fix(cmd): injects version at build time

Couple of past released missed aligning harcoded `main.version` variable
with the current tag. This results in confusing output of `gci --version`,
where e.g. last release (tagged with `v0.13.5`) prints `0.13.4`.

```shell
❯ go install github.com/daixiang0/[email protected]
❯ gci --version
gci version 0.13.4
```

With this change, `main.Version` is calculated at build time and
injected. Therefore it  will always contain the tag that it was
built from (or `devel` if it's built from untagged commit).

```shell
❯ make build
❯ ./dist/gci -v
gci version devel
❯ git tag v0.13.13
❯ make build
BIN_OUTPUT: dist/gci
❯ ./dist/gci -v
gci version 0.13.13
```

With the upcoming `go1.24` release this information can be obtained from
`runtime/debug.BuildInfo.Main.Version` [1].

This will simplify the process even further.

[1] golang/go#50603 (comment)

Signed-off-by: bartoszmajsak <[email protected]>

Makefile

@@ -8,8 +8,18 @@ clean:
 	@echo BIN_OUTPUT: ${BIN_OUTPUT}
 	@rm -rf dist cover.out
 
+VERSION ?= $(shell git describe --tags --abbrev=0 2>/dev/null || echo "v0.0.0")
+GIT_TAG := $(shell git describe --tags --abbrev=0 --exact-match > /dev/null 2>&1; echo $$?)
+
+ifneq ($(GIT_TAG),0)
+	ifeq ($(origin VERSION),file)
+		VERSION := devel
+	endif
+endif
+
+LDFLAGS ?= -w -X main.Version=${VERSION}
 build: clean
-	@go build -v -trimpath -o ${BIN_OUTPUT} .
+	@go build -v -trimpath -ldflags "${LDFLAGS}" -o ${BIN_OUTPUT} .
 
 test: clean
 	@go test -v -count=1 -cover ./...

main.go

@@ -1,15 +1,15 @@
 package main
 
 import (
-	"os"
-
 	"github.com/daixiang0/gci/cmd/gci"
+	"os"
+	"strings"
 )
 
-var version = "0.13.4"
+var Version = "0.0.0"
 
 func main() {
-	e := gci.NewExecutor(version)
+	e := gci.NewExecutor(strings.TrimPrefix(Version, "v"))
 
 	err := e.Execute()
 	if err != nil {