[closure]

I don't buy this definition at all.

First, the "semantics" had better not change, either by an optimizing or non-optimizing compiler, or you've got a miscompile.

Second, I've seen several source-to-source compilers (that the proponents of the term transpiler would certainly call transpilers) that do non-trivial transformation, e.g. to try to capture certain idioms, or that are required as a result of an "impedance mismatch" between the languages.