Fix vendor/modules.txt using string matching

Author: owen-mc

vendor.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"golang.org/x/mod/modfile"
@@ -85,24 +86,30 @@ func stubModulesTxt() {
 	}
 
 	modFile := loadModFile(filepath.Join(modRoot, "go.mod"))
-
 	vdir := filepath.Join(modRoot, "vendor")
 
 	if gv := modFile.Go; gv != nil && semver.Compare("v"+gv.Version, "v1.14") >= 0 {
-		// If the Go version is at least 1.14, generate a dummy modules.txt using only the information
-		// in the go.mod file
+		// Find imports from all Go files in the project
+		usedPackages := findPackagesInSourceCode(modRoot)
 
 		generated := make(map[module.Version]bool)
 		var buf bytes.Buffer
 		for _, r := range modFile.Require {
-			// TODO: support replace lines
 			generated[r.Mod] = true
 			line := moduleLine(r.Mod, module.Version{})
 			buf.WriteString(line)
-
 			buf.WriteString("## explicit\n")
 
-			buf.WriteString(r.Mod.Path + "\n")
+			// List submodules that are actually used in the source code
+			submodulesForModule := findSubmodulesForModule(r.Mod.Path, usedPackages)
+			if len(submodulesForModule) > 0 {
+				for _, submod := range submodulesForModule {
+					buf.WriteString(submod + "\n")
+				}
+			} else {
+				// If no specific submodules are used, just list the module path itself
+				buf.WriteString(r.Mod.Path + "\n")
+			}
 		}
 
 		// Record unused and wildcard replacements at the end of the modules.txt file:
@@ -133,3 +140,110 @@ func stubModulesTxt() {
 		}
 	}
 }
+
+// findPackagesInSourceCode scans all Go files in the directory tree and extracts import paths
+func findPackagesInSourceCode(root string) map[string]bool {
+	packages := make(map[string]bool)
+
+	err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Skip vendor directory and hidden directories
+		if info.IsDir() && (info.Name() == "vendor" || strings.HasPrefix(info.Name(), ".")) {
+			return filepath.SkipDir
+		}
+
+		// Only process Go files
+		if !info.IsDir() && strings.HasSuffix(path, ".go") {
+			content, err := os.ReadFile(path)
+			if err != nil {
+				return err
+			}
+
+			// Simple parsing to find import statements
+			// This is a basic implementation - a more robust solution would use go/parser
+			lines := strings.Split(string(content), "\n")
+			inImport := false
+			for _, line := range lines {
+				line = strings.TrimSpace(line)
+
+				if strings.HasPrefix(line, "import (") {
+					inImport = true
+					continue
+				}
+
+				if inImport && strings.HasPrefix(line, ")") {
+					inImport = false
+					continue
+				}
+
+				if strings.HasPrefix(line, "import ") || inImport {
+					// Extract package path from import line
+					pkgPath := extractPackagePath(line)
+					if pkgPath != "" {
+						packages[pkgPath] = true
+					}
+				}
+			}
+		}
+		return nil
+	})
+
+	if err != nil {
+		log.Printf("Warning: error walking source directory: %v", err)
+	}
+
+	return packages
+}
+
+// extractPackagePath parses an import line to extract the package path
+func extractPackagePath(line string) string {
+	line = strings.TrimSpace(line)
+
+	// Skip if not an import line
+	if !(strings.HasPrefix(line, "import ") || strings.Contains(line, "\"") || strings.Contains(line, "`")) {
+		return ""
+	}
+
+	// Handle quoted imports
+	if strings.Contains(line, "\"") {
+		start := strings.Index(line, "\"")
+		end := strings.LastIndex(line, "\"")
+		if start >= 0 && end > start {
+			return line[start+1 : end]
+		}
+	}
+
+	// Handle backtick imports
+	if strings.Contains(line, "`") {
+		start := strings.Index(line, "`")
+		end := strings.LastIndex(line, "`")
+		if start >= 0 && end > start {
+			return line[start+1 : end]
+		}
+	}
+
+	return ""
+}
+
+// findSubmodulesForModule returns the submodules of a given module that are actually used in the source code
+func findSubmodulesForModule(modulePath string, usedPackages map[string]bool) []string {
+	var submodules []string
+
+	for pkg := range usedPackages {
+		// Check if this package belongs to the module
+		if strings.HasPrefix(pkg, modulePath) {
+			// Extract the part after modulePath
+			suffix := pkg[len(modulePath):]
+			matched, _ := regexp.MatchString(`^/v[1-9][0-9]*(/|$)`, suffix)
+
+			if !matched {
+				submodules = append(submodules, pkg)
+			}
+		}
+	}
+
+	return submodules
+}