cm: verify dependencies

Package cm should only depend on structs and unsafe.

Author: ydnar

cm/case.go

@@ -1,7 +1,5 @@
 package cm
 
-import "errors"
-
 // CaseUnmarshaler returns an function that can unmarshal text into
 // [variant] or [enum] case T.
 //
@@ -46,6 +44,14 @@ func CaseUnmarshaler[T ~uint8 | ~uint16 | ~uint32](cases []string) func(v *T, te
 const linearScanThreshold = 16
 
 var (
-	errEmpty          = errors.New("empty text")
-	errNoMatchingCase = errors.New("no matching case")
+	errEmpty          = &stringError{"empty text"}
+	errNoMatchingCase = &stringError{"no matching case"}
 )
+
+type stringError struct {
+	err string
+}
+
+func (err *stringError) Error() string {
+	return err.err
+}

cm/dependencies_test.go

@@ -1,4 +1,4 @@
-//go:build !wasm
+//go:build !wasip1 && !wasip2 && !tinygo
 
 package cm
 
@@ -15,11 +15,12 @@ func TestDependencies(t *testing.T) {
 	cmd.Stdout = stdout
 	err := cmd.Run()
 	if err != nil {
-		t.Fatal(err)
+		t.Error(err)
+		return
 	}
 
 	got := strings.TrimSpace(stdout.String())
-	const want = "[errors structs unsafe]" // Should not include "encoding/json"
+	const want = "[structs unsafe]" // Should not include "encoding/json"
 	if got != want {
 		t.Errorf("Expected dependencies %s, got %s", want, got)
 	}