From 1303c76da43ae2c1798917a32c52df50275ca422 Mon Sep 17 00:00:00 2001
From: F3real <stefan92ff@yandex.com>
Date: Mon, 9 Aug 2021 09:49:55 +0200
Subject: [PATCH] Update suggestion in case function call is used in index

---
 clippy_lints/src/no_effect.rs         | 76 +++++++++++++++++++++------
 tests/ui/unnecessary_operation.fixed  |  4 +-
 tests/ui/unnecessary_operation.stderr |  4 +-
 3 files changed, 63 insertions(+), 21 deletions(-)

diff --git a/clippy_lints/src/no_effect.rs b/clippy_lints/src/no_effect.rs
index e07518b25868..b3bdef89a35c 100644
--- a/clippy_lints/src/no_effect.rs
+++ b/clippy_lints/src/no_effect.rs
@@ -94,33 +94,75 @@ impl<'tcx> LateLintPass<'tcx> for NoEffect {
             if has_no_effect(cx, expr) {
                 span_lint_hir(cx, NO_EFFECT, expr.hir_id, stmt.span, "statement with no effect");
             } else if let Some(reduced) = reduce_expression(cx, expr) {
-                let mut snippet = String::new();
-                for e in reduced {
+                for e in &reduced {
                     if e.span.from_expansion() {
                         return;
                     }
-                    if let Some(snip) = snippet_opt(cx, e.span) {
-                        snippet.push_str(&snip);
-                        snippet.push(';');
-                    } else {
-                        return;
+                }
+                if is_function_used_in_index(expr) {
+                    let snippet;
+                    if_chain! {
+                        if let Some(arr) = snippet_opt(cx, reduced[0].span);
+                        if let Some(func) = snippet_opt(cx, reduced[1].span);
+                        then {
+                            snippet = format!("assert!({}.len() > {});", &arr, &func);
+                        } else {
+                            return;
+                        }
                     }
+                    span_lint_hir_and_then(
+                        cx,
+                        UNNECESSARY_OPERATION,
+                        expr.hir_id,
+                        stmt.span,
+                        "statement can be reduced",
+                        |diag| {
+                            diag.span_suggestion(stmt.span, "replace it with", snippet, Applicability::MaybeIncorrect);
+                        },
+                    );
+                } else {
+                    let mut snippet = String::new();
+                    for e in reduced {
+                        if let Some(snip) = snippet_opt(cx, e.span) {
+                            snippet.push_str(&snip);
+                            snippet.push(';');
+                        } else {
+                            return;
+                        }
+                    }
+                    span_lint_hir_and_then(
+                        cx,
+                        UNNECESSARY_OPERATION,
+                        expr.hir_id,
+                        stmt.span,
+                        "statement can be reduced",
+                        |diag| {
+                            diag.span_suggestion(
+                                stmt.span,
+                                "replace it with",
+                                snippet,
+                                Applicability::MachineApplicable,
+                            );
+                        },
+                    );
                 }
-                span_lint_hir_and_then(
-                    cx,
-                    UNNECESSARY_OPERATION,
-                    expr.hir_id,
-                    stmt.span,
-                    "statement can be reduced",
-                    |diag| {
-                        diag.span_suggestion(stmt.span, "replace it with", snippet, Applicability::MachineApplicable);
-                    },
-                );
             }
         }
     }
 }
 
+fn is_function_used_in_index(expr: &Expr<'_>) -> bool {
+    if_chain! {
+        if let ExprKind::Index(_, b) = &expr.kind;
+        if let ExprKind::Call(..) | ExprKind::MethodCall(..) = &b.kind;
+        then {
+            true
+        } else {
+            false
+        }
+    }
+}
+
 fn reduce_expression<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<Vec<&'a Expr<'a>>> {
     if expr.span.from_expansion() {
         return None;
diff --git a/tests/ui/unnecessary_operation.fixed b/tests/ui/unnecessary_operation.fixed
index 2fca96c4cd55..bf0ec8deb345 100644
--- a/tests/ui/unnecessary_operation.fixed
+++ b/tests/ui/unnecessary_operation.fixed
@@ -62,10 +62,10 @@ fn main() {
     get_number();
     5;get_number();
     42;get_number();
-    [42, 55];get_usize();
+    assert!([42, 55].len() > get_usize());
     42;get_number();
     get_number();
-    [42; 55];get_usize();
+    assert!([42; 55].len() > get_usize());
     get_number();
     String::from("blah");
 
diff --git a/tests/ui/unnecessary_operation.stderr b/tests/ui/unnecessary_operation.stderr
index f88c9f9908be..a97bc167e2e7 100644
--- a/tests/ui/unnecessary_operation.stderr
+++ b/tests/ui/unnecessary_operation.stderr
@@ -88,7 +88,7 @@ error: statement can be reduced
   --> $DIR/unnecessary_operation.rs:65:5
    |
 LL |     [42, 55][get_usize()];
-   |     ^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `[42, 55];get_usize();`
+   |     ^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `assert!([42, 55].len() > get_usize());`
 
 error: statement can be reduced
   --> $DIR/unnecessary_operation.rs:66:5
@@ -106,7 +106,7 @@ error: statement can be reduced
   --> $DIR/unnecessary_operation.rs:68:5
    |
 LL |     [42; 55][get_usize()];
-   |     ^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `[42; 55];get_usize();`
+   |     ^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `assert!([42; 55].len() > get_usize());`
 
 error: statement can be reduced
   --> $DIR/unnecessary_operation.rs:69:5