enhance [ifs_same_cond] to lint same immutable method calls as well

Author: J-ZhengLi

clippy_lints/src/copies.rs

@@ -3,8 +3,8 @@ use clippy_utils::source::{first_line_of_span, indent_of, reindent_multiline, sn
 use clippy_utils::ty::needs_ordered_drop;
 use clippy_utils::visitors::for_each_expr;
 use clippy_utils::{
-    capture_local_usage, eq_expr_value, get_enclosing_block, hash_expr, hash_stmt, if_sequence, is_else_clause,
-    is_lint_allowed, path_to_local, search_same, ContainsName, HirEqInterExpr, SpanlessEq,
+    capture_local_usage, eq_expr_value, find_binding_init, get_enclosing_block, hash_expr, hash_stmt, if_sequence,
+    is_else_clause, is_lint_allowed, path_to_local, search_same, ContainsName, HirEqInterExpr, SpanlessEq,
 };
 use core::iter;
 use core::ops::ControlFlow;
@@ -549,7 +549,27 @@ fn check_for_warn_of_moved_symbol(cx: &LateContext<'_>, symbols: &[(HirId, Symbo
 
 /// Implementation of `IFS_SAME_COND`.
 fn lint_same_cond(cx: &LateContext<'_>, conds: &[&Expr<'_>]) {
-    for (i, j) in search_same(conds, |e| hash_expr(cx, e), |lhs, rhs| eq_expr_value(cx, lhs, rhs)) {
+    for (i, j) in search_same(
+        conds,
+        |e| hash_expr(cx, e),
+        |lhs, rhs| {
+            // If any side (ex. lhs) is a method call, and the caller is not mutable,
+            // then we can ignore side effects?
+            if let ExprKind::MethodCall(_, caller, _, _) = lhs.kind {
+                if path_to_local(caller)
+                    .and_then(|hir_id| find_binding_init(cx, hir_id))
+                    .is_some()
+                {
+                    // caller is not declared as mutable
+                    SpanlessEq::new(cx).eq_expr(lhs, rhs)
+                } else {
+                    false
+                }
+            } else {
+                eq_expr_value(cx, lhs, rhs)
+            }
+        },
+    ) {
         span_lint_and_note(
             cx,
             IFS_SAME_COND,

tests/ui/ifs_same_cond.rs

@@ -43,4 +43,14 @@ fn ifs_same_cond() {
     }
 }
 
+fn issue10272() {
+    let a = String::from("ha");
+    if a.contains("ah") {
+    } else if a.contains("ah") {
+        // Trigger this lint
+    } else if a.contains("ha") {
+    } else if a == "wow" {
+    }
+}
+
 fn main() {}

tests/ui/ifs_same_cond.stderr

@@ -35,5 +35,17 @@ note: same as this
 LL |     if 2 * a == 1 {
    |        ^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: this `if` has the same condition as a previous `if`
+  --> $DIR/ifs_same_cond.rs:49:15
+   |
+LL |     } else if a.contains("ah") {
+   |               ^^^^^^^^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond.rs:48:8
+   |
+LL |     if a.contains("ah") {
+   |        ^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors