Upgrade to Rust 1.86 and bump MSRV to 1.84 (#17171)

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## Summary

I decided to disable the new
[`needless_continue`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue)
rule because I often found the explicit `continue` more readable over an
empty block or having to invert the condition of an other branch.


## Test Plan

`cargo test`

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_dev/src/generate_docs.rs

@@ -2,6 +2,7 @@
 #![allow(clippy::print_stdout, clippy::print_stderr)]
 
 use std::collections::HashSet;
+use std::fmt::Write as _;
 use std::fs;
 use std::path::PathBuf;
 
@@ -29,8 +30,7 @@ pub(crate) fn main(args: &Args) -> Result<()> {
         if let Some(explanation) = rule.explanation() {
             let mut output = String::new();
 
-            output.push_str(&format!("# {} ({})", rule.as_ref(), rule.noqa_code()));
-            output.push('\n');
+            let _ = writeln!(&mut output, "# {} ({})", rule.as_ref(), rule.noqa_code());
 
             let (linter, _) = Linter::parse_code(&rule.noqa_code().to_string()).unwrap();
             if linter.url().is_some() {
@@ -49,11 +49,12 @@ pub(crate) fn main(args: &Args) -> Result<()> {
                     common_prefix.to_lowercase()
                 );
 
-                output.push_str(&format!(
+                let _ = write!(
+                    output,
                     "Derived from the **[{}](../rules.md#{})** linter.",
                     linter.name(),
-                    anchor
-                ));
+                    anchor,
+                );
                 output.push('\n');
                 output.push('\n');
             }
@@ -155,8 +156,8 @@ fn process_documentation(documentation: &str, out: &mut String, rule_name: &str)
                 }
 
                 let anchor = option.replace('.', "_");
-                out.push_str(&format!("- [`{option}`][{option}]\n"));
-                after.push_str(&format!("[{option}]: ../settings.md#{anchor}\n"));
+                let _ = writeln!(out, "- [`{option}`][{option}]");
+                let _ = writeln!(&mut after, "[{option}]: ../settings.md#{anchor}");
                 referenced_options.insert(option);
 
                 continue;
@@ -171,7 +172,7 @@ fn process_documentation(documentation: &str, out: &mut String, rule_name: &str)
         if let Some(OptionEntry::Field(field)) = Options::metadata().find(option) {
             if referenced_options.insert(option) {
                 let anchor = option.replace('.', "_");
-                after.push_str(&format!("[{option}]: ../settings.md#{anchor}\n"));
+                let _ = writeln!(&mut after, "[{option}]: ../settings.md#{anchor}");
             }
             if field.deprecated.is_some() {
                 eprintln!("Rule {rule_name} references deprecated option {option}.");

crates/ruff_dev/src/generate_options.rs

@@ -98,17 +98,16 @@ fn emit_field(output: &mut String, name: &str, field: &OptionField, parents: &[S
     let parents_anchor = parents.iter().filter_map(|parent| parent.name()).join("_");
 
     if parents_anchor.is_empty() {
-        output.push_str(&format!(
-            "{header_level} [`{name}`](#{name}) {{: #{name} }}\n"
-        ));
+        let _ = writeln!(output, "{header_level} [`{name}`](#{name}) {{: #{name} }}");
     } else {
-        output.push_str(&format!(
-            "{header_level} [`{name}`](#{parents_anchor}_{name}) {{: #{parents_anchor}_{name} }}\n"
-        ));
+        let _ =
+            writeln!(output,
+            "{header_level} [`{name}`](#{parents_anchor}_{name}) {{: #{parents_anchor}_{name} }}"
+        );
 
         // the anchor used to just be the name, but now it's the group name
         // for backwards compatibility, we need to keep the old anchor
-        output.push_str(&format!("<span id=\"{name}\"></span>\n"));
+        let _ = writeln!(output, "<span id=\"{name}\"></span>");
     }
 
     output.push('\n');
@@ -132,9 +131,9 @@ fn emit_field(output: &mut String, name: &str, field: &OptionField, parents: &[S
 
     output.push_str(field.doc);
     output.push_str("\n\n");
-    output.push_str(&format!("**Default value**: `{}`\n", field.default));
+    let _ = writeln!(output, "**Default value**: `{}`", field.default);
     output.push('\n');
-    output.push_str(&format!("**Type**: `{}`\n", field.value_type));
+    let _ = writeln!(output, "**Type**: `{}`", field.value_type);
     output.push('\n');
     output.push_str("**Example usage**:\n\n");
     output.push_str(&format_tab(

crates/ruff_dev/src/generate_rules_table.rs

@@ -5,6 +5,7 @@
 use itertools::Itertools;
 use ruff_linter::codes::RuleGroup;
 use std::borrow::Cow;
+use std::fmt::Write;
 use strum::IntoEnumIterator;
 
 use ruff_diagnostics::FixAvailability;
@@ -78,7 +79,8 @@ fn generate_table(table_out: &mut String, rules: impl IntoIterator<Item = Rule>,
         }
 
         #[allow(clippy::or_fun_call)]
-        table_out.push_str(&format!(
+        let _ = write!(
+            table_out,
             "| {ss}{0}{1}{se} {{ #{0}{1} }} | {ss}{2}{se} | {ss}{3}{se} | {ss}{4}{se} |",
             linter.common_prefix(),
             linter.code_for_rule(rule).unwrap(),
@@ -88,7 +90,7 @@ fn generate_table(table_out: &mut String, rules: impl IntoIterator<Item = Rule>,
                 .unwrap_or(format_args!("{rule_name}")),
             message,
             tokens,
-        ));
+        );
         table_out.push('\n');
     }
     table_out.push('\n');
@@ -101,29 +103,30 @@ pub(crate) fn generate() -> String {
     table_out.push_str("### Legend");
     table_out.push('\n');
 
-    table_out.push_str(&format!(
+    let _ = write!(
+        &mut table_out,
         "{SPACER}{STABLE_SYMBOL}{SPACER} The rule is stable."
-    ));
+    );
     table_out.push_str("<br />");
 
-    table_out.push_str(&format!(
+    let _ = write!(&mut table_out,
         "{SPACER}{PREVIEW_SYMBOL}{SPACER} The rule is unstable and is in [\"preview\"](faq.md#what-is-preview)."
-    ));
+    );
     table_out.push_str("<br />");
 
-    table_out.push_str(&format!(
+    let _ = write!(&mut table_out,
         "{SPACER}{WARNING_SYMBOL}{SPACER} The rule has been deprecated and will be removed in a future release."
-    ));
+    );
     table_out.push_str("<br />");
 
-    table_out.push_str(&format!(
+    let _ = write!(&mut table_out,
         "{SPACER}{REMOVED_SYMBOL}{SPACER} The rule has been removed only the documentation is available."
-    ));
+    );
     table_out.push_str("<br />");
 
-    table_out.push_str(&format!(
+    let _ = write!(&mut table_out,
         "{SPACER}{FIX_SYMBOL}{SPACER} The rule is automatically fixable by the `--fix` command-line option."
-    ));
+    );
     table_out.push_str("<br />");
     table_out.push('\n');
 
@@ -137,7 +140,7 @@ pub(crate) fn generate() -> String {
                 .join(", "),
             prefix => prefix.to_string(),
         };
-        table_out.push_str(&format!("### {} ({codes_csv})", linter.name()));
+        let _ = write!(&mut table_out, "### {} ({codes_csv})", linter.name());
         table_out.push('\n');
         table_out.push('\n');
 
@@ -147,7 +150,8 @@ pub(crate) fn generate() -> String {
                 .split('/')
                 .next()
                 .unwrap();
-            table_out.push_str(&format!(
+            let _ = write!(
+                table_out,
                 "For more, see [{}]({}) on {}.",
                 linter.name(),
                 url,
@@ -160,17 +164,18 @@ pub(crate) fn generate() -> String {
                         linter.name()
                     ),
                 }
-            ));
+            );
             table_out.push('\n');
             table_out.push('\n');
         }
 
         if Options::metadata().has(&format!("lint.{}", linter.name())) {
-            table_out.push_str(&format!(
+            let _ = write!(
+                table_out,
                 "For related settings, see [{}](settings.md#lint{}).",
                 linter.name(),
                 linter.name(),
-            ));
+            );
             table_out.push('\n');
             table_out.push('\n');
         }
@@ -200,10 +205,10 @@ pub(crate) fn generate() -> String {
                     let UpstreamCategoryAndPrefix { category, prefix } = opt.unwrap();
                     match codes_csv.as_str() {
                         "PL" => {
-                            table_out.push_str(&format!("#### {category} ({codes_csv}{prefix})"));
+                            let _ = write!(table_out, "#### {category} ({codes_csv}{prefix})");
                         }
                         _ => {
-                            table_out.push_str(&format!("#### {category} ({prefix})"));
+                            let _ = write!(table_out, "#### {category} ({prefix})");
                         }
                     }
                 }