block_expr.is_some() {
-                // single statement/expr "else" block, don't lint
-                return;
-            }
-            // block with 2+ statements or 1 expr and 1+ statement
-            Some(els)
-        } else {
-            // not a block, don't lint
-            return;
-        };
-
-        let ty = cx.typeck_results().expr_ty(ex);
-        if *ty.kind() != ty::Bool || is_lint_allowed(cx, MATCH_BOOL, ex.hir_id) {
-            check_single_match_single_pattern(cx, ex, arms, expr, els);
-            check_single_match_opt_like(cx, ex, arms, expr, ty, els);
-        }
-    }
-}
-
-fn check_single_match_single_pattern(
-    cx: &LateContext<'_>,
-    ex: &Expr<'_>,
-    arms: &[Arm<'_>],
-    expr: &Expr<'_>,
-    els: Option<&Expr<'_>>,
-) {
-    if is_wild(arms[1].pat) {
-        report_single_match_single_pattern(cx, ex, arms, expr, els);
-    }
-}
-
-fn report_single_match_single_pattern(
-    cx: &LateContext<'_>,
-    ex: &Expr<'_>,
-    arms: &[Arm<'_>],
-    expr: &Expr<'_>,
-    els: Option<&Expr<'_>>,
-) {
-    let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
-    let els_str = els.map_or(String::new(), |els| {
-        format!(" else {}", expr_block(cx, els, None, "..", Some(expr.span)))
-    });
-
-    let (pat, pat_ref_count) = peel_hir_pat_refs(arms[0].pat);
-    let (msg, sugg) = if_chain! {
-        if let PatKind::Path(_) | PatKind::Lit(_) = pat.kind;
-        let (ty, ty_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(ex));
-        if let Some(spe_trait_id) = cx.tcx.lang_items().structural_peq_trait();
-        if let Some(pe_trait_id) = cx.tcx.lang_items().eq_trait();
-        if ty.is_integral() || ty.is_char() || ty.is_str()
-            || (implements_trait(cx, ty, spe_trait_id, &[])
-                && implements_trait(cx, ty, pe_trait_id, &[ty.into()]));
-        then {
-            // scrutinee derives PartialEq and the pattern is a constant.
-            let pat_ref_count = match pat.kind {
-                // string literals are already a reference.
-                PatKind::Lit(Expr { kind: ExprKind::Lit(lit), .. }) if lit.node.is_str() => pat_ref_count + 1,
-                _ => pat_ref_count,
-            };
-            // References are only implicitly added to the pattern, so no overflow here.
-            // e.g. will work: match &Some(_) { Some(_) => () }
-            // will not: match Some(_) { &Some(_) => () }
-            let ref_count_diff = ty_ref_count - pat_ref_count;
-
-            // Try to remove address of expressions first.
-            let (ex, removed) = peel_n_hir_expr_refs(ex, ref_count_diff);
-            let ref_count_diff = ref_count_diff - removed;
-
-            let msg = "you seem to be trying to use `match` for an equality check. Consider using `if`";
-            let sugg = format!(
-                "if {} == {}{} {}{}",
-                snippet(cx, ex.span, ".."),
-                // PartialEq for different reference counts may not exist.
-                "&".repeat(ref_count_diff),
-                snippet(cx, arms[0].pat.span, ".."),
-                expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
-                els_str,
-            );
-            (msg, sugg)
-        } else {
-            let msg = "you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`";
-            let sugg = format!(
-                "if let {} = {} {}{}",
-                snippet(cx, arms[0].pat.span, ".."),
-                snippet(cx, ex.span, ".."),
-                expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
-                els_str,
-            );
-            (msg, sugg)
-        }
-    };
-
-    span_lint_and_sugg(
-        cx,
-        lint,
-        expr.span,
-        msg,
-        "try this",
-        sugg,
-        Applicability::HasPlaceholders,
-    );
-}
-
-fn check_single_match_opt_like<'a>(
-    cx: &LateContext<'a>,
-    ex: &Expr<'_>,
-    arms: &[Arm<'_>],
-    expr: &Expr<'_>,
-    ty: Ty<'a>,
-    els: Option<&Expr<'_>>,
-) {
-    // list of candidate `Enum`s we know will never get any more members
-    let candidates = &[
-        (&paths::COW, "Borrowed"),
-        (&paths::COW, "Cow::Borrowed"),
-        (&paths::COW, "Cow::Owned"),
-        (&paths::COW, "Owned"),
-        (&paths::OPTION, "None"),
-        (&paths::RESULT, "Err"),
-        (&paths::RESULT, "Ok"),
-    ];
-
-    // We want to suggest to exclude an arm that contains only wildcards or forms the exhaustive
-    // match with the second branch, without enum variants in matches.
-    if !contains_only_wilds(arms[1].pat) && !form_exhaustive_matches(arms[0].pat, arms[1].pat) {
-        return;
-    }
-
-    let mut paths_and_types = Vec::new();
-    if !collect_pat_paths(&mut paths_and_types, cx, arms[1].pat, ty) {
-        return;
-    }
-
-    let in_candidate_enum = |path_info: &(String, &TyS<'_>)| -> bool {
-        let (path, ty) = path_info;
-        for &(ty_path, pat_path) in candidates {
-            if path == pat_path && match_type(cx, ty, ty_path) {
-                return true;
-            }
-        }
-        false
-    };
-    if paths_and_types.iter().all(in_candidate_enum) {
-        report_single_match_single_pattern(cx, ex, arms, expr, els);
-    }
-}
-
-/// Collects paths and their types from the given patterns. Returns true if the given pattern could
-/// be simplified, false otherwise.
-fn collect_pat_paths<'a>(acc: &mut Vec<(String, Ty<'a>)>, cx: &LateContext<'a>, pat: &Pat<'_>, ty: Ty<'a>) -> bool {
-    match pat.kind {
-        PatKind::Wild => true,
-        PatKind::Tuple(inner, _) => inner.iter().all(|p| {
-            let p_ty = cx.typeck_results().pat_ty(p);
-            collect_pat_paths(acc, cx, p, p_ty)
-        }),
-        PatKind::TupleStruct(ref path, ..) => {
-            let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
-                s.print_qpath(path, false);
-            });
-            acc.push((path, ty));
-            true
-        },
-        PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => {
-            acc.push((ident.to_string(), ty));
-            true
-        },
-        PatKind::Path(ref path) => {
-            let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
-                s.print_qpath(path, false);
-            });
-            acc.push((path, ty));
-            true
-        },
-        _ => false,
-    }
-}
-
-/// Returns true if the given arm of pattern matching contains wildcard patterns.
-fn contains_only_wilds(pat: &Pat<'_>) -> bool {
-    match pat.kind {
-        PatKind::Wild => true,
-        PatKind::Tuple(inner, _) | PatKind::TupleStruct(_, inner, ..) => inner.iter().all(contains_only_wilds),
-        _ => false,
-    }
-}
-
-/// Returns true if the given patterns forms only exhaustive matches that don't contain enum
-/// patterns without a wildcard.
-fn form_exhaustive_matches(left: &Pat<'_>, right: &Pat<'_>) -> bool {
-    match (&left.kind, &right.kind) {
-        (PatKind::Wild, _) | (_, PatKind::Wild) => true,
-        (PatKind::Tuple(left_in, left_pos), PatKind::Tuple(right_in, right_pos)) => {
-            // We don't actually know the position and the presence of the `..` (dotdot) operator
-            // in the arms, so we need to evaluate the correct offsets here in order to iterate in
-            // both arms at the same time.
-            let len = max(
-                left_in.len() + {
-                    if left_pos.is_some() { 1 } else { 0 }
-                },
-                right_in.len() + {
-                    if right_pos.is_some() { 1 } else { 0 }
-                },
-            );
-            let mut left_pos = left_pos.unwrap_or(usize::MAX);
-            let mut right_pos = right_pos.unwrap_or(usize::MAX);
-            let mut left_dot_space = 0;
-            let mut right_dot_space = 0;
-            for i in 0..len {
-                let mut found_dotdot = false;
-                if i == left_pos {
-                    left_dot_space += 1;
-                    if left_dot_space < len - left_in.len() {
-                        left_pos += 1;
-                    }
-                    found_dotdot = true;
-                }
-                if i == right_pos {
-                    right_dot_space += 1;
-                    if right_dot_space < len - right_in.len() {
-                        right_pos += 1;
-                    }
-                    found_dotdot = true;
-                }
-                if found_dotdot {
-                    continue;
-                }
-                if !contains_only_wilds(&left_in[i - left_dot_space])
-                    && !contains_only_wilds(&right_in[i - right_dot_space])
-                {
-                    return false;
-                }
-            }
-            true
-        },
-        _ => false,
-    }
-}
-
 fn check_match_bool(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
     // Type of expression is `bool`.
     if *cx.typeck_results().expr_ty(ex).kind() == ty::Bool {