version: limit core version to 3 segments

The go-version library we use for parsing versions from the plugin
supports 4-segmented versions.
This may not be ideal for us, as we want to limit the sprawling nature
of plugin installations, which if we start accepting sub-patch version
bumps, may become quite strange.
The release workflows we offer as template does not take that into
account, and I'm not sure our docs do as well.

Since there are many unknowns here, 4-segmented version numbers are not
semver-valid, and we do not know how tooling will react, we ultimately
decide not to allow those in the SDK.

If a developer tries to define a 4-segmented version number, the plugin
will crash instantly, at least giving users a message quickly that the
version number is invalid, and that they need to limit themselves to a
3-segment version number.

version/version.go

@@ -47,6 +47,11 @@ func InitializePluginVersion(vers, versionPrerelease string) *PluginVersion {
 // As NewRawVersion, if the version is invalid, it will panic.
 func NewRawVersion(rawSemVer string) *PluginVersion {
 	vers := version.Must(version.NewVersion(rawSemVer))
+
+	if len(vers.Segments()) != 3 {
+		panic(fmt.Sprintf("versions should only have 3 segments, %q had %d", rawSemVer, len(vers.Segments())))
+	}
+
 	return &PluginVersion{
 		version:           vers.Core().String(),
 		versionPrerelease: vers.Prerelease(),
@@ -81,16 +86,7 @@ func NewPluginVersion(vers, versionPrerelease, versionMetadata string) *PluginVe
 		versionRawString = fmt.Sprintf("%s+%s", versionRawString, versionMetadata)
 	}
 
-	// This call initializes the SemVer to make sure that if Packer crashes due
-	// to an invalid SemVer it's at the very beginning of the Packer run.
-	semVer := version.Must(version.NewVersion(versionRawString))
-
-	return &PluginVersion{
-		version:           semVer.Core().String(),
-		versionPrerelease: semVer.Prerelease(),
-		versionMetadata:   semVer.Metadata(),
-		semVer:            semVer,
-	}
+	return NewRawVersion(versionRawString)
 }
 
 type PluginVersion struct {

version/version_test.go

@@ -62,6 +62,14 @@ func Test_PluginVersionCreate(t *testing.T) {
 			true,
 			"",
 		},
+		{
+			"4-parts version, should not be accepted",
+			"1.1.1.1",
+			"",
+			"",
+			true,
+			"",
+		},
 	}
 
 	for _, tt := range tests {