Don't make string mod public, make a hidden _export module instead.

Author: Dirbaio

src/lib.rs

@@ -97,7 +97,7 @@ mod histbuf;
 mod indexmap;
 mod indexset;
 mod linear_map;
-pub mod string;
+mod string;
 mod vec;
 
 #[cfg(feature = "serde")]
@@ -134,3 +134,10 @@ pub mod spsc;
 mod ufmt;
 
 mod sealed;
+
+/// Implementation details for macros.
+/// Do not use. Used for macros only. Not covered by semver guarantees.
+#[doc(hidden)]
+pub mod _export {
+    pub use crate::string::format;
+}

src/string.rs

@@ -637,11 +637,11 @@ macro_rules! format {
     // Without semicolon as separator to disambiguate between arms, Rust just
     // chooses the first so that the format string would land in $max.
     ($max:expr; $($arg:tt)*) => {{
-        let res = $crate::string::format::<$max>(core::format_args!($($arg)*));
+        let res = $crate::_export::format::<$max>(core::format_args!($($arg)*));
         res
     }};
     ($($arg:tt)*) => {{
-        let res = $crate::string::format(core::format_args!($($arg)*));
+        let res = $crate::_export::format(core::format_args!($($arg)*));
         res
     }};
 }