chore/Scrutinize pyproject for backends (#234)

* Add VerifySpecfile

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

internal/api/types.go

@@ -172,6 +172,9 @@ type LanguageBackend struct {
 	// This field is mandatory.
 	Specfile string
 
+	// An optional function to analyze the specfile to determine compatibility
+	IsSpecfileCompatible func(fullPath string) (bool, error)
+
 	// The filename of the lockfile, e.g. "poetry.lock" for
 	// Poetry.
 	Lockfile string

internal/backends/backends.go

@@ -101,12 +101,33 @@ func GetBackend(ctx context.Context, language string) api.LanguageBackend {
 	for _, b := range backends {
 		if util.Exists(b.Specfile) &&
 			util.Exists(b.Lockfile) {
+			if b.IsSpecfileCompatible != nil {
+				isValid, err := b.IsSpecfileCompatible(b.Specfile)
+				if err != nil {
+					panic(err)
+				}
+				if !isValid {
+					continue
+				}
+			}
 			return b
 		}
 	}
 	for _, b := range backends {
-		if util.Exists(b.Specfile) ||
-			util.Exists(b.Lockfile) {
+		if util.Exists(b.Specfile) {
+			if b.IsSpecfileCompatible != nil {
+				isValid, err := b.IsSpecfileCompatible(b.Specfile)
+				if err != nil {
+					panic(err)
+				}
+				if !isValid {
+					continue
+				}
+			}
+
+			return b
+		}
+		if util.Exists(b.Lockfile) {
 			return b
 		}
 	}

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 {