My only concern with the idea of syntax highlighting all code in compiler output is that the colorized output we already have might become less effective. In particular, messages pointing at multiline code spans are legible in large part because the arrows pointing at the start and end of the span are colored and the actual code is not.
If we reserve the “most eyecatching” colors for the non-code parts of the output (i.e., what we colorize today), how many “portable colors” would we have left over to do syntax highlighting with? Your test screenshots (from Syntax highlighting in all compiler output?) look excellent to me, but they do appear to be “just code”. Could we see some more complex examples, e.g. a full cargo build run that results in an error message with multiline spans?
And let’s try to avoid debating whether the compiler does or should follow certain philosophies or whether completely unrelated features like internationalized output should be implemented. Arguing those points here is, at best, a distraction.
