add allow-unresolved-version go-proxy config option (#8)

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

README.md

@@ -205,9 +205,10 @@ The `version.want` option allows a special entry:
 
 The `go-proxy` version method reaches out to `proxy.golang.org` to determine the latest version of a Go module. It requires the following configuration options:
 
-| Option | Description                                                                                      |
-|--------|--------------------------------------------------------------------------------------------------|
-| `module` | The FQDN to the Go module (e.g. `github.com/anchore/syft`)                  |
+| Option | Description                                                                                                          |
+|--------|----------------------------------------------------------------------------------------------------------------------|
+| `module` | The FQDN to the Go module (e.g. `github.com/anchore/syft`)                                                           |
+| `allow-unresolved-version` | If the latest version cannot be found by the proxy allow for "latest" as a valid value (which `go install` supports) | 
 
 The `version.want` option allows a special entry:
 - `latest`: don't pin to a version, use the latest available

tool/goproxy/version_resolver.go

@@ -11,6 +11,8 @@ import (
 	"github.com/anchore/binny/internal/log"
 )
 
+const latest = "latest"
+
 var _ binny.VersionResolver = (*VersionResolver)(nil)
 
 type VersionResolver struct {
@@ -19,7 +21,8 @@ type VersionResolver struct {
 }
 
 type VersionResolutionParameters struct {
-	Module string `json:"module" yaml:"module" mapstructure:"module"`
+	Module                 string `json:"module" yaml:"module" mapstructure:"module"`
+	AllowUnresolvedVersion bool   `json:"allow-unresolved-version" yaml:"allow-unresolved-version" mapstructure:"allow-unresolved-version"`
 }
 
 func NewVersionResolver(cfg VersionResolutionParameters) *VersionResolver {
@@ -35,7 +38,7 @@ func (v VersionResolver) ResolveVersion(want, _ string) (string, error) {
 		return want, nil
 	}
 
-	if want == "latest" {
+	if want == latest {
 		return v.findLatestVersion("")
 	}
 
@@ -45,7 +48,7 @@ func (v VersionResolver) ResolveVersion(want, _ string) (string, error) {
 }
 
 func (v VersionResolver) UpdateVersion(want, constraint string) (string, error) {
-	if want == "latest" {
+	if want == latest {
 		if constraint != "" {
 			return "", fmt.Errorf("cannot specify a version constraint with 'latest' go module version")
 		}
@@ -75,8 +78,21 @@ func (v VersionResolver) findLatestVersion(versionConstraint string) (string, er
 		return "", fmt.Errorf("failed to filter latest version: %v", err)
 	}
 
-	log.WithFields("latest", latestVersion, "module", v.config.Module).
-		Trace("found latest version from the go proxy")
+	if latestVersion != "" {
+		log.WithFields(latest, latestVersion, "module", v.config.Module).
+			Trace("found latest version from the go proxy")
+	} else {
+		log.WithFields("module", v.config.Module).Trace("could not resolve latest version from go proxy")
+	}
+
+	if latestVersion == "" {
+		if v.config.AllowUnresolvedVersion {
+			// this can happen if the source repo has no tags, the proxy then won't know about it.
+			log.WithFields("module", v.config.Module).Trace("using 'latest' as the version")
+			return latest, nil
+		}
+		return "", fmt.Errorf("could not resolve latest version for module %q", v.config.Module)
+	}
 
 	return latestVersion, nil
 }

tool/goproxy/version_resolver_test.go

@@ -44,6 +44,29 @@ func TestVersionResolver_ResolveVersion(t *testing.T) {
 			version: "bogus",
 			want:    "bogus",
 		},
+		{
+			name: "do not allow for unresolved versions",
+			config: VersionResolutionParameters{
+				Module: "github.com/anchore/binny",
+			},
+			version: "latest",
+			wantErr: require.Error,
+			availableVersionsFetcher: func(url string) ([]string, error) {
+				return []string{""}, nil
+			},
+		},
+		{
+			name: "allow for unresolved versions",
+			config: VersionResolutionParameters{
+				Module:                 "github.com/anchore/binny",
+				AllowUnresolvedVersion: true,
+			},
+			version: "latest",
+			want:    "latest", // this is a pass through to go-install, which supports this as input
+			availableVersionsFetcher: func(url string) ([]string, error) {
+				return []string{""}, nil
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {