No warning if filter argument has no matches.

[prattmic]

Please answer these questions before submitting your issue. Thanks!

What version of pprof are you using?

If you are using pprof via go tool pprof, what's your go env output?
If you run pprof from GitHub, what's the Git revision?

923b5ab (latest HEAD)

What operating system and processor architecture are you using?

Linux, amd64

What did you do?

If possible, provide a recipe for reproducing the error.
Attaching a profile you are trying to analyze is good.

Attempt to disasm, list, peek a symbol that doesn't exist.

What did you expect to see?

An explanation that there are no matching symbols. Something like:

$ ./pprof /tmp/cpu.pprof
File: runtime.test
Type: cpu
Time: May 11, 2021 at 12:26pm (EDT)
Duration: 12.01s, Total samples = 36.44s (303.40%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) disasm blargity
no matches found for regexp: blargity 

What did you see instead?

$ ./pprof /tmp/cpu.pprof
File: runtime.test
Type: cpu
Time: May 11, 2021 at 12:26pm (EDT)
Duration: 12.01s, Total samples = 36.44s (303.40%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) disasm blargity
Total: 36.44s

To a user that doesn't fully understand this behavior, it is rather confusing to only get a "total" with no other output.

Note that commands with a focus argument do display a warning (in red):

(pprof) top blargity
Focus expression matched no samples
Active filters:
   focus=blargity
Showing nodes accounting for 0, 0% of 36.44s total
      flat  flat%   sum%        cum   cum%

I can send a simple CL to add a warning to the few commands with an argument.