[sillysaurus3]

I tried to download someone's Go repo that operated on gifs, but on my machine it died with an error inside of the standard library's compression code, which failed with a cryptic message.

I spent the next 30 minutes trying to figure out how to add printline debugging to the standard library. I saw the precise line of code it was failing on, so I added some logging code above it to print out more info. Nothing happened. I tried to rebuild the file. There was no obvious way to do this. I googled for "golang recompile standard library." There was no clear, simple answer. I seemed to be expected to read all of the documentation in order to do this seemingly-simple thing. I went on Freenode and asked how to do it. Crickets.

I was being intellectually lazy, a cardinal sin. Obviously, the solution was to read the documentation, learn about GOPATH, learn how and why the source code was laid out the way it was, understand how to make my own package, then try to figure out how to make changes to existing packages.

But it's a step backwards. I'm staring at the code. I made changes to it. Why does it require a magical incantation to make those changes have an effect? Why can't it detect that the code changed, and do whatever's necessary to apply those changes? Or at least let me type "go make zlib.go" and be done with it? Yeah, "make" isn't a valid command. I'm supposed to "build" a package. But I'm not trying to build a package. I'm trying to run someone's freshly-cloned Go project.

The whole thing made me feel dumb and outdated.

[frik]

The whole GOPATH and directory magic is really bad and outdated. In almost every other language I can place my files wherever I want and write a build script.

I like everything else about Go and hope they remove that cruft from such a great language in version 2 or so. Go should learn from C/C++ in this regard.

[Nitramp]

I see that the exact other way around. With other languages, every project decides on their weird local directory layout for no good reason at all, and then everyone has to write build scripts to keep things working.

Learning from C++ builds seems like a cruel joke – not sure if trolling or not ;-)

[tumdum_]

Although I find build Go code with go tool very nice, it is in no way part of language specification. Just like in c you can build your own object files and/or archives and link them as you please. How go the tool does it is not the only possible way. See this example I've prepared on how to manually build go code: https://github.com/tumdum/go_build

You can read more detailed explanation by Dave (author of alternative Go build system - gb) here: http://dave.cheney.net/2013/10/15/how-does-the-go-build-comm...

[grey-area]

Couldn't you just copy the pkg you want to modify out to gopath/src and import it there with your modifications?

[sillysaurus3]

In this case, the project was using Go's standard image library to operate on gifs, which itself uses Go's standard compression library to perform the compression. So the stack trace on error looked like:

  > error
  > go's standard compression lib
  > go's standard gif lib
  > the project tries to write a gif to disk

It was very easy to grep the stdlib for the error message, which turned out to be in Go's compression lib. Great! I opened it up and started reading through it.

Somehow, the compression lib was receiving an invalid parameter. Therefore, either Go's standard gif library was responsible for the problem (extremely unlikely) or the project was generating some kind of "invalid" gif data, or some gif settings that Go's gif lib didn't handle correctly when writing to disk.

Printline debugging is the fastest way to figure out this type of problem. Print out everything, every single parameter, all the way up the stack. Eventually you'll spot the logic that's failing to handle the data. Trouble was, I had no clue how to modify go's stdlib. Nothing I did seemed to have any effect whatsoever.

It sounds like you're saying the solution is to copy the gif lib to my local gopath like foo/gif, rebuild it there, then modify the project to import from foo/gif instead of image/gif. Ok, cool. I'll try this, thanks!

Since the gif lib imports the compression lib, it sounds like I'll have to copy both libs, then try to modify the gif lib to use the local copy of the compression lib. Ok, sure. At least now I have a way of making progress.

The project ran on the author's machine without any problems, so I bet I'm using a different version of Go. If I could figure out which version they were using, I could just downgrade to that. Problem solved. Unfortunately, I don't think this information is present in the project's repository, which is just a single .go file. (I guess I could check when the most recent commit was, then figure out what version of Go was in use back then...)

Anyway. Thanks for your help.

[sesutton]

I'm new to go as well but seems to me what you want is to set $GOROOT_BOOTSTRAP to a copy of your $GOROOT then run $GOROOT/src/make.bash

> I'm trying to run someone's freshly-cloned Go project.

"go run x.go" will do that.