Auto merge of #11456 - tom-anders:std_instead_of_core_suggestion, r=Manishearth

Add suggestions for std_instead_of_core

```
changelog: [`std_instead_of_core`]: add suggestions
```

Fixes #11446

clippy_lints/src/std_instead_of_core.rs

@@ -1,4 +1,5 @@
-use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{HirId, Path, PathSegment};
@@ -99,17 +100,17 @@ fn check_path(&mut self, cx: &LateContext<'tcx>, path: &Path<'tcx>, _: HirId) {
             && let Some(first_segment) = get_first_segment(path)
             && is_stable(cx, def_id)
         {
-            let (lint, msg, help) = match first_segment.ident.name {
+            let (lint, used_mod, replace_with) = match first_segment.ident.name {
                 sym::std => match cx.tcx.crate_name(def_id.krate) {
                     sym::core => (
                         STD_INSTEAD_OF_CORE,
-                        "used import from `std` instead of `core`",
+                        "std",
-                        "consider importing the item from `core`",
+                        "core",
                     ),
                     sym::alloc => (
                         STD_INSTEAD_OF_ALLOC,
-                        "used import from `std` instead of `alloc`",
+                        "std",
-                        "consider importing the item from `alloc`",
+                        "alloc",
                     ),
                     _ => {
                         self.prev_span = path.span;
@@ -120,8 +121,8 @@ fn check_path(&mut self, cx: &LateContext<'tcx>, path: &Path<'tcx>, _: HirId) {
                     if cx.tcx.crate_name(def_id.krate) == sym::core {
                         (
                             ALLOC_INSTEAD_OF_CORE,
-                            "used import from `alloc` instead of `core`",
+                            "alloc",
-                            "consider importing the item from `core`",
+                            "core",
                         )
                     } else {
                         self.prev_span = path.span;
@@ -131,7 +132,14 @@ fn check_path(&mut self, cx: &LateContext<'tcx>, path: &Path<'tcx>, _: HirId) {
                 _ => return,
             };
             if path.span != self.prev_span {
-                span_lint_and_help(cx, lint, path.span, msg, None, help);
+                span_lint_and_sugg(
+                    cx,
+                    lint,
+                    first_segment.ident.span,
+                    &format!("used import from `{used_mod}` instead of `{replace_with}`"),
+                    &format!("consider importing the item from `{replace_with}`"),
+                    replace_with.to_string(),
+                    Applicability::MachineApplicable);
                 self.prev_span = path.span;
             }
         }

tests/ui/std_instead_of_core.fixed

@@ -0,0 +1,62 @@
+#![warn(clippy::std_instead_of_core)]
+#![allow(unused_imports)]
+
+extern crate alloc;
+
+#[warn(clippy::std_instead_of_core)]
+fn std_instead_of_core() {
+    // Regular import
+    use core::hash::Hasher;
+    //~^ ERROR: used import from `std` instead of `core`
+    // Absolute path
+    use ::core::hash::Hash;
+    //~^ ERROR: used import from `std` instead of `core`
+    // Don't lint on `env` macro
+    use std::env;
+
+    // Multiple imports
+    use core::fmt::{Debug, Result};
+    //~^ ERROR: used import from `std` instead of `core`
+
+    // Function calls
+    let ptr = core::ptr::null::<u32>();
+    //~^ ERROR: used import from `std` instead of `core`
+    let ptr_mut = ::core::ptr::null_mut::<usize>();
+    //~^ ERROR: used import from `std` instead of `core`
+
+    // Types
+    let cell = core::cell::Cell::new(8u32);
+    //~^ ERROR: used import from `std` instead of `core`
+    let cell_absolute = ::core::cell::Cell::new(8u32);
+    //~^ ERROR: used import from `std` instead of `core`
+
+    let _ = std::env!("PATH");
+
+    // do not lint until `error_in_core` is stable
+    use std::error::Error;
+
+    // lint items re-exported from private modules, `core::iter::traits::iterator::Iterator`
+    use core::iter::Iterator;
+    //~^ ERROR: used import from `std` instead of `core`
+}
+
+#[warn(clippy::std_instead_of_alloc)]
+fn std_instead_of_alloc() {
+    // Only lint once.
+    use alloc::vec;
+    //~^ ERROR: used import from `std` instead of `alloc`
+    use alloc::vec::Vec;
+    //~^ ERROR: used import from `std` instead of `alloc`
+}
+
+#[warn(clippy::alloc_instead_of_core)]
+fn alloc_instead_of_core() {
+    use core::slice::from_ref;
+    //~^ ERROR: used import from `alloc` instead of `core`
+}
+
+fn main() {
+    std_instead_of_core();
+    std_instead_of_alloc();
+    alloc_instead_of_core();
+}

tests/ui/std_instead_of_core.rs

@@ -17,7 +17,6 @@ fn std_instead_of_core() {
     // Multiple imports
     use std::fmt::{Debug, Result};
     //~^ ERROR: used import from `std` instead of `core`
-    //~| ERROR: used import from `std` instead of `core`
 
     // Function calls
     let ptr = std::ptr::null::<u32>();

tests/ui/std_instead_of_core.stderr

@@ -2,103 +2,76 @@ error: used import from `std` instead of `core`
   --> $DIR/std_instead_of_core.rs:9:9
    |
 LL |     use std::hash::Hasher;
-   |         ^^^^^^^^^^^^^^^^^
+   |         ^^^ help: consider importing the item from `core`: `core`
    |
-   = help: consider importing the item from `core`
    = note: `-D clippy::std-instead-of-core` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::std_instead_of_core)]`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:12:9
+  --> $DIR/std_instead_of_core.rs:12:11
    |
 LL |     use ::std::hash::Hash;
-   |         ^^^^^^^^^^^^^^^^^
+   |           ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:18:20
+  --> $DIR/std_instead_of_core.rs:18:9
    |
 LL |     use std::fmt::{Debug, Result};
-   |                    ^^^^^
+   |         ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:18:27
+  --> $DIR/std_instead_of_core.rs:22:15
-   |
-LL |     use std::fmt::{Debug, Result};
-   |                           ^^^^^^
-   |
-   = help: consider importing the item from `core`
-
-error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:23:15
    |
 LL |     let ptr = std::ptr::null::<u32>();
-   |               ^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:25:19
+  --> $DIR/std_instead_of_core.rs:24:21
    |
 LL |     let ptr_mut = ::std::ptr::null_mut::<usize>();
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                     ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:29:16
+  --> $DIR/std_instead_of_core.rs:28:16
    |
 LL |     let cell = std::cell::Cell::new(8u32);
-   |                ^^^^^^^^^^^^^^^
+   |                ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:31:25
+  --> $DIR/std_instead_of_core.rs:30:27
    |
 LL |     let cell_absolute = ::std::cell::Cell::new(8u32);
-   |                         ^^^^^^^^^^^^^^^^^
+   |                           ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `core`
-  --> $DIR/std_instead_of_core.rs:40:9
+  --> $DIR/std_instead_of_core.rs:39:9
    |
 LL |     use std::iter::Iterator;
-   |         ^^^^^^^^^^^^^^^^^^^
+   |         ^^^ help: consider importing the item from `core`: `core`
-   |
-   = help: consider importing the item from `core`
 
 error: used import from `std` instead of `alloc`
-  --> $DIR/std_instead_of_core.rs:47:9
+  --> $DIR/std_instead_of_core.rs:46:9
    |
 LL |     use std::vec;
-   |         ^^^^^^^^
+   |         ^^^ help: consider importing the item from `alloc`: `alloc`
    |
-   = help: consider importing the item from `alloc`
    = note: `-D clippy::std-instead-of-alloc` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::std_instead_of_alloc)]`
 
 error: used import from `std` instead of `alloc`
-  --> $DIR/std_instead_of_core.rs:49:9
+  --> $DIR/std_instead_of_core.rs:48:9
    |
 LL |     use std::vec::Vec;
-   |         ^^^^^^^^^^^^^
+   |         ^^^ help: consider importing the item from `alloc`: `alloc`
-   |
-   = help: consider importing the item from `alloc`
 
 error: used import from `alloc` instead of `core`
-  --> $DIR/std_instead_of_core.rs:55:9
+  --> $DIR/std_instead_of_core.rs:54:9
    |
 LL |     use alloc::slice::from_ref;
-   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |         ^^^^^ help: consider importing the item from `core`: `core`
    |
-   = help: consider importing the item from `core`
    = note: `-D clippy::alloc-instead-of-core` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::alloc_instead_of_core)]`
 
-error: aborting due to 12 previous errors
+error: aborting due to 11 previous errors