Fix unwrap_or_else_default false positive

Author: smoelius

clippy_lints/src/methods/unwrap_or_else_default.rs

@@ -1,10 +1,8 @@
 //! Lint for `some_result_or_option.unwrap_or_else(Default::default)`
 
 use super::UNWRAP_OR_ELSE_DEFAULT;
-use clippy_utils::{
-    diagnostics::span_lint_and_sugg, is_default_equivalent_call, source::snippet_with_applicability,
-    ty::is_type_diagnostic_item,
-};
+use clippy_utils::ty::{expr_type_is_certain, is_type_diagnostic_item};
+use clippy_utils::{diagnostics::span_lint_and_sugg, is_default_equivalent_call, source::snippet_with_applicability};
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -17,6 +15,10 @@ pub(super) fn check<'tcx>(
     recv: &'tcx hir::Expr<'_>,
     u_arg: &'tcx hir::Expr<'_>,
 ) {
+    if !expr_type_is_certain(cx, recv) {
+        return;
+    }
+
     // something.unwrap_or_else(Default::default)
     // ^^^^^^^^^- recv          ^^^^^^^^^^^^^^^^- u_arg
     // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^- expr

clippy_utils/src/ty.rs

@@ -30,6 +30,9 @@ use std::iter;
 
 use crate::{match_def_path, path_res, paths};
 
+mod type_certainty;
+pub use type_certainty::expr_type_is_certain;
+
 /// Checks if the given type implements copy.
 pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
     ty.is_copy_modulo_regions(cx.tcx, cx.param_env)

clippy_utils/src/ty/type_certainty/certainty.rs

@@ -0,0 +1,134 @@
+use rustc_hir::def_id::DefId;
+use std::fmt::Debug;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Certainty {
+    /// Determining the type requires contextual information.
+    Uncertain,
+
+    /// The type can be determined purely from subexpressions. If the argument is `Some(..)`, the
+    /// specific `DefId` is known. Such arguments are needed to handle path segments whose `res` is
+    /// `Res::Err`.
+    Certain(Option<DefId>),
+
+    /// The heuristic believes that more than one `DefId` applies to a type---this is a bug.
+    Contradiction,
+}
+
+pub trait Meet {
+    fn meet(self, other: Self) -> Self;
+}
+
+pub trait TryJoin: Sized {
+    fn try_join(self, other: Self) -> Option<Self>;
+}
+
+impl Meet for Option<DefId> {
+    fn meet(self, other: Self) -> Self {
+        match (self, other) {
+            (None, _) | (_, None) => None,
+            (Some(lhs), Some(rhs)) => {
+                if lhs == rhs {
+                    Some(lhs)
+                } else {
+                    None
+                }
+            },
+        }
+    }
+}
+
+impl TryJoin for Option<DefId> {
+    fn try_join(self, other: Self) -> Option<Self> {
+        match (self, other) {
+            (Some(lhs), Some(rhs)) => {
+                if lhs == rhs {
+                    Some(Some(lhs))
+                } else {
+                    None
+                }
+            },
+            (Some(def_id), _) | (_, Some(def_id)) => Some(Some(def_id)),
+            (None, None) => Some(None),
+        }
+    }
+}
+
+impl Meet for Certainty {
+    fn meet(self, other: Self) -> Self {
+        match (self, other) {
+            (Certainty::Uncertain, _) | (_, Certainty::Uncertain) => Certainty::Uncertain,
+            (Certainty::Certain(lhs), Certainty::Certain(rhs)) => Certainty::Certain(lhs.meet(rhs)),
+            (Certainty::Certain(inner), _) | (_, Certainty::Certain(inner)) => Certainty::Certain(inner),
+            (Certainty::Contradiction, Certainty::Contradiction) => Certainty::Contradiction,
+        }
+    }
+}
+
+impl Certainty {
+    /// Join two `Certainty`s preserving their `DefId`s (if any). Generally speaking, this method
+    /// should be used only when `self` and `other` refer directly to types. Otherwise,
+    /// `join_clearing_def_ids` should be used.
+    pub fn join(self, other: Self) -> Self {
+        match (self, other) {
+            (Certainty::Contradiction, _) | (_, Certainty::Contradiction) => Certainty::Contradiction,
+
+            (Certainty::Certain(lhs), Certainty::Certain(rhs)) => {
+                if let Some(inner) = lhs.try_join(rhs) {
+                    Certainty::Certain(inner)
+                } else {
+                    debug_assert!(false, "Contradiction with {lhs:?} and {rhs:?}");
+                    Certainty::Contradiction
+                }
+            },
+
+            (Certainty::Certain(inner), _) | (_, Certainty::Certain(inner)) => Certainty::Certain(inner),
+
+            (Certainty::Uncertain, Certainty::Uncertain) => Certainty::Uncertain,
+        }
+    }
+
+    /// Join two `Certainty`s after clearing their `DefId`s. This method should be used when `self`
+    /// or `other` do not necessarily refer to types, e.g., when they are aggregations of other
+    /// `Certainty`s.
+    pub fn join_clearing_def_ids(self, other: Self) -> Self {
+        self.clear_def_id().join(other.clear_def_id())
+    }
+
+    pub fn clear_def_id(self) -> Certainty {
+        match self {
+            Certainty::Uncertain => Certainty::Uncertain,
+            Certainty::Certain(_) => Certainty::Certain(None),
+            Certainty::Contradiction => Certainty::Contradiction,
+        }
+    }
+
+    pub fn with_def_id(self, def_id: DefId) -> Certainty {
+        match self {
+            Certainty::Uncertain => Certainty::Uncertain,
+            Certainty::Certain(_) => Certainty::Certain(Some(def_id)),
+            Certainty::Contradiction => Certainty::Contradiction,
+        }
+    }
+
+    pub fn to_def_id(self) -> Option<DefId> {
+        match self {
+            Certainty::Certain(inner) => inner,
+            _ => None,
+        }
+    }
+
+    pub fn is_certain(self) -> bool {
+        matches!(self, Self::Certain(_))
+    }
+}
+
+/// Think: `iter.all(/* is certain */)`
+pub fn meet(iter: impl Iterator<Item = Certainty>) -> Certainty {
+    iter.fold(Certainty::Certain(None), Certainty::meet)
+}
+
+/// Think: `iter.any(/* is certain */)`
+pub fn join(iter: impl Iterator<Item = Certainty>) -> Certainty {
+    iter.fold(Certainty::Uncertain, Certainty::join)
+}