Simplify reindent_multiline() signature

- `reindent_multiline()` always returns the result of
  `reindent_multiline_inner()` which returns a `String`. Make
  `reindent_multiline()` return a `String` as well, instead of a
  systematically owned `Cow<'_, str>`.
- There is no reason for `reindent_multiline()` to force a caller to
  build a `Cow<'_, str>` instead of passing a `&str` directly,
  especially considering that a `String` will always be returned.

Also, both the input parameter and return value (of type `Cow<'_, str>`)
shared the same (elided) lifetime for no reason: this worked only because
the result was always the `Cow::Owned` variant which is compatible with
any lifetime.

As a consequence, the signature changes from:

```rust
fn reindent_multiline(s: Cow<'_, str>, …) -> Cow<'_, str> { … }
```

to

```rust
fn reindent_multiline(s: &str, …) -> String { … }
```

clippy_lints/src/copies.rs

@@ -18,7 +18,6 @@ use rustc_session::impl_lint_pass;
 use rustc_span::hygiene::walk_chain;
 use rustc_span::source_map::SourceMap;
 use rustc_span::{Span, Symbol};
-use std::borrow::Cow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -248,18 +247,18 @@ fn lint_branches_sharing_code<'tcx>(
         let first_line_span = first_line_of_span(cx, expr.span);
         let replace_span = first_line_span.with_hi(span.hi());
         let cond_span = first_line_span.until(first_block.span);
-        let cond_snippet = reindent_multiline(snippet(cx, cond_span, "_"), false, None);
+        let cond_snippet = reindent_multiline(&snippet(cx, cond_span, "_"), false, None);
         let cond_indent = indent_of(cx, cond_span);
-        let moved_snippet = reindent_multiline(snippet(cx, span, "_"), true, None);
+        let moved_snippet = reindent_multiline(&snippet(cx, span, "_"), true, None);
         let suggestion = moved_snippet.to_string() + "\n" + &cond_snippet + "{";
-        let suggestion = reindent_multiline(Cow::Borrowed(&suggestion), true, cond_indent);
+        let suggestion = reindent_multiline(&suggestion, true, cond_indent);
         (replace_span, suggestion.to_string())
     });
     let end_suggestion = res.end_span(last_block, sm).map(|span| {
-        let moved_snipped = reindent_multiline(snippet(cx, span, "_"), true, None);
+        let moved_snipped = reindent_multiline(&snippet(cx, span, "_"), true, None);
         let indent = indent_of(cx, expr.span.shrink_to_hi());
         let suggestion = "}\n".to_string() + &moved_snipped;
-        let suggestion = reindent_multiline(Cow::Borrowed(&suggestion), true, indent);
+        let suggestion = reindent_multiline(&suggestion, true, indent);
 
         let span = span.with_hi(last_block.span.hi());
         // Improve formatting if the inner block has indention (i.e. normal Rust formatting)

clippy_lints/src/entry.rs

@@ -135,8 +135,8 @@ impl<'tcx> LateLintPass<'tcx> for HashMapPass {
                 format!(
                     "match {map_str}.entry({key_str}) {{\n{indent_str}    {entry}::{then_entry} => {}\n\
                         {indent_str}    {entry}::{else_entry} => {}\n{indent_str}}}",
-                    reindent_multiline(then_str.into(), true, Some(4 + indent_str.len())),
-                    reindent_multiline(else_str.into(), true, Some(4 + indent_str.len())),
+                    reindent_multiline(&then_str, true, Some(4 + indent_str.len())),
+                    reindent_multiline(&else_str, true, Some(4 + indent_str.len())),
                     entry = map_ty.entry_path(),
                 )
             }

clippy_lints/src/if_not_else.rs

@@ -7,7 +7,6 @@ use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
 use rustc_span::Span;
-use std::borrow::Cow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -107,7 +106,7 @@ fn make_sugg<'a>(
     els_span: Span,
     default: &'a str,
     indent_relative_to: Option<Span>,
-) -> Cow<'a, str> {
+) -> String {
     let cond_inner_snip = snippet(sess, cond_inner, default);
     let els_snip = snippet(sess, els_span, default);
     let indent = indent_relative_to.and_then(|s| indent_of(sess, s));
@@ -130,5 +129,5 @@ fn make_sugg<'a>(
         _ => String::new(),
     };
 
-    reindent_multiline(suggestion.into(), true, indent)
+    reindent_multiline(&suggestion, true, indent)
 }

clippy_lints/src/matches/manual_unwrap_or.rs

@@ -113,7 +113,7 @@ fn lint<'tcx>(
     or_body_snippet: &str,
     indent: usize,
 ) {
-    let reindented_or_body = reindent_multiline(or_body_snippet.into(), true, Some(indent));
+    let reindented_or_body = reindent_multiline(or_body_snippet, true, Some(indent));
 
     let mut app = Applicability::MachineApplicable;
     let suggestion = sugg::Sugg::hir_with_context(cx, scrutinee, expr.span.ctxt(), "..", &mut app).maybe_par();

clippy_lints/src/methods/case_sensitive_file_extension_comparisons.rs

@@ -57,14 +57,13 @@ pub(super) fn check<'tcx>(
                     };
 
                     let suggestion_source = reindent_multiline(
-                        format!(
+                        &format!(
                             "std::path::Path::new({})
                                 .extension()
                                 .map_or(false, |ext| ext.eq_ignore_ascii_case(\"{}\"))",
                             recv_source,
                             ext_str.strip_prefix('.').unwrap()
-                        )
-                        .into(),
+                        ),
                         true,
                         Some(indent_of(cx, call_span).unwrap_or(0) + 4),
                     );

clippy_lints/src/methods/filter_map.rs

@@ -12,7 +12,6 @@ use rustc_lint::LateContext;
 use rustc_middle::ty::adjustment::Adjust;
 use rustc_span::Span;
 use rustc_span::symbol::{Ident, Symbol, sym};
-use std::borrow::Cow;
 
 use super::{MANUAL_FILTER_MAP, MANUAL_FIND_MAP, OPTION_FILTER_MAP, RESULT_FILTER_MAP};
 
@@ -302,7 +301,7 @@ pub(super) fn check(
             filter_span.with_hi(expr.span.hi()),
             "`filter` for `Some` followed by `unwrap`",
             "consider using `flatten` instead",
-            reindent_multiline(Cow::Borrowed("flatten()"), true, indent_of(cx, map_span)).into_owned(),
+            reindent_multiline("flatten()", true, indent_of(cx, map_span)),
             Applicability::MachineApplicable,
         );
 
@@ -316,7 +315,7 @@ pub(super) fn check(
             filter_span.with_hi(expr.span.hi()),
             "`filter` for `Ok` followed by `unwrap`",
             "consider using `flatten` instead",
-            reindent_multiline(Cow::Borrowed("flatten()"), true, indent_of(cx, map_span)).into_owned(),
+            reindent_multiline("flatten()", true, indent_of(cx, map_span)),
             Applicability::MachineApplicable,
         );
 

clippy_lints/src/methods/iter_filter.rs

@@ -12,7 +12,6 @@ use rustc_hir as hir;
 use rustc_hir::QPath;
 use rustc_span::Span;
 use rustc_span::symbol::{Ident, Symbol, sym};
-use std::borrow::Cow;
 
 ///
 /// Returns true if the expression is a method call to `method_name`
@@ -181,7 +180,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, filter_arg: &hir
             filter_span.with_hi(expr.span.hi()),
             "`filter` for `is_ok` on iterator over `Result`s",
             "consider using `flatten` instead",
-            reindent_multiline(Cow::Borrowed("flatten()"), true, indent_of(cx, filter_span)).into_owned(),
+            reindent_multiline("flatten()", true, indent_of(cx, filter_span)),
             Applicability::HasPlaceholders,
         ),
         Some(FilterType::IsSome) => span_lint_and_sugg(
@@ -190,7 +189,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, filter_arg: &hir
             filter_span.with_hi(expr.span.hi()),
             "`filter` for `is_some` on iterator over `Option`",
             "consider using `flatten` instead",
-            reindent_multiline(Cow::Borrowed("flatten()"), true, indent_of(cx, filter_span)).into_owned(),
+            reindent_multiline("flatten()", true, indent_of(cx, filter_span)),
             Applicability::HasPlaceholders,
         ),
     }

clippy_lints/src/methods/manual_ok_or.rs

@@ -27,7 +27,7 @@ pub(super) fn check<'tcx>(
         && let Some(err_arg_snippet) = err_arg.span.get_source_text(cx)
         && let Some(indent) = indent_of(cx, expr.span)
     {
-        let reindented_err_arg_snippet = reindent_multiline(err_arg_snippet.as_str().into(), true, Some(indent + 4));
+        let reindented_err_arg_snippet = reindent_multiline(err_arg_snippet.as_str(), true, Some(indent + 4));
         span_lint_and_sugg(
             cx,
             MANUAL_OK_OR,

clippy_lints/src/needless_continue.rs

@@ -356,7 +356,7 @@ fn suggestion_snippet_for_continue_inside_else(cx: &EarlyContext<'_>, data: &Lin
         .iter()
         .map(|stmt| {
             let span = cx.sess().source_map().stmt_span(stmt.span, data.loop_block.span);
-            let snip = snippet_block(cx, span, "..", None).into_owned();
+            let snip = snippet_block(cx, span, "..", None);
             snip.lines()
                 .map(|line| format!("{}{line}", " ".repeat(indent)))
                 .collect::<Vec<_>>()

clippy_lints/src/redundant_else.rs

@@ -7,7 +7,6 @@ use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::declare_lint_pass;
 use rustc_span::Span;
-use std::borrow::Cow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -164,14 +163,9 @@ fn extract_else_block(mut block: &str) -> String {
     block.trim_end().to_string()
 }
 
-fn make_sugg<'a>(
-    cx: &EarlyContext<'_>,
-    els_span: Span,
-    default: &'a str,
-    indent_relative_to: Option<Span>,
-) -> Cow<'a, str> {
+fn make_sugg(cx: &EarlyContext<'_>, els_span: Span, default: &str, indent_relative_to: Option<Span>) -> String {
     let extracted = extract_else_block(&snippet(cx, els_span, default));
     let indent = indent_relative_to.and_then(|s| indent_of(cx, s));
 
-    reindent_multiline(extracted.into(), false, indent)
+    reindent_multiline(&extracted, false, indent)
 }

clippy_lints/src/unit_types/unit_arg.rs

@@ -177,16 +177,15 @@ fn fmt_stmts_and_call(
     stmts_and_call.push(call_snippet_with_replacements);
     stmts_and_call = stmts_and_call
         .into_iter()
-        .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
+        .map(|v| reindent_multiline(&v, true, Some(call_expr_indent)))
         .collect();
 
     let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
     // expr is not in a block statement or result expression position, wrap in a block
     let parent_node = cx.tcx.parent_hir_node(call_expr.hir_id);
     if !matches!(parent_node, Node::Block(_)) && !matches!(parent_node, Node::Stmt(_)) {
         let block_indent = call_expr_indent + 4;
-        stmts_and_call_snippet =
-            reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
+        stmts_and_call_snippet = reindent_multiline(&stmts_and_call_snippet, true, Some(block_indent));
         stmts_and_call_snippet = format!(
             "{{\n{}{}\n{}}}",
             " ".repeat(block_indent),

clippy_utils/src/source.rs

@@ -307,7 +307,7 @@ pub fn expr_block(
         && let ExprKind::Block(block, _) = expr.kind
         && block.rules != BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
     {
-        format!("{code}")
+        code
     } else {
         // FIXME: add extra indent for the unsafe blocks:
         //     original code:   unsafe { ... }
@@ -420,11 +420,10 @@ pub fn position_before_rarrow(s: &str) -> Option<usize> {
 }
 
 /// Reindent a multiline string with possibility of ignoring the first line.
-#[expect(clippy::needless_pass_by_value)]
-pub fn reindent_multiline(s: Cow<'_, str>, ignore_first: bool, indent: Option<usize>) -> Cow<'_, str> {
-    let s_space = reindent_multiline_inner(&s, ignore_first, indent, ' ');
+pub fn reindent_multiline(s: &str, ignore_first: bool, indent: Option<usize>) -> String {
+    let s_space = reindent_multiline_inner(s, ignore_first, indent, ' ');
     let s_tab = reindent_multiline_inner(&s_space, ignore_first, indent, '\t');
-    reindent_multiline_inner(&s_tab, ignore_first, indent, ' ').into()
+    reindent_multiline_inner(&s_tab, ignore_first, indent, ' ')
 }
 
 fn reindent_multiline_inner(s: &str, ignore_first: bool, indent: Option<usize>, ch: char) -> String {
@@ -552,42 +551,37 @@ pub fn snippet_opt(sess: &impl HasSession, span: Span) -> Option<String> {
 ///     } // aligned with `if`
 /// ```
 /// Note that the first line of the snippet always has 0 indentation.
-pub fn snippet_block<'a>(
-    sess: &impl HasSession,
-    span: Span,
-    default: &'a str,
-    indent_relative_to: Option<Span>,
-) -> Cow<'a, str> {
+pub fn snippet_block(sess: &impl HasSession, span: Span, default: &str, indent_relative_to: Option<Span>) -> String {
     let snip = snippet(sess, span, default);
     let indent = indent_relative_to.and_then(|s| indent_of(sess, s));
-    reindent_multiline(snip, true, indent)
+    reindent_multiline(&snip, true, indent)
 }
 
 /// Same as `snippet_block`, but adapts the applicability level by the rules of
 /// `snippet_with_applicability`.
-pub fn snippet_block_with_applicability<'a>(
+pub fn snippet_block_with_applicability(
     sess: &impl HasSession,
     span: Span,
-    default: &'a str,
+    default: &str,
     indent_relative_to: Option<Span>,
     applicability: &mut Applicability,
-) -> Cow<'a, str> {
+) -> String {
     let snip = snippet_with_applicability(sess, span, default, applicability);
     let indent = indent_relative_to.and_then(|s| indent_of(sess, s));
-    reindent_multiline(snip, true, indent)
+    reindent_multiline(&snip, true, indent)
 }
 
-pub fn snippet_block_with_context<'a>(
+pub fn snippet_block_with_context(
     sess: &impl HasSession,
     span: Span,
     outer: SyntaxContext,
-    default: &'a str,
+    default: &str,
     indent_relative_to: Option<Span>,
     app: &mut Applicability,
-) -> (Cow<'a, str>, bool) {
+) -> (String, bool) {
     let (snip, from_macro) = snippet_with_context(sess, span, outer, default, app);
     let indent = indent_relative_to.and_then(|s| indent_of(sess, s));
-    (reindent_multiline(snip, true, indent), from_macro)
+    (reindent_multiline(&snip, true, indent), from_macro)
 }
 
 /// Same as `snippet_with_applicability`, but first walks the span up to the given context.
@@ -745,11 +739,11 @@ mod test {
 
     #[test]
     fn test_reindent_multiline_single_line() {
-        assert_eq!("", reindent_multiline("".into(), false, None));
-        assert_eq!("...", reindent_multiline("...".into(), false, None));
-        assert_eq!("...", reindent_multiline("    ...".into(), false, None));
-        assert_eq!("...", reindent_multiline("\t...".into(), false, None));
-        assert_eq!("...", reindent_multiline("\t\t...".into(), false, None));
+        assert_eq!("", reindent_multiline("", false, None));
+        assert_eq!("...", reindent_multiline("...", false, None));
+        assert_eq!("...", reindent_multiline("    ...", false, None));
+        assert_eq!("...", reindent_multiline("\t...", false, None));
+        assert_eq!("...", reindent_multiline("\t\t...", false, None));
     }
 
     #[test]
@@ -764,7 +758,7 @@ mod test {
             y
         } else {
             z
-        }".into(), false, None));
+        }", false, None));
         assert_eq!("\
     if x {
     \ty
@@ -774,7 +768,7 @@ mod test {
         \ty
         } else {
         \tz
-        }".into(), false, None));
+        }", false, None));
     }
 
     #[test]
@@ -791,7 +785,7 @@ mod test {
 
         } else {
             z
-        }".into(), false, None));
+        }", false, None));
     }
 
     #[test]
@@ -807,6 +801,6 @@ mod test {
         y
     } else {
         z
-    }".into(), true, Some(8)));
+    }", true, Some(8)));
     }
 }