[abo3losh1]

Errorf formats its arguments twice. It runs them through formatAllWithLineFlag and then passes the result to pp.Sprintf, which pretty prints the already formatted strings again.

p := pp.New()
p.SetColoringEnabled(false)
p.Sprintf("val=%v", 42)        // val=42
p.Errorf("val=%v", 42).Error() // val="42"

With colors on, the error text has the escape codes quoted and colored again (val=\x1b[31m\x1b[1m"\x1b[0m...), and with WithLineInfo it gets two line info headers, the outer one pointing at pp.go instead of the caller.

This came in with #106. Before that Errorf was errors.New(pp.Sprintf(format, a...)), which was fine because the arguments were not formatted first. The fix uses fmt.Sprintf here, same as Sprintf and Fprintf do.

Added TestErrorf, which checks the plain output and that the colored output matches Sprintf. Both fail before the fix. go test and go vet pass.

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