feat: use modfile package to write modfile (gnolang#1077)

The previous implementation manually iterates over the `Require` and
`Replace` and writes them in the string var to construct the modfile,
which is very inefficient and doesn't handles comments and other cases.

Changed it use `modfile` package to write modfile(gno.mod/go.mod). It
uses `*modfile.FileSyntax`. Copied few methods from `modfile` package to
manipulate `*modfile.FileSyntax`.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

---------

Co-authored-by: Manfred Touron <94029+moul@users.noreply.github.com>

gnovm/cmd/gno/mod.go

@@ -126,7 +126,7 @@ func execModDownload(cfg *modDownloadCfg, args []string, io *commands.IO) error
 	}
 
 	// write go.mod file
-	err = gomod.WriteToPath(filepath.Join(path, "go.mod"))
+	err = gomod.Write(filepath.Join(path, "go.mod"))
 	if err != nil {
 		return fmt.Errorf("write go.mod file: %w", err)
 	}

gnovm/pkg/gnomod/file.go

@@ -1,3 +1,12 @@
+// Some part of file is copied and modified from
+// golang.org/x/mod/modfile/read.go
+//
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in here[1].
+//
+// [1]: https://cs.opensource.google/go/x/mod/+/master:LICENSE
+
 package gnomod
 
 import (
@@ -24,6 +33,100 @@ type File struct {
 	Syntax *modfile.FileSyntax
 }
 
+// AddRequire sets the first require line for path to version vers,
+// preserving any existing comments for that line and removing all
+// other lines for path.
+//
+// If no line currently exists for path, AddRequire adds a new line
+// at the end of the last require block.
+func (f *File) AddRequire(path, vers string) error {
+	need := true
+	for _, r := range f.Require {
+		if r.Mod.Path == path {
+			if need {
+				r.Mod.Version = vers
+				updateLine(r.Syntax, "require", modfile.AutoQuote(path), vers)
+				need = false
+			} else {
+				markLineAsRemoved(r.Syntax)
+				*r = modfile.Require{}
+			}
+		}
+	}
+
+	if need {
+		f.AddNewRequire(path, vers, false)
+	}
+	return nil
+}
+
+// AddNewRequire adds a new require line for path at version vers at the end of
+// the last require block, regardless of any existing require lines for path.
+func (f *File) AddNewRequire(path, vers string, indirect bool) {
+	line := addLine(f.Syntax, nil, "require", modfile.AutoQuote(path), vers)
+	r := &modfile.Require{
+		Mod:    module.Version{Path: path, Version: vers},
+		Syntax: line,
+	}
+	setIndirect(r, indirect)
+	f.Require = append(f.Require, r)
+}
+
+func (f *File) AddModuleStmt(path string) error {
+	if f.Syntax == nil {
+		f.Syntax = new(modfile.FileSyntax)
+	}
+	if f.Module == nil {
+		f.Module = &modfile.Module{
+			Mod:    module.Version{Path: path},
+			Syntax: addLine(f.Syntax, nil, "module", modfile.AutoQuote(path)),
+		}
+	} else {
+		f.Module.Mod.Path = path
+		updateLine(f.Module.Syntax, "module", modfile.AutoQuote(path))
+	}
+	return nil
+}
+
+func (f *File) AddComment(text string) {
+	if f.Syntax == nil {
+		f.Syntax = new(modfile.FileSyntax)
+	}
+	f.Syntax.Stmt = append(f.Syntax.Stmt, &modfile.CommentBlock{
+		Comments: modfile.Comments{
+			Before: []modfile.Comment{
+				{
+					Token: text,
+				},
+			},
+		},
+	})
+}
+
+func (f *File) AddReplace(oldPath, oldVers, newPath, newVers string) error {
+	return addReplace(f.Syntax, &f.Replace, oldPath, oldVers, newPath, newVers)
+}
+
+func (f *File) DropRequire(path string) error {
+	for _, r := range f.Require {
+		if r.Mod.Path == path {
+			markLineAsRemoved(r.Syntax)
+			*r = modfile.Require{}
+		}
+	}
+	return nil
+}
+
+func (f *File) DropReplace(oldPath, oldVers string) error {
+	for _, r := range f.Replace {
+		if r.Old.Path == oldPath && r.Old.Version == oldVers {
+			markLineAsRemoved(r.Syntax)
+			*r = modfile.Replace{}
+		}
+	}
+	return nil
+}
+
 // Validate validates gno.mod
 func (f *File) Validate() error {
 	if f.Module == nil {
@@ -73,13 +176,8 @@ func (f *File) FetchDeps(path string, remote string, verbose bool) error {
 			return fmt.Errorf("writepackage: %w", err)
 		}
 
-		modFile := &File{
-			Module: &modfile.Module{
-				Mod: module.Version{
-					Path: mod.Path,
-				},
-			},
-		}
+		modFile := new(File)
+		modFile.AddModuleStmt(mod.Path)
 		for _, req := range requirements {
 			path := req[1 : len(req)-1] // trim leading and trailing `"`
 			if strings.HasSuffix(path, modFile.Module.Mod.Path) {
@@ -92,13 +190,7 @@ func (f *File) FetchDeps(path string, remote string, verbose bool) error {
 
 			if strings.HasPrefix(path, gnolang.ImportPrefix) {
 				path = strings.TrimPrefix(path, gnolang.ImportPrefix+"/examples/")
-				modFile.Require = append(modFile.Require, &modfile.Require{
-					Mod: module.Version{
-						Path:    path,
-						Version: "v0.0.0", // TODO: Use latest?
-					},
-					Indirect: true,
-				})
+				modFile.AddNewRequire(path, "v0.0.0-latest", true)
 			}
 		}
 
@@ -112,7 +204,7 @@ func (f *File) FetchDeps(path string, remote string, verbose bool) error {
 		}
 		pkgPath := PackageDir(path, mod)
 		goModFilePath := filepath.Join(pkgPath, "go.mod")
-		err = goMod.WriteToPath(goModFilePath)
+		err = goMod.Write(goModFilePath)
 		if err != nil {
 			return err
 		}
@@ -121,42 +213,14 @@ func (f *File) FetchDeps(path string, remote string, verbose bool) error {
 	return nil
 }
 
-// WriteToPath writes file to the given absolute file path
-// TODO: Find better way to do this. Try to use `modfile`
-// package to manage this.
-func (f *File) WriteToPath(absFilePath string) error {
-	if f.Module == nil {
-		return errors.New("writing go.mod: module not found")
-	}
-
-	data := "module " + f.Module.Mod.Path + "\n"
-
-	if f.Go != nil {
-		data += "\ngo " + f.Go.Version + "\n"
-	}
-
-	if f.Require != nil {
-		data += "\nrequire (" + "\n"
-		for _, req := range f.Require {
-			data += "\t" + req.Mod.Path + " " + req.Mod.Version + "\n"
-		}
-		data += ")\n"
-	}
-
-	if f.Replace != nil {
-		data += "\nreplace (" + "\n"
-		for _, rep := range f.Replace {
-			data += "\t" + rep.Old.Path + " " + rep.Old.Version +
-				" => " + rep.New.Path + "\n"
-		}
-		data += ")\n"
-	}
-
-	err := os.WriteFile(absFilePath, []byte(data), 0o644)
+// writes file to the given absolute file path
+func (f *File) Write(fname string) error {
+	f.Syntax.Cleanup()
+	data := modfile.Format(f.Syntax)
+	err := os.WriteFile(fname, data, 0o644)
 	if err != nil {
-		return fmt.Errorf("writefile %q: %w", absFilePath, err)
+		return fmt.Errorf("writefile %q: %w", fname, err)
 	}
-
 	return nil
 }
 

gnovm/pkg/gnomod/gnomod.go

@@ -100,7 +100,7 @@ func GnoToGoMod(f File) (*File, error) {
 
 	if strings.HasPrefix(f.Module.Mod.Path, gnolang.GnoRealmPkgsPrefixBefore) ||
 		strings.HasPrefix(f.Module.Mod.Path, gnolang.GnoPackagePrefixBefore) {
-		f.Module.Mod.Path = gnolang.ImportPrefix + "/examples/" + f.Module.Mod.Path
+		f.AddModuleStmt(gnolang.ImportPrefix + "/examples/" + f.Module.Mod.Path)
 	}
 
 	for i := range f.Require {
@@ -113,20 +113,17 @@ func GnoToGoMod(f File) (*File, error) {
 		path := f.Require[i].Mod.Path
 		if strings.HasPrefix(f.Require[i].Mod.Path, gnolang.GnoRealmPkgsPrefixBefore) ||
 			strings.HasPrefix(f.Require[i].Mod.Path, gnolang.GnoPackagePrefixBefore) {
-			f.Require[i].Mod.Path = gnolang.ImportPrefix + "/examples/" + f.Require[i].Mod.Path
+			// Add dependency with a modified import path
+			f.AddRequire(gnolang.ImportPrefix+"/examples/"+f.Require[i].Mod.Path, f.Require[i].Mod.Version)
 		}
-
-		f.Replace = append(f.Replace, &modfile.Replace{
-			Old: module.Version{
-				Path:    f.Require[i].Mod.Path,
-				Version: f.Require[i].Mod.Version,
-			},
-			New: module.Version{
-				Path: filepath.Join(gnoModPath, path),
-			},
-		})
+		f.AddReplace(f.Require[i].Mod.Path, f.Require[i].Mod.Version, filepath.Join(gnoModPath, path), "")
+		// Remove the old require since the new dependency was added above
+		f.DropRequire(f.Require[i].Mod.Path)
 	}
 
+	// Remove replacements that are not replaced by directories.
+	//
+	// Explanation:
 	// By this stage every replacement should be replace by dir.
 	// If not replaced by dir, remove it.
 	//
@@ -153,14 +150,11 @@ func GnoToGoMod(f File) (*File, error) {
 	// ```
 	//
 	// Remove `gno.land/p/demo/avl v1.2.3  => gno.land/p/demo/avl v3.2.1`.
-	repl := make([]*modfile.Replace, 0, len(f.Replace))
 	for _, r := range f.Replace {
 		if !modfile.IsDirectoryPath(r.New.Path) {
-			continue
+			f.DropReplace(r.Old.Path, r.Old.Version)
 		}
-		repl = append(repl, r)
 	}
-	f.Replace = repl
 
 	return &f, nil
 }
@@ -215,14 +209,9 @@ func CreateGnoModFile(rootDir, modPath string) error {
 		return err
 	}
 
-	modFile := &File{
-		Module: &modfile.Module{
-			Mod: module.Version{
-				Path: modPath,
-			},
-		},
-	}
-	modFile.WriteToPath(filepath.Join(rootDir, "gno.mod"))
+	modfile := new(File)
+	modfile.AddModuleStmt(modPath)
+	modfile.Write(filepath.Join(rootDir, "gno.mod"))
 
 	return nil
 }