version: embed version/VERSION as version string

Since we have both version/version.go and version/VERSION to specify
version strings, both are a bit redundant.

As version/VERSION is supposed to be the source of truth now, we are
using it to derive the version informaiton we used to rely on in Packer
and its subcommands.

Note: doing this prevents us from changing the version/prerelease
through ldflags though as we derive Version/VersionPrerelease from the
rawVersion variable.

hcl2template/parser.go

@@ -157,7 +157,7 @@ func (p *Parser) Parse(filename string, varFiles []string, argVars map[string]st
 	// Before we go further, we'll check to make sure this version can read
 	// all files, so we can produce a version-related error message rather than
 	// potentially-confusing downstream errors.
-	versionDiags := cfg.CheckCoreVersionRequirements(p.CorePackerVersion)
+	versionDiags := cfg.CheckCoreVersionRequirements(p.CorePackerVersion.Core())
 	diags = append(diags, versionDiags...)
 	if versionDiags.HasErrors() {
 		return cfg, diags

version/version.go

@@ -4,6 +4,10 @@
 package version
 
 import (
+	_ "embed"
+	"fmt"
+	"strings"
+
 	"github.com/hashicorp/go-version"
 	pluginVersion "github.com/hashicorp/packer-plugin-sdk/version"
 )
@@ -16,21 +20,24 @@ var (
 	// Whether cgo is enabled or not; set at build time
 	CgoEnabled bool
 
+	//go:embed VERSION
+	rawVersion string
+
 	// The next version number that will be released. This will be updated after every release
 	// Version must conform to the format expected by github.com/hashicorp/go-version
 	// for tests to work.
 	// A pre-release marker for the version can also be specified (e.g -dev). If this is omitted
 	// The main version number that is being run at the moment.
-
-	Version = "1.11.0"
-
+	Version string
 	// A pre-release marker for the version. If this is "" (empty string)
 	// then it means that it is a final release. Otherwise, this is a pre-release
 	// such as "dev" (in development), "beta", "rc1", etc.
-
-	VersionPrerelease = "dev"
-
-	VersionMetadata = ""
+	VersionPrerelease string
+	// VersionMetadata may be added to give more non-normalised information on a build
+	// like a commit SHA for example.
+	//
+	// Ex: 1.0.0-dev+metadata
+	VersionMetadata string
 )
 
 var PackerVersion *pluginVersion.PluginVersion
@@ -45,8 +52,21 @@ func FormattedVersion() string {
 var SemVer *version.Version
 
 func init() {
-	PackerVersion = pluginVersion.InitializePluginVersion(Version, VersionPrerelease)
-	SemVer = PackerVersion.SemVer()
+	var err error
+
+	// Note: we use strings.TrimSpace on the version read from version/VERSION
+	// as it could have trailing whitespaces that must not be part of the
+	// version string, otherwise version.NewSemver will reject it.
+	SemVer, err = version.NewSemver(strings.TrimSpace(rawVersion))
+	if err != nil {
+		panic(fmt.Sprintf("Invalid semver version specified in 'version/VERSION' (%q): %s", rawVersion, err))
+	}
+
+	Version = SemVer.Core().String()
+	VersionPrerelease = SemVer.Prerelease()
+	VersionMetadata = SemVer.Metadata()
+
+	PackerVersion = pluginVersion.InitializePluginVersion(SemVer.Core().String(), SemVer.Prerelease())
 }
 
 // String returns the complete version string, including prerelease