Auto merge of rust-lang#8400 - Jarcho:split_matches, r=Manishearth

Split matches

Part of rust-lang#6680

changelog: None

clippy_lints/src/matches/infalliable_detructuring_match.rs

@@ -0,0 +1,44 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{path_to_local_id, peel_blocks, strip_pat_refs};
+use rustc_errors::Applicability;
+use rustc_hir::{ExprKind, Local, MatchSource, PatKind, QPath};
+use rustc_lint::LateContext;
+
+use super::INFALLIBLE_DESTRUCTURING_MATCH;
+
+pub(crate) fn check(cx: &LateContext<'_>, local: &Local<'_>) -> bool {
+    if_chain! {
+        if !local.span.from_expansion();
+        if let Some(expr) = local.init;
+        if let ExprKind::Match(target, arms, MatchSource::Normal) = expr.kind;
+        if arms.len() == 1 && arms[0].guard.is_none();
+        if let PatKind::TupleStruct(
+            QPath::Resolved(None, variant_name), args, _) = arms[0].pat.kind;
+        if args.len() == 1;
+        if let PatKind::Binding(_, arg, ..) = strip_pat_refs(&args[0]).kind;
+        let body = peel_blocks(arms[0].body);
+        if path_to_local_id(body, arg);
+
+        then {
+            let mut applicability = Applicability::MachineApplicable;
+            span_lint_and_sugg(
+                cx,
+                INFALLIBLE_DESTRUCTURING_MATCH,
+                local.span,
+                "you seem to be trying to use `match` to destructure a single infallible pattern. \
+                Consider using `let`",
+                "try this",
+                format!(
+                    "let {}({}) = {};",
+                    snippet_with_applicability(cx, variant_name.span, "..", &mut applicability),
+                    snippet_with_applicability(cx, local.pat.span, "..", &mut applicability),
+                    snippet_with_applicability(cx, target.span, "..", &mut applicability),
+                ),
+                applicability,
+            );
+            return true;
+        }
+    }
+    false
+}

clippy_lints/src/matches/match_as_ref.rs

@@ -0,0 +1,85 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{is_lang_ctor, peel_blocks};
+use rustc_errors::Applicability;
+use rustc_hir::{Arm, BindingAnnotation, Expr, ExprKind, LangItem, PatKind, QPath};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+
+use super::MATCH_AS_REF;
+
+pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
+    if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
+        let arm_ref: Option<BindingAnnotation> = if is_none_arm(cx, &arms[0]) {
+            is_ref_some_arm(cx, &arms[1])
+        } else if is_none_arm(cx, &arms[1]) {
+            is_ref_some_arm(cx, &arms[0])
+        } else {
+            None
+        };
+        if let Some(rb) = arm_ref {
+            let suggestion = if rb == BindingAnnotation::Ref {
+                "as_ref"
+            } else {
+                "as_mut"
+            };
+
+            let output_ty = cx.typeck_results().expr_ty(expr);
+            let input_ty = cx.typeck_results().expr_ty(ex);
+
+            let cast = if_chain! {
+                if let ty::Adt(_, substs) = input_ty.kind();
+                let input_ty = substs.type_at(0);
+                if let ty::Adt(_, substs) = output_ty.kind();
+                let output_ty = substs.type_at(0);
+                if let ty::Ref(_, output_ty, _) = *output_ty.kind();
+                if input_ty != output_ty;
+                then {
+                    ".map(|x| x as _)"
+                } else {
+                    ""
+                }
+            };
+
+            let mut applicability = Applicability::MachineApplicable;
+            span_lint_and_sugg(
+                cx,
+                MATCH_AS_REF,
+                expr.span,
+                &format!("use `{}()` instead", suggestion),
+                "try this",
+                format!(
+                    "{}.{}(){}",
+                    snippet_with_applicability(cx, ex.span, "_", &mut applicability),
+                    suggestion,
+                    cast,
+                ),
+                applicability,
+            );
+        }
+    }
+}
+
+// Checks if arm has the form `None => None`
+fn is_none_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
+    matches!(arm.pat.kind, PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, LangItem::OptionNone))
+}
+
+// Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
+fn is_ref_some_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> Option<BindingAnnotation> {
+    if_chain! {
+        if let PatKind::TupleStruct(ref qpath, [first_pat, ..], _) = arm.pat.kind;
+        if is_lang_ctor(cx, qpath, LangItem::OptionSome);
+        if let PatKind::Binding(rb, .., ident, _) = first_pat.kind;
+        if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
+        if let ExprKind::Call(e, args) = peel_blocks(arm.body).kind;
+        if let ExprKind::Path(ref some_path) = e.kind;
+        if is_lang_ctor(cx, some_path, LangItem::OptionSome) && args.len() == 1;
+        if let ExprKind::Path(QPath::Resolved(_, path2)) = args[0].kind;
+        if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
+        then {
+            return Some(rb)
+        }
+    }
+    None
+}

clippy_lints/src/matches/match_bool.rs

@@ -0,0 +1,75 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::is_unit_expr;
+use clippy_utils::source::{expr_block, snippet};
+use clippy_utils::sugg::Sugg;
+use rustc_ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Arm, Expr, ExprKind, PatKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+
+use super::MATCH_BOOL;
+
+pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
+    // Type of expression is `bool`.
+    if *cx.typeck_results().expr_ty(ex).kind() == ty::Bool {
+        span_lint_and_then(
+            cx,
+            MATCH_BOOL,
+            expr.span,
+            "you seem to be trying to match on a boolean expression",
+            move |diag| {
+                if arms.len() == 2 {
+                    // no guards
+                    let exprs = if let PatKind::Lit(arm_bool) = arms[0].pat.kind {
+                        if let ExprKind::Lit(ref lit) = arm_bool.kind {
+                            match lit.node {
+                                LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
+                                LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
+                                _ => None,
+                            }
+                        } else {
+                            None
+                        }
+                    } else {
+                        None
+                    };
+
+                    if let Some((true_expr, false_expr)) = exprs {
+                        let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
+                            (false, false) => Some(format!(
+                                "if {} {} else {}",
+                                snippet(cx, ex.span, "b"),
+                                expr_block(cx, true_expr, None, "..", Some(expr.span)),
+                                expr_block(cx, false_expr, None, "..", Some(expr.span))
+                            )),
+                            (false, true) => Some(format!(
+                                "if {} {}",
+                                snippet(cx, ex.span, "b"),
+                                expr_block(cx, true_expr, None, "..", Some(expr.span))
+                            )),
+                            (true, false) => {
+                                let test = Sugg::hir(cx, ex, "..");
+                                Some(format!(
+                                    "if {} {}",
+                                    !test,
+                                    expr_block(cx, false_expr, None, "..", Some(expr.span))
+                                ))
+                            },
+                            (true, true) => None,
+                        };
+
+                        if let Some(sugg) = sugg {
+                            diag.span_suggestion(
+                                expr.span,
+                                "consider using an `if`/`else` expression",
+                                sugg,
+                                Applicability::HasPlaceholders,
+                            );
+                        }
+                    }
+                }
+            },
+        );
+    }
+}

clippy_lints/src/matches/match_like_matches.rs

@@ -0,0 +1,166 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{higher, is_wild};
+use rustc_ast::{Attribute, LitKind};
+use rustc_errors::Applicability;
+use rustc_hir::{BorrowKind, Expr, ExprKind, Guard, MatchSource, Pat};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+use rustc_span::source_map::Spanned;
+
+use super::MATCH_LIKE_MATCHES_MACRO;
+
+/// Lint a `match` or `if let .. { .. } else { .. }` expr that could be replaced by `matches!`
+pub(crate) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
+    if let Some(higher::IfLet {
+        let_pat,
+        let_expr,
+        if_then,
+        if_else: Some(if_else),
+    }) = higher::IfLet::hir(cx, expr)
+    {
+        return find_matches_sugg(
+            cx,
+            let_expr,
+            IntoIterator::into_iter([(&[][..], Some(let_pat), if_then, None), (&[][..], None, if_else, None)]),
+            expr,
+            true,
+        );
+    }
+
+    if let ExprKind::Match(scrut, arms, MatchSource::Normal) = expr.kind {
+        return find_matches_sugg(
+            cx,
+            scrut,
+            arms.iter().map(|arm| {
+                (
+                    cx.tcx.hir().attrs(arm.hir_id),
+                    Some(arm.pat),
+                    arm.body,
+                    arm.guard.as_ref(),
+                )
+            }),
+            expr,
+            false,
+        );
+    }
+
+    false
+}
+
+/// Lint a `match` or `if let` for replacement by `matches!`
+fn find_matches_sugg<'a, 'b, I>(
+    cx: &LateContext<'_>,
+    ex: &Expr<'_>,
+    mut iter: I,
+    expr: &Expr<'_>,
+    is_if_let: bool,
+) -> bool
+where
+    'b: 'a,
+    I: Clone
+        + DoubleEndedIterator
+        + ExactSizeIterator
+        + Iterator<
+            Item = (
+                &'a [Attribute],
+                Option<&'a Pat<'b>>,
+                &'a Expr<'b>,
+                Option<&'a Guard<'b>>,
+            ),
+        >,
+{
+    if_chain! {
+        if iter.len() >= 2;
+        if cx.typeck_results().expr_ty(expr).is_bool();
+        if let Some((_, last_pat_opt, last_expr, _)) = iter.next_back();
+        let iter_without_last = iter.clone();
+        if let Some((first_attrs, _, first_expr, first_guard)) = iter.next();
+        if let Some(b0) = find_bool_lit(&first_expr.kind, is_if_let);
+        if let Some(b1) = find_bool_lit(&last_expr.kind, is_if_let);
+        if b0 != b1;
+        if first_guard.is_none() || iter.len() == 0;
+        if first_attrs.is_empty();
+        if iter
+            .all(|arm| {
+                find_bool_lit(&arm.2.kind, is_if_let).map_or(false, |b| b == b0) && arm.3.is_none() && arm.0.is_empty()
+            });
+        then {
+            if let Some(last_pat) = last_pat_opt {
+                if !is_wild(last_pat) {
+                    return false;
+                }
+            }
+
+            // The suggestion may be incorrect, because some arms can have `cfg` attributes
+            // evaluated into `false` and so such arms will be stripped before.
+            let mut applicability = Applicability::MaybeIncorrect;
+            let pat = {
+                use itertools::Itertools as _;
+                iter_without_last
+                    .filter_map(|arm| {
+                        let pat_span = arm.1?.span;
+                        Some(snippet_with_applicability(cx, pat_span, "..", &mut applicability))
+                    })
+                    .join(" | ")
+            };
+            let pat_and_guard = if let Some(Guard::If(g)) = first_guard {
+                format!("{} if {}", pat, snippet_with_applicability(cx, g.span, "..", &mut applicability))
+            } else {
+                pat
+            };
+
+            // strip potential borrows (#6503), but only if the type is a reference
+            let mut ex_new = ex;
+            if let ExprKind::AddrOf(BorrowKind::Ref, .., ex_inner) = ex.kind {
+                if let ty::Ref(..) = cx.typeck_results().expr_ty(ex_inner).kind() {
+                    ex_new = ex_inner;
+                }
+            };
+            span_lint_and_sugg(
+                cx,
+                MATCH_LIKE_MATCHES_MACRO,
+                expr.span,
+                &format!("{} expression looks like `matches!` macro", if is_if_let { "if let .. else" } else { "match" }),
+                "try this",
+                format!(
+                    "{}matches!({}, {})",
+                    if b0 { "" } else { "!" },
+                    snippet_with_applicability(cx, ex_new.span, "..", &mut applicability),
+                    pat_and_guard,
+                ),
+                applicability,
+            );
+            true
+        } else {
+            false
+        }
+    }
+}
+
+/// Extract a `bool` or `{ bool }`
+fn find_bool_lit(ex: &ExprKind<'_>, is_if_let: bool) -> Option<bool> {
+    match ex {
+        ExprKind::Lit(Spanned {
+            node: LitKind::Bool(b), ..
+        }) => Some(*b),
+        ExprKind::Block(
+            rustc_hir::Block {
+                stmts: &[],
+                expr: Some(exp),
+                ..
+            },
+            _,
+        ) if is_if_let => {
+            if let ExprKind::Lit(Spanned {
+                node: LitKind::Bool(b), ..
+            }) = exp.kind
+            {
+                Some(b)
+            } else {
+                None
+            }
+        },
+        _ => None,
+    }
+}