set default for build.tidy-extra-checks to auto run all but shellcheck

src/bootstrap/src/core/build_steps/test.rs

@@ -1125,10 +1125,10 @@ impl Step for Tidy {
         if builder.config.cmd.bless() {
             cmd.arg("--bless");
         }
-        if let Some(s) =
-            builder.config.cmd.extra_checks().or(builder.config.tidy_extra_checks.as_deref())
-        {
-            cmd.arg(format!("--extra-checks={s}"));
+        let extra_checks =
+            builder.config.cmd.extra_checks().unwrap_or(builder.config.tidy_extra_checks.as_str());
+        if !extra_checks.is_empty() {
+            cmd.arg(format!("--extra-checks={extra_checks}"));
         }
         let mut args = std::env::args_os();
         if args.any(|arg| arg == OsStr::new("--")) {

src/bootstrap/src/core/config/config.rs

@@ -299,7 +299,7 @@ pub struct Config {
     /// Whether to use the precompiled stage0 libtest with compiletest.
     pub compiletest_use_stage0_libtest: bool,
     /// Default value for `--extra-checks`
-    pub tidy_extra_checks: Option<String>,
+    pub tidy_extra_checks: String,
     pub is_running_on_ci: bool,
 
     /// Cache for determining path modifications
@@ -1014,7 +1014,8 @@ impl Config {
             optimized_compiler_builtins.unwrap_or(config.channel != "dev");
         config.compiletest_diff_tool = compiletest_diff_tool;
         config.compiletest_use_stage0_libtest = compiletest_use_stage0_libtest.unwrap_or(true);
-        config.tidy_extra_checks = tidy_extra_checks;
+        config.tidy_extra_checks = tidy_extra_checks
+            .unwrap_or_else(|| "auto:js,auto:cpp,auto:py,auto:spellcheck".to_string());
 
         let download_rustc = config.download_rustc_commit.is_some();
         config.explicit_stage_from_cli = flags_stage.is_some();