Auto merge of #12610 - ARandomDev99:manual_unwrap_or_default-12564, r=dswij

[`manual_unwrap_or_default`]: Check for Default trait implementation in initial condition when linting and use `IfLetOrMatch`

Fixes #12564

changelog: Fix [`manual_unwrap_or_default`] false positive when initial `match`/`if let` condition doesn't implement `Default` but the return type does.

4 files changed, 62 insertions, 55 deletions

diff --git a/clippy_lints/src/manual_unwrap_or_default.rs b/clippy_lints/src/manual_unwrap_or_default.rs
index c562ceb5bce..84fb183e3f7 100644
--- a/clippy_lints/src/manual_unwrap_or_default.rs
+++ b/clippy_lints/src/manual_unwrap_or_default.rs
@@ -1,13 +1,14 @@
-use clippy_utils::sugg::Sugg;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::{Arm, Expr, ExprKind, HirId, LangItem, MatchSource, Pat, PatKind, QPath};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::ty::GenericArgKind;
 use rustc_session::declare_lint_pass;
 use rustc_span::sym;
 
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::source::snippet_opt;
+use clippy_utils::higher::IfLetOrMatch;
+use clippy_utils::sugg::Sugg;
 use clippy_utils::ty::implements_trait;
 use clippy_utils::{in_constant, is_default_equivalent, peel_blocks, span_contains_comment};
 
@@ -105,19 +106,39 @@ fn get_some_and_none_bodies<'tcx>(
     }
 }
 
-fn handle_match<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
-    let ExprKind::Match(match_expr, [arm1, arm2], MatchSource::Normal | MatchSource::ForLoopDesugar) = expr.kind else {
-        return false;
+#[allow(clippy::needless_pass_by_value)]
+fn handle<'tcx>(cx: &LateContext<'tcx>, if_let_or_match: IfLetOrMatch<'tcx>, expr: &'tcx Expr<'tcx>) {
+    // Get expr_name ("if let" or "match" depending on kind of expression),  the condition, the body for
+    // the some arm, the body for the none arm and the binding id of the some arm
+    let (expr_name, condition, body_some, body_none, binding_id) = match if_let_or_match {
+        IfLetOrMatch::Match(condition, [arm1, arm2], MatchSource::Normal | MatchSource::ForLoopDesugar)
+            // Make sure there are no guards to keep things simple
+            if arm1.guard.is_none()
+                && arm2.guard.is_none()
+                // Get the some and none bodies and the binding id of the some arm
+                && let Some(((body_some, binding_id), body_none)) = get_some_and_none_bodies(cx, arm1, arm2) =>
+        {
+            ("match", condition, body_some, body_none, binding_id)
+        },
+        IfLetOrMatch::IfLet(condition, pat, if_expr, Some(else_expr), _)
+            if let Some(binding_id) = get_some(cx, pat) =>
+        {
+            ("if let", condition, if_expr, else_expr, binding_id)
+        },
+        _ => {
+            // All other cases (match with number of arms != 2, if let without else, etc.)
+            return;
+        },
     };
-    // We don't want conditions on the arms to simplify things.
-    if arm1.guard.is_none()
-        && arm2.guard.is_none()
-        // We check that the returned type implements the `Default` trait.
-        && let match_ty = cx.typeck_results().expr_ty(expr)
-        && let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default)
-        && implements_trait(cx, match_ty, default_trait_id, &[])
-        // We now get the bodies for both the `Some` and `None` arms.
-        && let Some(((body_some, binding_id), body_none)) = get_some_and_none_bodies(cx, arm1, arm2)
+
+    // We check if the return type of the expression implements Default.
+    let expr_type = cx.typeck_results().expr_ty(expr);
+    if let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default)
+        && implements_trait(cx, expr_type, default_trait_id, &[])
+        // We check if the initial condition implements Default.
+        && let Some(condition_ty) = cx.typeck_results().expr_ty(condition).walk().nth(1)
+        && let GenericArgKind::Type(condition_ty) = condition_ty.unpack()
+        && implements_trait(cx, condition_ty, default_trait_id, &[])
         // We check that the `Some(x) => x` doesn't do anything apart "returning" the value in `Some`.
         && let ExprKind::Path(QPath::Resolved(_, path)) = peel_blocks(body_some).kind
         && let Res::Local(local_id) = path.res
@@ -125,8 +146,9 @@ fn handle_match<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
         // We now check the `None` arm is calling a method equivalent to `Default::default`.
         && let body_none = peel_blocks(body_none)
         && is_default_equivalent(cx, body_none)
-        && let Some(receiver) = Sugg::hir_opt(cx, match_expr).map(Sugg::maybe_par)
+        && let Some(receiver) = Sugg::hir_opt(cx, condition).map(Sugg::maybe_par)
     {
+        // Machine applicable only if there are no comments present
         let applicability = if span_contains_comment(cx.sess().source_map(), expr.span) {
             Applicability::MaybeIncorrect
         } else {
@@ -136,48 +158,12 @@ fn handle_match<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
             cx,
             MANUAL_UNWRAP_OR_DEFAULT,
             expr.span,
-            "match can be simplified with `.unwrap_or_default()`",
+            format!("{expr_name} can be simplified with `.unwrap_or_default()`"),
             "replace it with",
             format!("{receiver}.unwrap_or_default()"),
             applicability,
         );
     }
-    true
-}
-
-fn handle_if_let<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
-    if let ExprKind::If(cond, if_block, Some(else_expr)) = expr.kind
-        && let ExprKind::Let(let_) = cond.kind
-        && let ExprKind::Block(_, _) = else_expr.kind
-        // We check that the returned type implements the `Default` trait.
-        && let match_ty = cx.typeck_results().expr_ty(expr)
-        && let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default)
-        && implements_trait(cx, match_ty, default_trait_id, &[])
-        && let Some(binding_id) = get_some(cx, let_.pat)
-        // We check that the `Some(x) => x` doesn't do anything apart "returning" the value in `Some`.
-        && let ExprKind::Path(QPath::Resolved(_, path)) = peel_blocks(if_block).kind
-        && let Res::Local(local_id) = path.res
-        && local_id == binding_id
-        // We now check the `None` arm is calling a method equivalent to `Default::default`.
-        && let body_else = peel_blocks(else_expr)
-        && is_default_equivalent(cx, body_else)
-        && let Some(if_let_expr_snippet) = snippet_opt(cx, let_.init.span)
-    {
-        let applicability = if span_contains_comment(cx.sess().source_map(), expr.span) {
-            Applicability::MaybeIncorrect
-        } else {
-            Applicability::MachineApplicable
-        };
-        span_lint_and_sugg(
-            cx,
-            MANUAL_UNWRAP_OR_DEFAULT,
-            expr.span,
-            "if let can be simplified with `.unwrap_or_default()`",
-            "replace it with",
-            format!("{if_let_expr_snippet}.unwrap_or_default()"),
-            applicability,
-        );
-    }
 }
 
 impl<'tcx> LateLintPass<'tcx> for ManualUnwrapOrDefault {
@@ -185,8 +171,9 @@ impl<'tcx> LateLintPass<'tcx> for ManualUnwrapOrDefault {
         if expr.span.from_expansion() || in_constant(cx, expr.hir_id) {
             return;
         }
-        if !handle_match(cx, expr) {
-            handle_if_let(cx, expr);
+        // Call handle only if the expression is `if let` or `match`
+        if let Some(if_let_or_match) = IfLetOrMatch::parse(cx, expr) {
+            handle(cx, if_let_or_match, expr);
         }
     }
 }
diff --git a/tests/ui/manual_unwrap_or_default.fixed b/tests/ui/manual_unwrap_or_default.fixed
index a0b707628a8..d6e736ba9cc 100644
--- a/tests/ui/manual_unwrap_or_default.fixed
+++ b/tests/ui/manual_unwrap_or_default.fixed
@@ -16,6 +16,16 @@ fn main() {
 
     let x: Option<Vec<String>> = None;
     x.unwrap_or_default();
+
+    // Issue #12564
+    // No error as &Vec<_> doesn't implement std::default::Default
+    let mut map = std::collections::HashMap::from([(0, vec![0; 3]), (1, vec![1; 3]), (2, vec![2])]);
+    let x: &[_] = if let Some(x) = map.get(&0) { x } else { &[] };
+    // Same code as above written using match.
+    let x: &[_] = match map.get(&0) {
+        Some(x) => x,
+        None => &[],
+    };
 }
 
 // Issue #12531
diff --git a/tests/ui/manual_unwrap_or_default.rs b/tests/ui/manual_unwrap_or_default.rs
index 1d4cca12f6c..462d5d90ee7 100644
--- a/tests/ui/manual_unwrap_or_default.rs
+++ b/tests/ui/manual_unwrap_or_default.rs
@@ -37,6 +37,16 @@ fn main() {
     } else {
         Vec::default()
     };
+
+    // Issue #12564
+    // No error as &Vec<_> doesn't implement std::default::Default
+    let mut map = std::collections::HashMap::from([(0, vec![0; 3]), (1, vec![1; 3]), (2, vec![2])]);
+    let x: &[_] = if let Some(x) = map.get(&0) { x } else { &[] };
+    // Same code as above written using match.
+    let x: &[_] = match map.get(&0) {
+        Some(x) => x,
+        None => &[],
+    };
 }
 
 // Issue #12531
diff --git a/tests/ui/manual_unwrap_or_default.stderr b/tests/ui/manual_unwrap_or_default.stderr
index d89212e6045..3f1da444301 100644
--- a/tests/ui/manual_unwrap_or_default.stderr
+++ b/tests/ui/manual_unwrap_or_default.stderr
@@ -53,7 +53,7 @@ LL | |     };
    | |_____^ help: replace it with: `x.unwrap_or_default()`
 
 error: match can be simplified with `.unwrap_or_default()`
-  --> tests/ui/manual_unwrap_or_default.rs:46:20
+  --> tests/ui/manual_unwrap_or_default.rs:56:20
    |
 LL |           Some(_) => match *b {
    |  ____________________^