Cancel lint for given binding if field assignment references it

Author: Henri Lunnikivi

clippy_lints/src/field_reassign_with_default.rs

@@ -1,4 +1,4 @@
-use crate::utils::{match_def_path, paths, qpath_res, snippet, span_lint_and_note};
+use crate::utils::{contains_name, match_def_path, paths, qpath_res, snippet, span_lint_and_note};
 use if_chain::if_chain;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::Res;
@@ -55,9 +55,10 @@ impl LateLintPass<'_> for FieldReassignWithDefault {
             }
 
             // find all "later statement"'s where the fields of the binding set as
-            // Default::default() get reassigned
+            // Default::default() get reassigned, unless the reassignment refers to the original binding
             let mut first_assign = None;
             let mut assigned_fields = FxHashMap::default();
+            let mut cancel_lint = false;
             for consecutive_statement in &block.stmts[stmt_idx + 1..] {
                 // interrupt if the statement is a let binding (`Local`) that shadows the original
                 // binding
@@ -68,6 +69,12 @@ impl LateLintPass<'_> for FieldReassignWithDefault {
                 else if let Some((field_ident, assign_rhs)) =
                     field_reassigned_by_stmt(consecutive_statement, binding_name)
                 {
+                    // interrupt and cancel lint if assign_rhs references the original binding
+                    if contains_name(binding_name, assign_rhs) {
+                        cancel_lint = true;
+                        break;
+                    }
+
                     // always re-insert set value, this way the latest value is stored for output snippet
                     assigned_fields.insert(field_ident.name, assign_rhs);
 
@@ -84,7 +91,7 @@ impl LateLintPass<'_> for FieldReassignWithDefault {
 
             // if there are incorrectly assigned fields, do a span_lint_and_note to suggest
             // construction using `Ty { fields, ..Default::default() }`
-            if !assigned_fields.is_empty() {
+            if !assigned_fields.is_empty() && !cancel_lint {
                 // take the original assignment as span
                 let stmt = &block.stmts[stmt_idx];
 

tests/ui/field_reassign_with_default.rs

@@ -81,4 +81,9 @@ fn main() {
     let mut a: A = Default::default();
     a.i = Default::default();
     a.j = 45;
+
+    // right, because an assignment refers to another field
+    let mut x = A::default();
+    x.i = 42;
+    x.j = 21 + x.i as i64;
 }