Gate the poetry backend on whether we find a poetry section in it

internal/backends/python/python.go

@@ -55,7 +55,7 @@ type pyprojectPackageCfg struct {
 // file.
 type pyprojectTOML struct {
 	Tool struct {
-		Poetry struct {
+		Poetry *struct {
 			Name string `json:"name"`
 			// interface{} because they can be either
 			// strings or maps (why?? good lord).
@@ -266,12 +266,13 @@ func searchPypi(query string) []api.PkgInfo {
 // (either a full path or just a name like "python3") to use when invoking Python.
 func makePythonPoetryBackend(python string) api.LanguageBackend {
 	return api.LanguageBackend{
-		Name:             "python3-poetry",
-		Alias:            "python-python3-poetry",
-		Specfile:         "pyproject.toml",
-		Lockfile:         "poetry.lock",
-		IsAvailable:      poetryIsAvailable,
-		FilenamePatterns: []string{"*.py"},
+		Name:                 "python3-poetry",
+		Alias:                "python-python3-poetry",
+		Specfile:             "pyproject.toml",
+		IsSpecfileCompatible: verifyPoetrySpecfile,
+		Lockfile:             "poetry.lock",
+		IsAvailable:          poetryIsAvailable,
+		FilenamePatterns:     []string{"*.py"},
 		Quirks: api.QuirksAddRemoveAlsoLocks |
 			api.QuirksAddRemoveAlsoInstalls,
 		NormalizePackageArgs: normalizePackageArgs,
@@ -567,6 +568,15 @@ func readPyproject() (*pyprojectTOML, error) {
 	return &cfg, nil
 }
 
+func verifyPoetrySpecfile(path string) (bool, error) {
+	cfg, err := readPyproject()
+	if err != nil {
+		return false, err
+	}
+
+	return cfg.Tool.Poetry != nil, nil
+}
+
 func listPoetrySpecfile() (map[api.PkgName]api.PkgSpec, error) {
 	cfg, err := readPyproject()
 	if err != nil {