Fix branches_sharing_code suggests misleadingly when in assignment (#15076)

The lint will note `the end suggestion probably needs some adjustments
to use the expression result correctly` when the expr's is not unit. So
I extend this note to also appear when the expr is in an assignment.

changelog: [`branches_sharing_code`] fix misleading suggestions when in
assignment

Author: Jarcho

clippy_lints/src/copies.rs

@@ -11,7 +11,7 @@ use clippy_utils::{
 use core::iter;
 use core::ops::ControlFlow;
 use rustc_errors::Applicability;
-use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, HirIdSet, Stmt, StmtKind, intravisit};
+use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, HirIdSet, LetStmt, Node, Stmt, StmtKind, intravisit};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::impl_lint_pass;
@@ -295,7 +295,7 @@ fn lint_branches_sharing_code<'tcx>(
                 sugg,
                 Applicability::Unspecified,
             );
-            if !cx.typeck_results().expr_ty(expr).is_unit() {
+            if is_expr_parent_assignment(cx, expr) || !cx.typeck_results().expr_ty(expr).is_unit() {
                 diag.note("the end suggestion probably needs some adjustments to use the expression result correctly");
             }
         }
@@ -660,3 +660,17 @@ fn lint_same_fns_in_if_cond(cx: &LateContext<'_>, conds: &[&Expr<'_>]) {
         );
     }
 }
+
+fn is_expr_parent_assignment(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    let parent = cx.tcx.parent_hir_node(expr.hir_id);
+    if let Node::LetStmt(LetStmt { init: Some(e), .. })
+    | Node::Expr(Expr {
+        kind: ExprKind::Assign(_, e, _),
+        ..
+    }) = parent
+    {
+        return e.hir_id == expr.hir_id;
+    }
+
+    false
+}

tests/ui/branches_sharing_code/shared_at_bottom.rs

@@ -276,3 +276,27 @@ mod issue14873 {
         }
     }
 }
+
+fn issue15004() {
+    let a = 12u32;
+    let b = 13u32;
+    let mut c = 8u32;
+
+    let mut result = if b > a {
+        c += 1;
+        0
+    } else {
+        c += 2;
+        0
+        //~^ branches_sharing_code
+    };
+
+    result = if b > a {
+        c += 1;
+        1
+    } else {
+        c += 2;
+        1
+        //~^ branches_sharing_code
+    };
+}

tests/ui/branches_sharing_code/shared_at_bottom.stderr

@@ -172,5 +172,35 @@ LL ~         }
 LL +         let y = 1;
    |
 
-error: aborting due to 10 previous errors
+error: all if blocks contain the same code at the end
+  --> tests/ui/branches_sharing_code/shared_at_bottom.rs:290:5
+   |
+LL | /         0
+LL | |
+LL | |     };
+   | |_____^
+   |
+   = note: the end suggestion probably needs some adjustments to use the expression result correctly
+help: consider moving these statements after the if
+   |
+LL ~     }
+LL ~     0;
+   |
+
+error: all if blocks contain the same code at the end
+  --> tests/ui/branches_sharing_code/shared_at_bottom.rs:299:5
+   |
+LL | /         1
+LL | |
+LL | |     };
+   | |_____^
+   |
+   = note: the end suggestion probably needs some adjustments to use the expression result correctly
+help: consider moving these statements after the if
+   |
+LL ~     }
+LL ~     1;
+   |
+
+error: aborting due to 12 previous errors