fix: preserve build tags in generated files

CHANGELOG.md

@@ -5,7 +5,15 @@ All notable changes to this project will be documented in this file.
 This project follows the [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) format
 and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [0.1.0] — Unreleased
+## [0.1.1] — Unreleased
+
+### Fixed
+- **dependgen**: Build tags (`//go:build` and `// +build` directives) are now correctly preserved from source test files to generated `*_depend_test.go` files ([#1](https://github.com/srgg/testify/issues/1))
+  - Scans all comment groups before package declaration to find build constraints
+  - Handles files with copyright notices or other comments before build tags
+  - Ensures generated files maintain the same build constraints as source files
+
+## [0.1.0] — 2024-11-03
 
 Initial public release of `testify/depend`, bringing first-class dependency management
 to Go test suites built with `stretchr/testify`.

depend/cmd/dependgen/integration_test.go

@@ -530,6 +530,101 @@ func TestSuite(t *testing.T) {
 	}
 }
 
+func (s *IntegrationSuite) TestBuildTagsPreservedInGeneratedFile() {
+	// GOAL: Verify build tags are preserved from source file to generated file
+	// Fixes GitHub issue #1: https://github.com/srgg/testify/issues/1
+	//
+	// TEST SCENARIO: Create test file with //go:build and // +build tags → run dependgen →
+	// generated file preserves both build tags before the "Code generated" comment
+
+	testCases := []struct {
+		name        string
+		fileContent string
+	}{
+		{
+			name: "Build tags as first comment group",
+			fileContent: `//go:build test
+// +build test
+
+package test
+
+import (
+	"testing"
+	"github.com/srgg/testify/depend"
+	"github.com/stretchr/testify/suite"
+)
+
+type MySuite struct {
+	suite.Suite
+}
+
+func (s *MySuite) TestA() {}
+func (s *MySuite) TestB() {}
+
+func TestMySuite(t *testing.T) {
+	depend.RunSuite(t, new(MySuite))
+}`,
+		},
+		{
+			name: "Build tags after copyright comment",
+			fileContent: `// Copyright 2024 Example Corp
+// All rights reserved
+
+//go:build test
+// +build test
+
+package test
+
+import (
+	"testing"
+	"github.com/srgg/testify/depend"
+	"github.com/stretchr/testify/suite"
+)
+
+type MySuite struct {
+	suite.Suite
+}
+
+func (s *MySuite) TestA() {}
+func (s *MySuite) TestB() {}
+
+func TestMySuite(t *testing.T) {
+	depend.RunSuite(t, new(MySuite))
+}`,
+		},
+	}
+
+	for _, tc := range testCases {
+		s.Run(tc.name, func() {
+			testDir := s.TempDir().Build()
+
+			testFile := filepath.Join(testDir, "suite_test.go")
+			err := os.WriteFile(testFile, []byte(tc.fileContent), 0644)
+			s.Require().NoError(err, "MUST write test file")
+
+			// Run dependgen in auto-detect mode
+			output, err := s.runDependgen(testDir, []string{"-v"}, map[string]string{"GOFILE": "suite_test.go"})
+			s.Assert().NoError(err, "MUST generate successfully: %s", output)
+
+			// Verify generated file contains both build tags
+			generatedCode := s.assertGeneratedFile(testDir, "suite_depend_test.go",
+				"//go:build test",
+				"// +build test",
+				"Code generated by dependgen",
+				"MySuiteTestRegistry")
+
+			// Verify build tags appear BEFORE the generated code comment (critical for Go toolchain)
+			s.Assert().Regexp(`(?s)//go:build test\s+// \+build test\s+// Code generated by dependgen`, generatedCode,
+				"MUST have build tags before generated code comment")
+
+			// Copyright should NOT be copied to generated file
+			if tc.name == "Build tags after copyright comment" {
+				s.Assert().NotContains(generatedCode, "Copyright", "MUST NOT copy copyright to generated file")
+			}
+		})
+	}
+}
+
 func TestDependgenSuite(t *testing.T) {
 	suite.Run(t, new(IntegrationSuite))
 }

depend/cmd/dependgen/scanner.go

@@ -22,18 +22,21 @@ type SuiteInfo struct {
 	Package    string           // Package name (e.g., "depend")
 	Tests      []TestMethodInfo // Test methods in this suite
 	SourceFile string           // Source file where suite was defined (e.g., "runtime_test.go")
+	BuildTags  []string         // Build tags from source file (e.g., ["//go:build test", "// +build test"])
 }
 
 // suiteCollector collects suite information during scanning.
 // It encapsulates the logic for tracking suites and their test methods.
 type suiteCollector struct {
-	suites map[string]SuiteInfo
+	suites           map[string]SuiteInfo
+	srcFileBuildTags map[string][]string // sourceFile -> buildTags
 }
 
 // newSuiteCollector creates a new suite collector.
 func newSuiteCollector() *suiteCollector {
 	return &suiteCollector{
-		suites: make(map[string]SuiteInfo),
+		suites:           make(map[string]SuiteInfo),
+		srcFileBuildTags: make(map[string][]string),
 	}
 }
 
@@ -46,6 +49,11 @@ func (c *suiteCollector) addSuiteName(name string) {
 	}
 }
 
+// setBuildTags stores build tags for a source file.
+func (c *suiteCollector) setBuildTags(sourceFile string, buildTags []string) {
+	c.srcFileBuildTags[sourceFile] = buildTags
+}
+
 // addTest adds a test method to a suite.
 // If the suite doesn't have metadata set, it sets them.
 func (c *suiteCollector) addTest(suiteName, packageName, sourceFile string, test TestMethodInfo) {
@@ -59,6 +67,10 @@ func (c *suiteCollector) addTest(suiteName, packageName, sourceFile string, test
 	if info.SourceFile == "" {
 		info.SourceFile = sourceFile
 	}
+	// Set build tags from the map if not already set
+	if info.BuildTags == nil {
+		info.BuildTags = c.srcFileBuildTags[sourceFile]
+	}
 	info.Tests = append(info.Tests, test)
 	c.suites[suiteName] = info
 }
@@ -141,8 +153,12 @@ func (s *SuiteScanner) processFile(f *ast.File, sourceFile string) (bool, error)
 		return false, nil
 	}
 
-	// Extract package name from the AST file
+	// Extract package name and build tags from the AST file
 	packageName := f.Name.Name
+	buildTags := extractBuildTags(f)
+
+	// Store build tags for this source file
+	s.collector.setBuildTags(sourceFile, buildTags)
 
 	// Single-pass AST traversal: process both type declarations and method declarations in one iteration
 	for _, decl := range f.Decls {
@@ -313,3 +329,34 @@ func parseDependsOnComment(commentText string) []string {
 	}
 	return deps
 }
+
+// extractBuildTags extracts build constraint comments from an AST file.
+// It looks for //go:build and // +build directives at the top of the file.
+// These comments appear before the package declaration and must be preserved
+// in generated files to maintain build constraints.
+//
+// Returns a slice of complete comment lines including the "//" prefix.
+// Example output: ["//go:build test", "// +build test"]
+func extractBuildTags(f *ast.File) []string {
+	var buildTags []string
+
+	// Build tags can appear in any comment group before the package declaration.
+	// Scan all comment groups that appear before the package keyword.
+	for _, commentGroup := range f.Comments {
+		// Stop if we've reached comments after the package declaration
+		if commentGroup.Pos() >= f.Package {
+			break
+		}
+
+		// Check each comment in the group for build tags
+		for _, comment := range commentGroup.List {
+			text := comment.Text
+			// Look for build constraint comments
+			if strings.HasPrefix(text, "//go:build") || strings.HasPrefix(text, "// +build") {
+				buildTags = append(buildTags, text)
+			}
+		}
+	}
+
+	return buildTags
+}