simplify check_cfg_arg impl

Author: hkBst

compiler/rustc_session/src/config/cfg.rs

@@ -9,8 +9,8 @@
 //!
 //! ## Adding a new cfg
 //!
-//! Adding a new feature requires two new symbols one for the cfg itself
-//! and the second one for the unstable feature gate, those are defined in
+//! Adding a new feature requires two new symbols: one for the cfg itself
+//! and the second one for the unstable feature gate; those are defined in
 //! `rustc_span::symbol`.
 //!
 //! As well as the following points,
@@ -107,8 +107,8 @@ pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
     //
     // The tests are in tests/ui/cfg/disallowed-cli-cfgs.rs.
 
-    // By-default all builtin cfgs are disallowed, only those are allowed:
-    //  - test: as it makes sense to the have the `test` cfg active without the builtin
+    // By default all builtin cfgs are disallowed, but these are allowed:
+    //  - test: as it makes sense to have the `test` cfg active without the builtin
     //          test harness. See Cargo `harness = false` config.
     //
     // Cargo `--cfg test`: https://github.com/rust-lang/cargo/blob/bc89bffa5987d4af8f71011c7557119b39e44a65/src/cargo/core/compiler/mod.rs#L1124

src/bootstrap/src/lib.rs

@@ -82,13 +82,13 @@ const LLD_FILE_NAMES: &[&str] = &["ld.lld", "ld64.lld", "lld-link", "wasm-ld"];
 /// Extra `--check-cfg` to add when building the compiler or tools
 /// (Mode restriction, config name, config values (if any))
 #[expect(clippy::type_complexity)] // It's fine for hard-coded list and type is explained above.
-const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, Option<&[&'static str]>)] = &[
-    (Some(Mode::Rustc), "bootstrap", None),
-    (Some(Mode::Codegen), "bootstrap", None),
-    (Some(Mode::ToolRustcPrivate), "bootstrap", None),
-    (Some(Mode::ToolStd), "bootstrap", None),
-    (Some(Mode::ToolRustcPrivate), "rust_analyzer", None),
-    (Some(Mode::ToolStd), "rust_analyzer", None),
+const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, &[&'static str])] = &[
+    (Some(Mode::Rustc), "bootstrap", &[]),
+    (Some(Mode::Codegen), "bootstrap", &[]),
+    (Some(Mode::ToolRustcPrivate), "bootstrap", &[]),
+    (Some(Mode::ToolStd), "bootstrap", &[]),
+    (Some(Mode::ToolRustcPrivate), "rust_analyzer", &[]),
+    (Some(Mode::ToolStd), "rust_analyzer", &[]),
     // Any library specific cfgs like `target_os`, `target_arch` should be put in
     // priority the `[lints.rust.unexpected_cfgs.check-cfg]` table
     // in the appropriate `library/{std,alloc,core}/Cargo.toml`

src/bootstrap/src/utils/helpers.rs

@@ -490,22 +490,13 @@ where
     })
 }
 
-/// Create a `--check-cfg` argument invocation for a given name
-/// and it's values.
-pub fn check_cfg_arg(name: &str, values: Option<&[&str]>) -> String {
-    // Creating a string of the values by concatenating each value:
-    // ',values("tvos","watchos")' or '' (nothing) when there are no values.
-    let next = match values {
-        Some(values) => {
-            let mut tmp = values.iter().flat_map(|val| [",", "\"", val, "\""]).collect::<String>();
-
-            tmp.insert_str(1, "values(");
-            tmp.push(')');
-            tmp
-        }
-        None => "".to_string(),
-    };
-    format!("--check-cfg=cfg({name}{next})")
+/// Create a `--check-cfg` argument invocation for a given name and values.
+pub fn check_cfg_arg(name: &str, values: &[&str]) -> String {
+    if values.is_empty() {
+        format!("--check-cfg=cfg({name})")
+    } else {
+        format!("--check-cfg=cfg({name},values(\"{}\"))", values.join("\",\""))
+    }
 }
 
 /// Prepares `BootstrapCommand` that runs git inside the source directory if given.