Fixed issue #15192

Fixed issue #15192 by adding checks for no_std whild giving out Box recommendation

Author: lkshayb

clippy_lints/src/large_enum_variant.rs

@@ -8,6 +8,9 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{self, Ty};
 use rustc_session::impl_lint_pass;
 use rustc_span::Span;
+use clippy_utils::is_no_std_crate;
+
+
 
 declare_clippy_lint! {
     /// ### What it does
@@ -117,8 +120,9 @@ impl<'tcx> LateLintPass<'tcx> for LargeEnumVariant {
                                 ident.span,
                                 "boxing a variant would require the type no longer be `Copy`",
                             );
-                        } else {
-                            let sugg: Vec<(Span, String)> = variants_size[0]
+                        } else if !is_no_std_crate(cx) {
+                                
+                                let sugg: Vec<(Span, String)> = variants_size[0]
                                 .fields_size
                                 .iter()
                                 .rev()
@@ -144,12 +148,16 @@ impl<'tcx> LateLintPass<'tcx> for LargeEnumVariant {
                                 })
                                 .collect();
 
-                            if !sugg.is_empty() {
-                                diag.multipart_suggestion(help_text, sugg, Applicability::MaybeIncorrect);
-                                return;
+                                if !sugg.is_empty() {
+                                    diag.multipart_suggestion(help_text, sugg, Applicability::MaybeIncorrect);
+                                    return;
+                                }
                             }
+                            
+                        if !is_no_std_crate(cx) {
+                            diag.span_help(def.variants[variants_size[0].ind].span, help_text);
                         }
-                        diag.span_help(def.variants[variants_size[0].ind].span, help_text);
+                        
                     },
                 );
             }

tests/ui/large_enum_variant_no_std.rs

@@ -0,0 +1,15 @@
+#![no_std]
+#![no_main]
+#![warn(clippy::large_enum_variant)]
+
+use core::panic::PanicInfo;
+
+#[panic_handler]
+fn panic(_: &PanicInfo) -> ! {
+    loop {}
+}
+
+enum Myenum { //~ ERROR: large size difference between variants
+    Small(u8),
+    Large([u8;1024]),
+} 

tests/ui/large_enum_variant_no_std.stderr

@@ -0,0 +1,16 @@
+error: large size difference between variants
+  --> tests/ui/large_enum_variant_no_std.rs:12:1
+   |
+LL | / enum Myenum {
+LL | |     Small(u8),
+   | |     --------- the second-largest variant contains at least 1 bytes
+LL | |     Large([u8;1024]),
+   | |     ---------------- the largest variant contains at least 1024 bytes
+LL | | } 
+   | |_^ the entire enum is at least 1025 bytes
+   |
+   = note: `-D clippy::large-enum-variant` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::large_enum_variant)]`
+
+error: aborting due to 1 previous error
+