fix(checkers): load custom YAML checkers from disk, not embedded FS (#230)

`LoadCustomYamlCheckers(dir)` walks `os.DirFS(dir)` to find YAML files
on local disk, but the closure it used read file content via
`builtinCheckers.ReadFile(path)` — i.e. always the embedded FS. For
every custom YAML file, `ReadFile` returned `fs.ErrNotExist`, the error
was silently swallowed by the top-level error check in the walk
callback, and the checker was never loaded.

Net result: `globstar check --checkers=local` in a repo with a
`.globstar/*.yml` found zero issues regardless of the YAML's content,
while the same YAML loaded via `--checkers=builtin` worked fine —
confirming the loader (not the YAML) was the problem.

Fix: thread a per-backend `readFile func(string) ([]byte, error)`
through `findYamlCheckers`. `LoadBuiltinYamlCheckers` passes
`builtinCheckers.ReadFile`; `LoadCustomYamlCheckers` passes a closure
that reads from disk via `os.ReadFile(filepath.Join(dir, p))`. No
public API breakage.

Add a regression test that writes a YAML checker to a temp dir and
asserts `LoadCustomYamlCheckers` returns it.

Co-authored-by: Sanket Saurav <sanketsaurav@gmail.com>

Author: sanket-deepsource

checkers/checker.go

@@ -13,7 +13,7 @@ import (
 //go:embed **/*.y*ml
 var builtinCheckers embed.FS
 
-func findYamlCheckers(checkersMap map[analysis.Language][]analysis.Analyzer) func(path string, d fs.DirEntry, err error) error {
+func findYamlCheckers(checkersMap map[analysis.Language][]analysis.Analyzer, readFile func(string) ([]byte, error)) func(path string, d fs.DirEntry, err error) error {
 	return func(path string, d fs.DirEntry, err error) error {
 		if err != nil {
 			return nil
@@ -29,7 +29,7 @@ func findYamlCheckers(checkersMap map[analysis.Language][]analysis.Analyzer) fun
 			return nil
 		}
 
-		fileContent, err := builtinCheckers.ReadFile(path)
+		fileContent, err := readFile(path)
 		if err != nil {
 			return nil
 		}
@@ -47,13 +47,15 @@ func findYamlCheckers(checkersMap map[analysis.Language][]analysis.Analyzer) fun
 
 func LoadBuiltinYamlCheckers() (map[analysis.Language][]analysis.Analyzer, error) {
 	checkersMap := make(map[analysis.Language][]analysis.Analyzer)
-	err := fs.WalkDir(builtinCheckers, ".", findYamlCheckers(checkersMap))
+	err := fs.WalkDir(builtinCheckers, ".", findYamlCheckers(checkersMap, builtinCheckers.ReadFile))
 	return checkersMap, err
 }
 
 func LoadCustomYamlCheckers(dir string) (map[analysis.Language][]analysis.Analyzer, error) {
 	checkersMap := make(map[analysis.Language][]analysis.Analyzer)
-	err := fs.WalkDir(os.DirFS(dir), ".", findYamlCheckers(checkersMap))
+	err := fs.WalkDir(os.DirFS(dir), ".", findYamlCheckers(checkersMap, func(p string) ([]byte, error) {
+		return os.ReadFile(filepath.Join(dir, p))
+	}))
 	return checkersMap, err
 }
 

checkers/checker_test.go

@@ -0,0 +1,52 @@
+package checkers
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"globstar.dev/analysis"
+)
+
+// TestLoadCustomYamlCheckers_ReadsFromDisk is a regression test ensuring that
+// custom YAML checkers are loaded from the local filesystem and not silently
+// dropped because the loader was reading from the embedded FS.
+func TestLoadCustomYamlCheckers_ReadsFromDisk(t *testing.T) {
+	dir := t.TempDir()
+	const yml = `language: go
+name: go_custom_test
+message: "custom checker fired"
+category: security
+severity: critical
+pattern: >
+  [
+    (import_spec
+      path: (interpreted_string_literal) @import
+      (#eq? @import "\"crypto/md5\""))
+  ] @go_custom_test
+`
+	if err := os.WriteFile(filepath.Join(dir, "custom.yml"), []byte(yml), 0o644); err != nil {
+		t.Fatalf("write yaml: %v", err)
+	}
+
+	checkersMap, err := LoadCustomYamlCheckers(dir)
+	if err != nil {
+		t.Fatalf("LoadCustomYamlCheckers: %v", err)
+	}
+
+	goCheckers, ok := checkersMap[analysis.LangGo]
+	if !ok || len(goCheckers) == 0 {
+		t.Fatalf("expected at least one Go checker loaded from disk, got map=%v", checkersMap)
+	}
+
+	found := false
+	for _, c := range goCheckers {
+		if c.Name == "go_custom_test" {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatalf("expected 'go_custom_test' to be loaded; got %+v", goCheckers)
+	}
+}