fix(go): Handle more cursor pagination stopping conditions (#5759)

fern/pages/changelogs/go-sdk/2025-01-26.mdx

@@ -0,0 +1,3 @@
+## 0.36.2
+**`(fix):`** Fix cursor pagination stopping condition when the cursor types do not match (e.g. a `*string` cursor type with a `string` next cursor type).
+

generators/go/internal/generator/generator.go

@@ -580,6 +580,7 @@ func (g *Generator) generate(ir *fernir.IntermediateRepresentation, mode Mode) (
 		if generatedPagination {
 			files = append(files, newPageFile(g.coordinator))
 			files = append(files, newPagerFile(g.coordinator, g.config.ImportPath))
+			files = append(files, newPagerTestFile(g.coordinator))
 		}
 		clientTestFile, err := newClientTestFile(g.config.ImportPath, rootPackageName, g.coordinator, g.config.PackageLayout, g.config.ClientName, g.config.ClientConstructorName)
 		if err != nil {
@@ -1289,6 +1290,14 @@ func newPagerFile(coordinator *coordinator.Client, baseImportPath string) *File
 	)
 }
 
+func newPagerTestFile(coordinator *coordinator.Client) *File {
+	return NewFile(
+		coordinator,
+		"internal/pager_test.go",
+		[]byte(pagerTestFile),
+	)
+}
+
 func newPageFile(coordinator *coordinator.Client) *File {
 	return NewFile(
 		coordinator,

generators/go/internal/generator/sdk.go

@@ -68,6 +68,9 @@ var (
 	//go:embed sdk/internal/pager.go
 	pagerFile string
 
+	//go:embed sdk/internal/pager_test.go
+	pagerTestFile string
+
 	//go:embed sdk/utils/pointer.go
 	pointerFile string
 
@@ -1360,6 +1363,7 @@ func (f *fileWriter) WriteClient(
 				pagerConstructor = "internal.NewCursorPager"
 
 				f.P("readPageResponse := func(response ", endpoint.ResponseType, ") *internal.PageResponse[", endpoint.PaginationInfo.PageGoType, ",", endpoint.PaginationInfo.ResultsSingleGoType, "] {")
+				f.P("var zeroValue ", endpoint.PaginationInfo.NextCursorGoType)
 				if len(endpoint.PaginationInfo.NextCursor.PropertyPath) > 0 {
 					f.P("var next ", endpoint.PaginationInfo.NextCursorGoType)
 					f.P(endpoint.PaginationInfo.NextCursorNilCheck)
@@ -1381,6 +1385,7 @@ func (f *fileWriter) WriteClient(
 					f.P("if next == nil {")
 					f.P("return &internal.PageResponse[", endpoint.PaginationInfo.PageGoType, ",", endpoint.PaginationInfo.ResultsSingleGoType, "]{")
 					f.P("Results: results,")
+					f.P("Done: next == zeroValue,")
 					f.P("}")
 					f.P("}")
 				}
@@ -1396,6 +1401,7 @@ func (f *fileWriter) WriteClient(
 					f.P("Next: next,")
 				}
 				f.P("Results: results,")
+				f.P("Done: next == zeroValue,")
 				f.P("}")
 				f.P("}")
 			case "offset":

generators/go/internal/generator/sdk/internal/pager.go

@@ -39,6 +39,7 @@ type PageRequest[Cursor comparable] struct {
 type PageResponse[Cursor comparable, Result any] struct {
 	Results []Result
 	Next    Cursor
+	Done    bool
 }
 
 // PageRequestFunc prepares the *CallParams from the given page request.
@@ -117,8 +118,7 @@ func (p *Pager[
 	return &core.Page[Results]{
 		Results: pageResponse.Results,
 		NextPageFunc: func(ctx context.Context) (*core.Page[Results], error) {
-			var next Cursor
-			if pageResponse.Next == next {
+			if pageResponse.Done {
 				return nil, core.ErrNoPages
 			}
 			return p.GetPage(ctx, pageResponse.Next)

generators/go/internal/generator/sdk/internal/pager_test.go

@@ -0,0 +1,162 @@
+package internal
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type TestPageResponse struct {
+	Items []TestPageItem `json:"items"`
+	Next  string         `json:"next"`
+}
+
+type TestPageItem struct {
+	ID   string `json:"id"`
+	Name string `json:"name"`
+}
+
+func TestPager(t *testing.T) {
+	tests := []struct {
+		description string
+		givePages   []TestPageResponse
+		giveCursor  string
+		wantItems   []TestPageItem
+		wantError   error
+	}{
+		{
+			description: "handles multiple pages successfully",
+			givePages: []TestPageResponse{
+				{
+					Items: []TestPageItem{{ID: "1", Name: "First"}},
+					Next:  "abc",
+				},
+				{
+					Items: []TestPageItem{{ID: "2", Name: "Second"}},
+					Next:  "def",
+				},
+				{
+					Items: []TestPageItem{{ID: "3", Name: "Third"}},
+					Next:  "",
+				},
+			},
+			wantItems: []TestPageItem{
+				{ID: "1", Name: "First"},
+				{ID: "2", Name: "Second"},
+				{ID: "3", Name: "Third"},
+			},
+		},
+		{
+			description: "handles empty response",
+			givePages: []TestPageResponse{
+				{
+					Items: []TestPageItem{},
+					Next:  "",
+				},
+			},
+			wantItems: nil,
+		},
+		{
+			description: "handles single page",
+			givePages: []TestPageResponse{
+				{
+					Items: []TestPageItem{{ID: "1", Name: "Only"}},
+					Next:  "",
+				},
+			},
+			wantItems: []TestPageItem{
+				{ID: "1", Name: "Only"},
+			},
+		},
+		{
+			description: "handles initial cursor",
+			giveCursor:  "abc",
+			givePages: []TestPageResponse{
+				{
+					Items: []TestPageItem{{ID: "1", Name: "First"}},
+					Next:  "",
+				},
+			},
+			wantItems: []TestPageItem{
+				{ID: "1", Name: "First"},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.description, func(t *testing.T) {
+			var pageIndex int
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if pageIndex >= len(tt.givePages) {
+					t.Fatal("requested more pages than available")
+				}
+				if pageIndex > 0 {
+					assert.Equal(t, tt.givePages[pageIndex-1].Next, r.URL.Query().Get("cursor"))
+				}
+				require.NoError(t, json.NewEncoder(w).Encode(tt.givePages[pageIndex]))
+				pageIndex++
+			}))
+			defer server.Close()
+
+			caller := NewCaller(
+				&CallerParams{
+					Client: server.Client(),
+				},
+			)
+			pager := NewCursorPager(
+				caller,
+				func(request *PageRequest[*string]) *CallParams {
+					url := server.URL
+					if request.Cursor != nil {
+						url += "?cursor=" + *request.Cursor
+					}
+					return &CallParams{
+						URL:      url,
+						Method:   http.MethodGet,
+						Response: request.Response,
+					}
+				},
+				func(response *TestPageResponse) *PageResponse[*string, *TestPageItem] {
+					var items []*TestPageItem
+					for _, item := range response.Items {
+						itemCopy := item
+						items = append(items, &itemCopy)
+					}
+					var next *string
+					if response.Next != "" {
+						next = &response.Next
+					}
+					return &PageResponse[*string, *TestPageItem]{
+						Results: items,
+						Next:    next,
+						Done:    response.Next == "",
+					}
+				},
+			)
+
+			page, err := pager.GetPage(context.Background(), &tt.giveCursor)
+			if tt.wantError != nil {
+				assert.Equal(t, tt.wantError, err)
+				return
+			}
+			require.NoError(t, err)
+
+			var items []TestPageItem
+			iter := page.Iterator()
+			for iter.Next(context.Background()) {
+				item := iter.Current()
+				items = append(items, TestPageItem{
+					ID:   item.ID,
+					Name: item.Name,
+				})
+			}
+			require.NoError(t, iter.Err())
+			assert.Equal(t, tt.wantItems, items)
+		})
+	}
+}

generators/go/sdk/versions.yml

@@ -1,3 +1,10 @@
+- version: 0.36.2
+  changelogEntry:
+    - type: fix
+      summary: >-
+        Fix cursor pagination stopping condition when the cursor types do not
+        match (e.g. a `*string` cursor type with a `string` next cursor type).
+  irVersion: 53
 - version: 0.36.1
   changelogEntry:
     - type: fix

packages/cli/fern-definition/ir-to-jsonschema/src/__test__/__snapshots__/pagination/type_users_ListUsersMixedTypePaginationResponse.json

@@ -0,0 +1,37 @@
+{
+  "type": "object",
+  "properties": {
+    "next": {
+      "type": "string"
+    },
+    "data": {
+      "type": "array",
+      "items": {
+        "$ref": "#/definitions/users.User"
+      }
+    }
+  },
+  "required": [
+    "next",
+    "data"
+  ],
+  "additionalProperties": false,
+  "definitions": {
+    "users.User": {
+      "type": "object",
+      "properties": {
+        "name": {
+          "type": "string"
+        },
+        "id": {
+          "type": "integer"
+        }
+      },
+      "required": [
+        "name",
+        "id"
+      ],
+      "additionalProperties": false
+    }
+  }
+}