Added restriction lint: pattern-type-mismatch

CHANGELOG.md

@@ -1588,6 +1588,7 @@ Released 2018-09-13
 [`panicking_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#panicking_unwrap
 [`partialeq_ne_impl`]: https://rust-lang.github.io/rust-clippy/master/index.html#partialeq_ne_impl
 [`path_buf_push_overwrite`]: https://rust-lang.github.io/rust-clippy/master/index.html#path_buf_push_overwrite
+[`pattern_type_mismatch`]: https://rust-lang.github.io/rust-clippy/master/index.html#pattern_type_mismatch
 [`possible_missing_comma`]: https://rust-lang.github.io/rust-clippy/master/index.html#possible_missing_comma
 [`precedence`]: https://rust-lang.github.io/rust-clippy/master/index.html#precedence
 [`print_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#print_literal

clippy_lints/src/lib.rs

@@ -268,6 +268,7 @@ mod overflow_check_conditional;
 mod panic_unimplemented;
 mod partialeq_ne_impl;
 mod path_buf_push_overwrite;
+mod pattern_type_mismatch;
 mod precedence;
 mod ptr;
 mod ptr_offset_with_cast;
@@ -741,6 +742,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &panic_unimplemented::UNREACHABLE,
         &partialeq_ne_impl::PARTIALEQ_NE_IMPL,
         &path_buf_push_overwrite::PATH_BUF_PUSH_OVERWRITE,
+        &pattern_type_mismatch::PATTERN_TYPE_MISMATCH,
         &precedence::PRECEDENCE,
         &ptr::CMP_NULL,
         &ptr::MUT_FROM_REF,
@@ -1064,6 +1066,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| box unnested_or_patterns::UnnestedOrPatterns);
     store.register_late_pass(|| box macro_use::MacroUseImports::default());
     store.register_late_pass(|| box map_identity::MapIdentity);
+    store.register_late_pass(|| box pattern_type_mismatch::PatternTypeMismatch);
 
     store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
         LintId::of(&arithmetic::FLOAT_ARITHMETIC),
@@ -1097,6 +1100,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&panic_unimplemented::TODO),
         LintId::of(&panic_unimplemented::UNIMPLEMENTED),
         LintId::of(&panic_unimplemented::UNREACHABLE),
+        LintId::of(&pattern_type_mismatch::PATTERN_TYPE_MISMATCH),
         LintId::of(&shadow::SHADOW_REUSE),
         LintId::of(&shadow::SHADOW_SAME),
         LintId::of(&strings::STRING_ADD),

clippy_lints/src/pattern_type_mismatch.rs

@@ -0,0 +1,311 @@
+use crate::utils::{last_path_segment, span_lint_and_help};
+use rustc_hir::{
+    intravisit, Body, Expr, ExprKind, FieldPat, FnDecl, HirId, LocalSource, MatchSource, Mutability, Pat, PatKind,
+    QPath, Stmt, StmtKind,
+};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::subst::SubstsRef;
+use rustc_middle::ty::{AdtDef, FieldDef, Ty, TyKind, VariantDef};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Span;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for patterns that aren't exact representations of the types
+    /// they are applied to.
+    ///
+    /// To satisfy this lint, you will have to adjust either the expression that is matched
+    /// against or the pattern itself, as well as the bindings that are introduced by the
+    /// adjusted patterns. For matching you will have to either dereference the expression
+    /// with the `*` operator, or amend the patterns to explicitly match against `&<pattern>`
+    /// or `&mut <pattern>` depending on the reference mutability. For the bindings you need
+    /// to use the inverse. You can leave them as plain bindings if you wish for the value
+    /// to be copied, but you must use `ref mut <variable>` or `ref <variable>` to construct
+    /// a reference into the matched structure.
+    ///
+    /// If you are looking for a way to learn about ownership semantics in more detail, it
+    /// is recommended to look at IDE options available to you to highlight types, lifetimes
+    /// and reference semantics in your code. The available tooling would expose these things
+    /// in a general way even outside of the various pattern matching mechanics. Of course
+    /// this lint can still be used to highlight areas of interest and ensure a good understanding
+    /// of ownership semantics.
+    ///
+    /// **Why is this bad?** It isn't bad in general. But in some contexts it can be desirable
+    /// because it increases ownership hints in the code, and will guard against some changes
+    /// in ownership.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// This example shows the basic adjustments necessary to satisfy the lint. Note how
+    /// the matched expression is explicitly dereferenced with `*` and the `inner` variable
+    /// is bound to a shared borrow via `ref inner`.
+    ///
+    /// ```rust,ignore
+    /// // Bad
+    /// let value = &Some(Box::new(23));
+    /// match value {
+    ///     Some(inner) => println!("{}", inner),
+    ///     None => println!("none"),
+    /// }
+    ///
+    /// // Good
+    /// let value = &Some(Box::new(23));
+    /// match *value {
+    ///     Some(ref inner) => println!("{}", inner),
+    ///     None => println!("none"),
+    /// }
+    /// ```
+    ///
+    /// The following example demonstrates one of the advantages of the more verbose style.
+    /// Note how the second version uses `ref mut a` to explicitly declare `a` a shared mutable
+    /// borrow, while `b` is simply taken by value. This ensures that the loop body cannot
+    /// accidentally modify the wrong part of the structure.
+    ///
+    /// ```rust,ignore
+    /// // Bad
+    /// let mut values = vec![(2, 3), (3, 4)];
+    /// for (a, b) in &mut values {
+    ///     *a += *b;
+    /// }
+    ///
+    /// // Good
+    /// let mut values = vec![(2, 3), (3, 4)];
+    /// for &mut (ref mut a, b) in &mut values {
+    ///     *a += b;
+    /// }
+    /// ```
+    pub PATTERN_TYPE_MISMATCH,
+    restriction,
+    "type of pattern does not match the expression type"
+}
+
+declare_lint_pass!(PatternTypeMismatch => [PATTERN_TYPE_MISMATCH]);
+
+impl<'tcx> LateLintPass<'tcx> for PatternTypeMismatch {
+    fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+        if let StmtKind::Local(ref local) = stmt.kind {
+            if let Some(init) = &local.init {
+                if let Some(init_ty) = cx.tables().node_type_opt(init.hir_id) {
+                    let pat = &local.pat;
+                    if in_external_macro(cx.sess(), pat.span) {
+                        return;
+                    }
+                    let deref_possible = match local.source {
+                        LocalSource::Normal => DerefPossible::Possible,
+                        _ => DerefPossible::Impossible,
+                    };
+                    apply_lint(cx, pat, init_ty, deref_possible);
+                }
+            }
+        }
+    }
+
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if let ExprKind::Match(ref expr, arms, source) = expr.kind {
+            match source {
+                MatchSource::Normal | MatchSource::IfLetDesugar { .. } | MatchSource::WhileLetDesugar => {
+                    if let Some(expr_ty) = cx.tables().node_type_opt(expr.hir_id) {
+                        'pattern_checks: for arm in arms {
+                            let pat = &arm.pat;
+                            if in_external_macro(cx.sess(), pat.span) {
+                                continue 'pattern_checks;
+                            }
+                            if apply_lint(cx, pat, expr_ty, DerefPossible::Possible) {
+                                break 'pattern_checks;
+                            }
+                        }
+                    }
+                },
+                _ => (),
+            }
+        }
+    }
+
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        _: intravisit::FnKind<'tcx>,
+        _: &'tcx FnDecl<'_>,
+        body: &'tcx Body<'_>,
+        _: Span,
+        hir_id: HirId,
+    ) {
+        if let Some(fn_sig) = cx.tables().liberated_fn_sigs().get(hir_id) {
+            for (param, ty) in body.params.iter().zip(fn_sig.inputs().iter()) {
+                apply_lint(cx, &param.pat, ty, DerefPossible::Impossible);
+            }
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum DerefPossible {
+    Possible,
+    Impossible,
+}
+
+fn apply_lint<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, expr_ty: Ty<'tcx>, deref_possible: DerefPossible) -> bool {
+    let maybe_mismatch = find_first_mismatch(cx, pat, expr_ty, Level::Top);
+    if let Some((span, mutability, level)) = maybe_mismatch {
+        span_lint_and_help(
+            cx,
+            PATTERN_TYPE_MISMATCH,
+            span,
+            "type of pattern does not match the expression type",
+            None,
+            &format!(
+                "{}explicitly match against a `{}` pattern and adjust the enclosed variable bindings",
+                match (deref_possible, level) {
+                    (DerefPossible::Possible, Level::Top) => "use `*` to dereference the match expression or ",
+                    _ => "",
+                },
+                match mutability {
+                    Mutability::Mut => "&mut _",
+                    Mutability::Not => "&_",
+                },
+            ),
+        );
+        true
+    } else {
+        false
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+enum Level {
+    Top,
+    Lower,
+}
+
+#[allow(rustc::usage_of_ty_tykind)]
+fn find_first_mismatch<'tcx>(
+    cx: &LateContext<'tcx>,
+    pat: &Pat<'_>,
+    ty: Ty<'tcx>,
+    level: Level,
+) -> Option<(Span, Mutability, Level)> {
+    if let PatKind::Ref(ref sub_pat, _) = pat.kind {
+        if let TyKind::Ref(_, sub_ty, _) = ty.kind {
+            return find_first_mismatch(cx, sub_pat, sub_ty, Level::Lower);
+        }
+    }
+
+    if let TyKind::Ref(_, _, mutability) = ty.kind {
+        if is_non_ref_pattern(&pat.kind) {
+            return Some((pat.span, mutability, level));
+        }
+    }
+
+    if let PatKind::Struct(ref qpath, ref field_pats, _) = pat.kind {
+        if let TyKind::Adt(ref adt_def, ref substs_ref) = ty.kind {
+            if let Some(variant) = get_variant(adt_def, qpath) {
+                let field_defs = &variant.fields;
+                return find_first_mismatch_in_struct(cx, field_pats, field_defs, substs_ref);
+            }
+        }
+    }
+
+    if let PatKind::TupleStruct(ref qpath, ref pats, _) = pat.kind {
+        if let TyKind::Adt(ref adt_def, ref substs_ref) = ty.kind {
+            if let Some(variant) = get_variant(adt_def, qpath) {
+                let field_defs = &variant.fields;
+                let ty_iter = field_defs.iter().map(|field_def| field_def.ty(cx.tcx, substs_ref));
+                return find_first_mismatch_in_tuple(cx, pats, ty_iter);
+            }
+        }
+    }
+
+    if let PatKind::Tuple(ref pats, _) = pat.kind {
+        if let TyKind::Tuple(..) = ty.kind {
+            return find_first_mismatch_in_tuple(cx, pats, ty.tuple_fields());
+        }
+    }
+
+    if let PatKind::Or(sub_pats) = pat.kind {
+        for pat in sub_pats {
+            let maybe_mismatch = find_first_mismatch(cx, pat, ty, level);
+            if let Some(mismatch) = maybe_mismatch {
+                return Some(mismatch);
+            }
+        }
+    }
+
+    None
+}
+
+fn get_variant<'a>(adt_def: &'a AdtDef, qpath: &QPath<'_>) -> Option<&'a VariantDef> {
+    if adt_def.is_struct() {
+        if let Some(variant) = adt_def.variants.iter().next() {
+            return Some(variant);
+        }
+    }
+
+    if adt_def.is_enum() {
+        let pat_ident = last_path_segment(qpath).ident;
+        for variant in &adt_def.variants {
+            if variant.ident == pat_ident {
+                return Some(variant);
+            }
+        }
+    }
+
+    None
+}
+
+fn find_first_mismatch_in_tuple<'tcx, I>(
+    cx: &LateContext<'tcx>,
+    pats: &[&Pat<'_>],
+    ty_iter_src: I,
+) -> Option<(Span, Mutability, Level)>
+where
+    I: IntoIterator<Item = Ty<'tcx>>,
+{
+    let mut field_tys = ty_iter_src.into_iter();
+    'fields: for pat in pats {
+        let field_ty = if let Some(ty) = field_tys.next() {
+            ty
+        } else {
+            break 'fields;
+        };
+
+        let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower);
+        if let Some(mismatch) = maybe_mismatch {
+            return Some(mismatch);
+        }
+    }
+
+    None
+}
+
+fn find_first_mismatch_in_struct<'tcx>(
+    cx: &LateContext<'tcx>,
+    field_pats: &[FieldPat<'_>],
+    field_defs: &[FieldDef],
+    substs_ref: SubstsRef<'tcx>,
+) -> Option<(Span, Mutability, Level)> {
+    for field_pat in field_pats {
+        'definitions: for field_def in field_defs {
+            if field_pat.ident == field_def.ident {
+                let field_ty = field_def.ty(cx.tcx, substs_ref);
+                let pat = &field_pat.pat;
+                let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower);
+                if let Some(mismatch) = maybe_mismatch {
+                    return Some(mismatch);
+                }
+                break 'definitions;
+            }
+        }
+    }
+
+    None
+}
+
+fn is_non_ref_pattern(pat_kind: &PatKind<'_>) -> bool {
+    match pat_kind {
+        PatKind::Struct(..) | PatKind::Tuple(..) | PatKind::TupleStruct(..) | PatKind::Path(..) => true,
+        PatKind::Or(sub_pats) => sub_pats.iter().any(|pat| is_non_ref_pattern(&pat.kind)),
+        _ => false,
+    }
+}

src/lintlist/mod.rs

@@ -1697,6 +1697,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
         deprecation: None,
         module: "path_buf_push_overwrite",
     },
+    Lint {
+        name: "pattern_type_mismatch",
+        group: "restriction",
+        desc: "type of pattern does not match the expression type",
+        deprecation: None,
+        module: "pattern_type_mismatch",
+    },
     Lint {
         name: "possible_missing_comma",
         group: "correctness",