Auto merge of #12149 - GuillaumeGomez:core-std-suggestions, r=llogiq

Correctly suggest std or core path depending if this is a `no_std` crate

A few lints emit suggestions using `std` paths whether or not this is a `no_std` crate, which is an issue when running `rustfix` afterwards. So in case this is an item that is defined in both `std` and `core`, we need to check if the crate is `no_std` to emit the right path.

r? `@llogiq`

changelog: Correctly suggest std or core path depending if this is a `no_std` crate

1 files changed, 82 insertions, 0 deletions

diff --git a/tests/ui/mem_replace_no_std.fixed b/tests/ui/mem_replace_no_std.fixed
new file mode 100644
index 00000000000..c970f2ba281
--- /dev/null
+++ b/tests/ui/mem_replace_no_std.fixed
@@ -0,0 +1,82 @@
+#![allow(unused)]
+#![warn(
+    clippy::all,
+    clippy::style,
+    clippy::mem_replace_option_with_none,
+    clippy::mem_replace_with_default
+)]
+#![feature(lang_items)]
+#![no_std]
+
+use core::mem;
+use core::panic::PanicInfo;
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    loop {}
+}
+
+fn replace_option_with_none() {
+    let mut an_option = Some(1);
+    let _ = an_option.take();
+    let an_option = &mut Some(1);
+    let _ = an_option.take();
+}
+
+fn replace_with_default() {
+    let mut refstr = "hello";
+    let _ = core::mem::take(&mut refstr);
+
+    let mut slice: &[i32] = &[1, 2, 3];
+    let _ = core::mem::take(&mut slice);
+}
+
+// lint is disabled for primitives because in this case `take`
+// has no clear benefit over `replace` and sometimes is harder to read
+fn dont_lint_primitive() {
+    let mut pbool = true;
+    let _ = mem::replace(&mut pbool, false);
+
+    let mut pint = 5;
+    let _ = mem::replace(&mut pint, 0);
+}
+
+fn main() {
+    replace_option_with_none();
+    replace_with_default();
+    dont_lint_primitive();
+}
+
+fn issue9824() {
+    struct Foo<'a>(Option<&'a str>);
+    impl<'a> core::ops::Deref for Foo<'a> {
+        type Target = Option<&'a str>;
+
+        fn deref(&self) -> &Self::Target {
+            &self.0
+        }
+    }
+    impl<'a> core::ops::DerefMut for Foo<'a> {
+        fn deref_mut(&mut self) -> &mut Self::Target {
+            &mut self.0
+        }
+    }
+
+    struct Bar {
+        opt: Option<u8>,
+        val: u8,
+    }
+
+    let mut f = Foo(Some("foo"));
+    let mut b = Bar { opt: Some(1), val: 12 };
+
+    // replace option with none
+    let _ = f.0.take();
+    let _ = (*f).take();
+    let _ = b.opt.take();
+    // replace with default
+    let _ = mem::replace(&mut b.val, u8::default());
+}