Clang was released 2007 and was usable 2009/2010-ish. Rust dev started 2010.
I'm not saying the trend of having good diagnostics was started by clang, but it's a more believable than the claim that it was started by Rust.
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Rust-the-language is nice, but the Rust community feeling the need to mention Rust on every unrelated thread is a bit of a turn-off for me.