Improve: use list command to resolve relative import path

[leventeliu]

Why this change?

With a very simple repository for demonstration:

git clone https://github.com/leventeliu/godepgraph-demo.git
cd godepgraph-demo

Initially, when I was trying to get dep-graph inside a go module (given filter -o <prefix>) with a relative import path syntax, godepgraph gave an empty result:

$ godepgraph -o github.com/leventeliu ./cmd/nop
digraph godep {
splines=ortho
nodesep=0.4
ranksep=0.8
node [shape="box",style="rounded,filled"]
edge [arrowsize="0.5"]
}

After some code reading, I found the correct way to do it cloud be:

$ godepgraph -o .,github.com/leventeliu ./cmd/nop
digraph godep {
splines=ortho
nodesep=0.4
ranksep=0.8
node [shape="box",style="rounded,filled"]
edge [arrowsize="0.5"]
"./cmd/nop" [label="./cmd/nop" color="paleturquoise" URL="https://godoc.org/./cmd/nop" target="_blank"];
"./cmd/nop" -> "github.com/leventeliu/godepgraph-demo/a";
"./cmd/nop" -> "github.com/leventeliu/godepgraph-demo/b";
"github.com/leventeliu/godepgraph-demo/a" [label="github.com/leventeliu/godepgraph-demo/a" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/a" target="_blank"];
"github.com/leventeliu/godepgraph-demo/b" [label="github.com/leventeliu/godepgraph-demo/b" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/b" target="_blank"];
}

But it's weird, isn't it? The problem here is that the relative path ./cmd/nop could (and should) be resolved as a full package path github.com/leventeliu/godepgraph-demo/cmd/nop, which will not be ignored by the filter -o github.com/leventeliu.

And after I tried the list command:

$ go list ./cmd/nop
github.com/leventeliu/godepgraph-demo/cmd/nop

I thought this is the proper way to solve the problem.

List command is implemented by an internal package, which will be tricky to call directly. Alternatively, I use an os/exec.Command to call go list and pass the parent environment to the command (any better idea?)

Now it works well:

$ godepgraph -o github.com/leventeliu ./cmd/nop
digraph godep {
splines=ortho
nodesep=0.4
ranksep=0.8
node [shape="box",style="rounded,filled"]
edge [arrowsize="0.5"]
"github.com/leventeliu/godepgraph-demo/a" [label="github.com/leventeliu/godepgraph-demo/a" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/a" target="_blank"];
"github.com/leventeliu/godepgraph-demo/b" [label="github.com/leventeliu/godepgraph-demo/b" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/b" target="_blank"];
"github.com/leventeliu/godepgraph-demo/cmd/nop" [label="github.com/leventeliu/godepgraph-demo/cmd/nop" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/cmd/nop" target="_blank"];
"github.com/leventeliu/godepgraph-demo/cmd/nop" -> "github.com/leventeliu/godepgraph-demo/a";
"github.com/leventeliu/godepgraph-demo/cmd/nop" -> "github.com/leventeliu/godepgraph-demo/b";
}

This improvement applies to the case when you are working with "GOPATH mode", instead of go module, too.

Also, this implies a special pattern /... will be supported:

$ godepgraph -o github.com/leventeliu ./...
digraph godep {
splines=ortho
nodesep=0.4
ranksep=0.8
node [shape="box",style="rounded,filled"]
edge [arrowsize="0.5"]
"github.com/leventeliu/godepgraph-demo/a" [label="github.com/leventeliu/godepgraph-demo/a" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/a" target="_blank"];
"github.com/leventeliu/godepgraph-demo/b" [label="github.com/leventeliu/godepgraph-demo/b" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/b" target="_blank"];
"github.com/leventeliu/godepgraph-demo/cmd/nop" [label="github.com/leventeliu/godepgraph-demo/cmd/nop" color="paleturquoise" URL="https://godoc.org/github.com/leventeliu/godepgraph-demo/cmd/nop" target="_blank"];
"github.com/leventeliu/godepgraph-demo/cmd/nop" -> "github.com/leventeliu/godepgraph-demo/a";
"github.com/leventeliu/godepgraph-demo/cmd/nop" -> "github.com/leventeliu/godepgraph-demo/b";
}