add suggestions to rc_clone_in_vec_init

clippy_lints/src/rc_clone_in_vec_init.rs

@@ -1,11 +1,13 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::VecArgs;
 use clippy_utils::last_path_segment;
-use clippy_utils::macros::{root_macro_call_first_node, MacroCall};
+use clippy_utils::macros::root_macro_call_first_node;
+use clippy_utils::source::{indent_of, snippet};
+use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir::{Expr, ExprKind, QPath, TyKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::{sym, Symbol};
+use rustc_span::{sym, Span, Symbol};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -47,27 +49,107 @@
 impl LateLintPass<'_> for RcCloneInVecInit {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
         let Some(macro_call) = root_macro_call_first_node(cx, expr) else { return; };
-        let Some(VecArgs::Repeat(elem, _)) = VecArgs::hir(cx, expr) else { return; };
+        let Some(VecArgs::Repeat(elem, len)) = VecArgs::hir(cx, expr) else { return; };
         let Some(symbol) = new_reference_call(cx, elem) else { return; };
+        let lint_span = macro_call.span;
+        let symbol_name = symbol.as_str();
+        let len_snippet = snippet(cx, len.span, "..");
+        let elem_snippet = elem_snippet(cx, elem, symbol_name);
+        let indentation = indent_of(cx, lint_span).unwrap_or(0);
+        let lint_suggestions =
+            construct_lint_suggestions(lint_span, symbol_name, &elem_snippet, len_snippet.as_ref(), indentation);
 
-        emit_lint(cx, symbol, &macro_call);
+        emit_lint(cx, symbol, lint_span, &lint_suggestions);
     }
 }
 
-fn emit_lint(cx: &LateContext<'_>, symbol: Symbol, macro_call: &MacroCall) {
+struct LintSuggestion {
+    span: Span,
+    message: String,
+    suggestion: String,
+    applicability: Applicability,
+}
+
+impl LintSuggestion {
+    fn span_suggestion(&self, diag: &mut Diagnostic) {
+        diag.span_suggestion(self.span, &self.message, &self.suggestion, self.applicability);
+    }
+}
+
+fn construct_lint_suggestions(
+    span: Span,
+    symbol_name: &str,
+    elem_snippet: &str,
+    len_snippet: &str,
+    indentation: usize,
+) -> Vec<LintSuggestion> {
+    let indentation = " ".repeat(indentation);
+    let loop_init_suggestion = loop_init_suggestion(elem_snippet, len_snippet, &indentation);
+    let extract_suggestion = extract_suggestion(elem_snippet, len_snippet, &indentation);
+
+    vec![
+        LintSuggestion {
+            span,
+            message: format!("consider initializing each `{symbol_name}` element individually"),
+            suggestion: loop_init_suggestion,
+            applicability: Applicability::Unspecified,
+        },
+        LintSuggestion {
+            span,
+            message: format!(
+                "or if this is intentional, consider extracting the `{symbol_name}` initialization to a variable"
+            ),
+            suggestion: extract_suggestion,
+            applicability: Applicability::Unspecified,
+        },
+    ]
+}
+
+fn elem_snippet(cx: &LateContext<'_>, elem: &Expr<'_>, symbol_name: &str) -> String {
+    let mut elem_snippet = snippet(cx, elem.span, "..").to_string();
+    if elem_snippet.contains('\n') {
+        let reference_initialization = format!("{symbol_name}::new");
+        // This string must be found in `elem_snippet`, otherwise we won't be constructing the snippet in
+        // the first place.
+        let reference_initialization_end =
+            elem_snippet.find(&reference_initialization).unwrap() + reference_initialization.len();
+        elem_snippet.replace_range(reference_initialization_end.., "..");
+    }
+    elem_snippet
+}
+
+fn loop_init_suggestion(elem: &str, len: &str, indent: &str) -> String {
+    format!(
+        r#"{{
+{indent}{indent}let mut v = Vec::with_capacity({len});
+{indent}{indent}(0..{len}).for_each(|_| v.push({elem}));
+{indent}{indent}v
+{indent}}}"#
+    )
+}
+
+fn extract_suggestion(elem: &str, len: &str, indent: &str) -> String {
+    format!(
+        "{{
+{indent}{indent}let data = {elem};
+{indent}{indent}vec![data; {len}]
+{indent}}}"
+    )
+}
+
+fn emit_lint(cx: &LateContext<'_>, symbol: Symbol, lint_span: Span, lint_suggestions: &[LintSuggestion]) {
     let symbol_name = symbol.as_str();
 
     span_lint_and_then(
         cx,
         RC_CLONE_IN_VEC_INIT,
-        macro_call.span,
+        lint_span,
         &format!("calling `{symbol_name}::new` in `vec![elem; len]`"),
         |diag| {
             diag.note(format!("each element will point to the same `{symbol_name}` instance"));
-            diag.help(format!(
+            lint_suggestions
-                "if this is intentional, consider extracting the `{symbol_name}` initialization to a variable"
+                .iter()
-            ));
+                .for_each(|suggestion| suggestion.span_suggestion(diag));
-            diag.help("or if not, initialize each element individually");
         },
     );
 }

tests/ui/rc_clone_in_vec_init/arc.stderr

@@ -6,8 +6,21 @@ LL |     let v = vec![Arc::new("x".to_string()); 2];
    |
    = note: `-D clippy::rc-clone-in-vec-init` implied by `-D warnings`
    = note: each element will point to the same `Arc` instance
-   = help: if this is intentional, consider extracting the `Arc` initialization to a variable
+help: consider initializing each `Arc` element individually
-   = help: or if not, initialize each element individually
+   |
+LL ~     let v = {
+LL +         let mut v = Vec::with_capacity(2);
+LL +         (0..2).for_each(|_| v.push(Arc::new("x".to_string())));
+LL +         v
+LL ~     };
+   |
+help: or if this is intentional, consider extracting the `Arc` initialization to a variable
+   |
+LL ~     let v = {
+LL +         let data = Arc::new("x".to_string());
+LL +         vec![data; 2]
+LL ~     };
+   |
 
 error: calling `Arc::new` in `vec![elem; len]`
   --> $DIR/arc.rs:11:13
@@ -23,8 +36,21 @@ LL | |     ];
    | |_____^
    |
    = note: each element will point to the same `Arc` instance
-   = help: if this is intentional, consider extracting the `Arc` initialization to a variable
+help: consider initializing each `Arc` element individually
-   = help: or if not, initialize each element individually
+   |
+LL ~     let v = {
+LL +         let mut v = Vec::with_capacity(2);
+LL +         (0..2).for_each(|_| v.push(std::sync::Arc::new..));
+LL +         v
+LL ~     };
+   |
+help: or if this is intentional, consider extracting the `Arc` initialization to a variable
+   |
+LL ~     let v = {
+LL +         let data = std::sync::Arc::new..;
+LL +         vec![data; 2]
+LL ~     };
+   |
 
 error: aborting due to 2 previous errors
 

tests/ui/rc_clone_in_vec_init/rc.stderr

@@ -6,8 +6,21 @@ LL |     let v = vec![Rc::new("x".to_string()); 2];
    |
    = note: `-D clippy::rc-clone-in-vec-init` implied by `-D warnings`
    = note: each element will point to the same `Rc` instance
-   = help: if this is intentional, consider extracting the `Rc` initialization to a variable
+help: consider initializing each `Rc` element individually
-   = help: or if not, initialize each element individually
+   |
+LL ~     let v = {
+LL +         let mut v = Vec::with_capacity(2);
+LL +         (0..2).for_each(|_| v.push(Rc::new("x".to_string())));
+LL +         v
+LL ~     };
+   |
+help: or if this is intentional, consider extracting the `Rc` initialization to a variable
+   |
+LL ~     let v = {
+LL +         let data = Rc::new("x".to_string());
+LL +         vec![data; 2]
+LL ~     };
+   |
 
 error: calling `Rc::new` in `vec![elem; len]`
   --> $DIR/rc.rs:12:13
@@ -23,8 +36,21 @@ LL | |     ];
    | |_____^
    |
    = note: each element will point to the same `Rc` instance
-   = help: if this is intentional, consider extracting the `Rc` initialization to a variable
+help: consider initializing each `Rc` element individually
-   = help: or if not, initialize each element individually
+   |
+LL ~     let v = {
+LL +         let mut v = Vec::with_capacity(2);
+LL +         (0..2).for_each(|_| v.push(std::rc::Rc::new..));
+LL +         v
+LL ~     };
+   |
+help: or if this is intentional, consider extracting the `Rc` initialization to a variable
+   |
+LL ~     let v = {
+LL +         let data = std::rc::Rc::new..;
+LL +         vec![data; 2]
+LL ~     };
+   |
 
 error: aborting due to 2 previous errors