There is a generic blanket impl ToString for T,
impl<T> ToString for T where
T: Display + ?Sized,
I also noticed impl ToString for char/str/String..., and for many other types in the library document https://doc.rust-lang.org/std/string/trait.ToString.html#implementors.
Does it conflict with the generic blanket impl?
Obviously it doesn't conflict since it works ☺
But you're right, it should conflict. There is a feature under development called "specialization" which will enable the compiler to resolve conflicts when multiple impl exist provided one is more specific than the others. In this case, implementing for an explicit type (char or String) is more specific than any generic impl<T> for T, so it works.
This feature is not yet stable enough for general use, but a subset of it is considered good enough for use in the Rust standard library, as you can see in the source code for impl ToString for char:
#[stable(feature = "char_to_string_specialization", since = "1.46.0")]
impl ToString for char {