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feat: implement idiomatic error handling with As function (#14)
Signed-off-by: Yordis Prieto <yordis.prieto@gmail.com>
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‎error.go‎

Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -894,6 +894,35 @@ func addHelpLink(e *TrogonError, description, url string) {
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})
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}
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type trogonError interface {
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Is(error) bool
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}
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// As checks if the error matches the target and returns the TrogonError if it does.
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// This combines error matching and error extraction in a single, more idiomatic operation.
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// The target can be either a TrogonError or an ErrorTemplate.
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// Returns the TrogonError and true if the error matches, nil and false otherwise.
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//
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// Example usage:
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//
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// if trogonErr, ok := trogonerror.As(err, users.ErrUserNotFound); ok {
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// return trogonErr.WithChanges(
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// trogonerror.WithChangeMetadataValue(trogonerror.VisibilityPublic, "user_id", req.UserID),
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// )
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// }
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func As(err error, target trogonError) (*TrogonError, bool) {
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var trogonErr *TrogonError
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if !errors.As(err, &trogonErr) {
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return nil, false
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}
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if !target.Is(trogonErr) {
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return nil, false
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}
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return trogonErr, true
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}
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func addMetadataValue(e *TrogonError, visibility Visibility, key, value string) {
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if len(e.metadata) == 0 {
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e.metadata = make(Metadata)

‎error_test.go‎

Lines changed: 132 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -785,6 +785,138 @@ func (c CustomError) Error() string {
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return c.msg
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}
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788+
func TestAs(t *testing.T) {
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t.Run("As returns TrogonError when error matches", func(t *testing.T) {
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template := trogonerror.NewErrorTemplate("shopify.inventory", "INSUFFICIENT_INVENTORY",
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trogonerror.TemplateWithCode(trogonerror.CodeFailedPrecondition))
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originalErr := template.NewError(
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trogonerror.WithMetadataValue(trogonerror.VisibilityPublic, "productId", "gid://shopify/Product/1234567890"))
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trogonErr, ok := trogonerror.As(originalErr, template)
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assert.True(t, ok)
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assert.NotNil(t, trogonErr)
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assert.Equal(t, "shopify.inventory", trogonErr.Domain())
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assert.Equal(t, "INSUFFICIENT_INVENTORY", trogonErr.Reason())
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assert.Equal(t, "gid://shopify/Product/1234567890", trogonErr.Metadata()["productId"].Value())
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})
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t.Run("As returns false when error doesn't match", func(t *testing.T) {
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template1 := trogonerror.NewErrorTemplate("shopify.inventory", "INSUFFICIENT_INVENTORY")
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template2 := trogonerror.NewErrorTemplate("shopify.users", "NOT_FOUND")
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err1 := template1.NewError()
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trogonErr, ok := trogonerror.As(err1, template2)
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assert.False(t, ok)
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assert.Nil(t, trogonErr)
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})
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t.Run("As returns false for non-TrogonError", func(t *testing.T) {
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template := trogonerror.NewErrorTemplate("shopify.inventory", "INSUFFICIENT_INVENTORY")
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regularErr := errors.New("regular error")
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trogonErr, ok := trogonerror.As(regularErr, template)
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assert.False(t, ok)
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assert.Nil(t, trogonErr)
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})
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t.Run("As works with WithChanges pattern", func(t *testing.T) {
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template := trogonerror.NewErrorTemplate("shopify.inventory", "INSUFFICIENT_INVENTORY",
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trogonerror.TemplateWithCode(trogonerror.CodeResourceExhausted))
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originalErr := template.NewError(
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trogonerror.WithMetadataValue(trogonerror.VisibilityPublic, "productId", "gid://shopify/Product/1234567890"))
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trogonErr, ok := trogonerror.As(originalErr, template)
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assert.True(t, ok)
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assert.NotNil(t, trogonErr)
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modifiedErr := trogonErr.WithChanges(
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trogonerror.WithChangeMetadataValue(trogonerror.VisibilityPublic, "main_order_id", "order_123"),
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trogonerror.WithChangeMetadataValue(trogonerror.VisibilityPublic, "listing_count", "5"),
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)
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assert.Equal(t, "order_123", modifiedErr.Metadata()["main_order_id"].Value())
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assert.Equal(t, "5", modifiedErr.Metadata()["listing_count"].Value())
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assert.Equal(t, "gid://shopify/Product/1234567890", modifiedErr.Metadata()["productId"].Value()) // Original preserved
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})
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846+
t.Run("As works with TrogonError directly", func(t *testing.T) {
847+
originalErr := trogonerror.NewError("shopify.inventory", "INSUFFICIENT_INVENTORY",
848+
trogonerror.WithCode(trogonerror.CodeFailedPrecondition),
849+
trogonerror.WithMetadataValue(trogonerror.VisibilityPublic, "productId", "gid://shopify/Product/1234567890"))
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851+
// Test with TrogonError as target (not template)
852+
trogonErr, ok := trogonerror.As(originalErr, originalErr)
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assert.True(t, ok)
854+
assert.NotNil(t, trogonErr)
855+
assert.Equal(t, "shopify.inventory", trogonErr.Domain())
856+
assert.Equal(t, "INSUFFICIENT_INVENTORY", trogonErr.Reason())
857+
})
858+
859+
t.Run("As works with wrapped TrogonError", func(t *testing.T) {
860+
template := trogonerror.NewErrorTemplate("shopify.inventory", "INSUFFICIENT_INVENTORY")
861+
862+
originalErr := template.NewError(
863+
trogonerror.WithMetadataValue(trogonerror.VisibilityPublic, "productId", "gid://shopify/Product/1234567890"))
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865+
// Wrap the TrogonError with fmt.Errorf (this was the problematic scenario)
866+
wrappedErr := fmt.Errorf("context: %w", originalErr)
867+
868+
// Test the As function with the wrapped error
869+
trogonErr, ok := trogonerror.As(wrappedErr, template)
870+
assert.True(t, ok, "As should return true for wrapped TrogonError")
871+
assert.NotNil(t, trogonErr, "As should return non-nil TrogonError")
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873+
// Verify the extracted error has the correct properties
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assert.Equal(t, "shopify.inventory", trogonErr.Domain())
875+
assert.Equal(t, "INSUFFICIENT_INVENTORY", trogonErr.Reason())
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assert.Equal(t, "gid://shopify/Product/1234567890", trogonErr.Metadata()["productId"].Value())
877+
})
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879+
}
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func TestInternalMethods(t *testing.T) {
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t.Run("TrogonError.is method delegates to Is", func(t *testing.T) {
883+
err1 := trogonerror.NewError("shopify.session", "SESSION_EXPIRED")
884+
err2 := trogonerror.NewError("shopify.session", "SESSION_EXPIRED")
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err3 := trogonerror.NewError("shopify.session", "SESSION_INVALID")
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// Test the internal is method by using it in the As function
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// This indirectly tests the is method since As calls target.is(err)
889+
trogonErr, ok := trogonerror.As(err2, err1)
890+
assert.True(t, ok)
891+
assert.NotNil(t, trogonErr)
892+
893+
trogonErr2, ok2 := trogonerror.As(err3, err1)
894+
assert.False(t, ok2)
895+
assert.Nil(t, trogonErr2)
896+
})
897+
898+
t.Run("ErrorTemplate.is method delegates to Is", func(t *testing.T) {
899+
template := trogonerror.NewErrorTemplate("shopify.session", "SESSION_EXPIRED")
900+
err1 := template.NewError()
901+
err2 := trogonerror.NewError("shopify.session", "SESSION_EXPIRED")
902+
err3 := trogonerror.NewError("shopify.session", "SESSION_INVALID")
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904+
// Test the internal is method by using it in the As function
905+
// This indirectly tests the is method since As calls target.is(err)
906+
trogonErr, ok := trogonerror.As(err1, template)
907+
assert.True(t, ok)
908+
assert.NotNil(t, trogonErr)
909+
910+
trogonErr2, ok2 := trogonerror.As(err2, template)
911+
assert.True(t, ok2)
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assert.NotNil(t, trogonErr2)
913+
914+
trogonErr3, ok3 := trogonerror.As(err3, template)
915+
assert.False(t, ok3)
916+
assert.Nil(t, trogonErr3)
917+
})
918+
}
919+
788920
func TestErrorTemplate(t *testing.T) {
789921
t.Run("NewErrorTemplate creates template with defaults", func(t *testing.T) {
790922
template := trogonerror.NewErrorTemplate("shopify.session", "SESSION_EXPIRED")

‎example_test.go‎

Lines changed: 34 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -376,3 +376,37 @@ func ExampleWithMetadataValuef_formattedValues() {
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// Amount: $299.99
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// Request ID: req_1234567890_5432109876
378378
}
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func ExampleAs_idiomaticErrorHandling() {
381+
// Define error templates (typically done at package level)
382+
var ErrInsufficientStock = trogonerror.NewErrorTemplate("inventory", "INSUFFICIENT_STOCK",
383+
trogonerror.TemplateWithCode(trogonerror.CodeResourceExhausted))
384+
385+
// Simulate an error from inventory service
386+
inventoryErr := ErrInsufficientStock.NewError(
387+
trogonerror.WithMetadataValue(trogonerror.VisibilityPublic, "product_id", "prod_12345"))
388+
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// Old verbose pattern:
390+
// if inventory.ErrInsufficientStock.Is(err) {
391+
// var trogonErr *trogonerror.TrogonError
392+
// if errors.As(err, &trogonErr) {
393+
// return nil, trogonErr.WithChanges(...)
394+
// }
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// }
396+
397+
// New idiomatic pattern using As:
398+
if trogonErr, ok := trogonerror.As(inventoryErr, ErrInsufficientStock); ok {
399+
modifiedErr := trogonErr.WithChanges(
400+
trogonerror.WithChangeMetadataValue(trogonerror.VisibilityPublic, "order_id", "order_789"),
401+
trogonerror.WithChangeMetadataValue(trogonerror.VisibilityPublic, "requested_quantity", "10"),
402+
)
403+
fmt.Printf("Modified error domain: %s\n", modifiedErr.Domain())
404+
fmt.Printf("Order ID: %s\n", modifiedErr.Metadata()["order_id"].Value())
405+
fmt.Printf("Requested quantity: %s\n", modifiedErr.Metadata()["requested_quantity"].Value())
406+
}
407+
408+
// Output:
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// Modified error domain: inventory
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// Order ID: order_789
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// Requested quantity: 10
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}

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