fix(go): allow the use of snake case fields in dotprompt templates (#3744)

Author: hugoaguirre

go/ai/prompt.go

@@ -16,6 +16,7 @@ package ai
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"log/slog"
@@ -260,7 +261,16 @@ func buildVariables(variables any) (map[string]any, error) {
 
 	v := reflect.Indirect(reflect.ValueOf(variables))
 	if v.Kind() == reflect.Map {
-		return variables.(map[string]any), nil
+		// ensure JSON tags are taken in consideration (allowing snake case fields)
+		jsonData, err := json.Marshal(variables)
+		if err != nil {
+			return nil, fmt.Errorf("unable to marshal prompt field values: %w", err)
+		}
+		var resultVariables map[string]any
+		if err := json.Unmarshal(jsonData, &resultVariables); err != nil {
+			return nil, fmt.Errorf("unable to unmarshal prompt field values: %w", err)
+		}
+		return resultVariables, nil
 	}
 	if v.Kind() != reflect.Struct {
 		return nil, errors.New("prompt.buildVariables: fields not a struct or pointer to a struct or a map")

go/ai/prompt_test.go

@@ -904,7 +904,7 @@ output:
 ---
 Hello, {{name}}!
 `
-	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0644)
+	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create mock prompt file: %v", err)
 	}
@@ -941,6 +941,71 @@ Hello, {{name}}!
 	}
 }
 
+func TestLoadPromptSnakeCase(t *testing.T) {
+	tempDir := t.TempDir()
+	mockPromptFile := filepath.Join(tempDir, "snake.prompt")
+	mockPromptContent := `---
+model: googleai/gemini-2.5-flash
+input:
+  schema:
+    items(array):
+      teamColor: string
+      team_name: string
+---
+{{#each items as |it|}}
+{{ it.teamColor }},{{ it.team_name }}
+{{/each}}
+`
+	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0o644)
+	if err != nil {
+		t.Fatalf("Failed to create mock prompt file: %v", err)
+	}
+
+	reg := registry.New()
+	LoadPrompt(reg, tempDir, "snake.prompt", "snake-namespace")
+
+	prompt := LookupPrompt(reg, "snake-namespace/snake")
+	if prompt == nil {
+		t.Fatalf("prompt was not registered")
+	}
+
+	type SnakeInput struct {
+		TeamColor string `json:"teamColor"` // intentionally leaving camel case to test snake + camel support
+		TeamName  string `json:"team_name"`
+	}
+
+	input := map[string]any{"items": []SnakeInput{
+		{TeamColor: "RED", TeamName: "Firebase"},
+		{TeamColor: "BLUE", TeamName: "Gophers"},
+		{TeamColor: "GREEN", TeamName: "Google"},
+	}}
+
+	actionOpts, err := prompt.Render(context.Background(), input)
+	if err != nil {
+		t.Fatalf("error rendering prompt: %v", err)
+	}
+	if actionOpts.Messages == nil {
+		t.Fatal("expecting messages to be rendered")
+	}
+	renderedPrompt := actionOpts.Messages[0].Text()
+	for line := range strings.SplitSeq(renderedPrompt, "\n") {
+		trimmedLine := strings.TrimSpace(line)
+		if strings.HasPrefix(trimmedLine, "RED") {
+			if !strings.Contains(trimmedLine, "Firebase") {
+				t.Fatalf("wrong template render, want: RED,Firebase, got: %s", trimmedLine)
+			}
+		} else if strings.HasPrefix(trimmedLine, "BLUE") {
+			if !strings.Contains(trimmedLine, "Gophers") {
+				t.Fatalf("wrong template render, want: BLUE,Gophers, got: %s", trimmedLine)
+			}
+		} else if strings.HasPrefix(trimmedLine, "GREEN") {
+			if !strings.Contains(trimmedLine, "Google") {
+				t.Fatalf("wrong template render, want: GREEN,Google, got: %s", trimmedLine)
+			}
+		}
+	}
+}
+
 func TestLoadPrompt_FileNotFound(t *testing.T) {
 	// Initialize a mock registry
 	reg := registry.New()
@@ -962,7 +1027,7 @@ func TestLoadPrompt_InvalidPromptFile(t *testing.T) {
 	// Create an invalid .prompt file
 	invalidPromptFile := filepath.Join(tempDir, "invalid.prompt")
 	invalidPromptContent := `invalid json content`
-	err := os.WriteFile(invalidPromptFile, []byte(invalidPromptContent), 0644)
+	err := os.WriteFile(invalidPromptFile, []byte(invalidPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create invalid prompt file: %v", err)
 	}
@@ -993,7 +1058,7 @@ description: A test prompt
 
 Hello, {{name}}!
 `
-	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0644)
+	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create mock prompt file: %v", err)
 	}
@@ -1018,7 +1083,7 @@ func TestLoadPromptFolder(t *testing.T) {
 	// Create mock prompt and partial files
 	mockPromptFile := filepath.Join(tempDir, "example.prompt")
 	mockSubDir := filepath.Join(tempDir, "subdir")
-	err := os.Mkdir(mockSubDir, 0755)
+	err := os.Mkdir(mockSubDir, 0o755)
 	if err != nil {
 		t.Fatalf("Failed to create subdirectory: %v", err)
 	}
@@ -1041,14 +1106,14 @@ output:
 Hello, {{name}}!
 `
 
-	err = os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0644)
+	err = os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create mock prompt file: %v", err)
 	}
 
 	// Create a mock prompt file in the subdirectory
 	mockSubPromptFile := filepath.Join(mockSubDir, "sub_example.prompt")
-	err = os.WriteFile(mockSubPromptFile, []byte(mockPromptContent), 0644)
+	err = os.WriteFile(mockSubPromptFile, []byte(mockPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create mock prompt file in subdirectory: %v", err)
 	}
@@ -1131,7 +1196,7 @@ You are a pirate!
 {{ role "user" }}
 Hello!
 `
-	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0644)
+	err := os.WriteFile(mockPromptFile, []byte(mockPromptContent), 0o644)
 	if err != nil {
 		t.Fatalf("Failed to create mock prompt file: %v", err)
 	}