fix: unify the precompile output to make it easier to parse and read. (…

…gnolang#1670)

<!-- please provide a detailed description of the changes made in this
pull request. -->
Fix gnolang#1636 

Under the hood, use `scanner.ErrorList` from the stdlib all the way to
store all errors with the filename and the position in the file. Note
that kind of error is already returned by `parser.ParserFile`.

For the `go build` output, instead of printing it like it is, parse it
and shift it to represent the related gno file.

Run the tests:
```
$ go test ./gnovm/cmd/gno -v -run Test_ScriptsPrecompile
```

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

- [x] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] 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>

gnovm/cmd/gno/precompile.go

@@ -2,8 +2,10 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
+	"go/scanner"
 	"log"
 	"os"
 	"path/filepath"
@@ -132,41 +134,43 @@ func execPrecompile(cfg *precompileCfg, args []string, io commands.IO) error {
 	}
 
 	opts := newPrecompileOptions(cfg)
-	errCount := 0
+	var errlist scanner.ErrorList
 	for _, filepath := range paths {
-		err = precompileFile(filepath, opts)
-		if err != nil {
-			err = fmt.Errorf("%s: precompile: %w", filepath, err)
-			io.ErrPrintfln("%s", err.Error())
-			errCount++
+		if err := precompileFile(filepath, opts); err != nil {
+			var fileErrlist scanner.ErrorList
+			if !errors.As(err, &fileErrlist) {
+				// Not an scanner.ErrorList: return immediately.
+				return fmt.Errorf("%s: precompile: %w", filepath, err)
+			}
+			errlist = append(errlist, fileErrlist...)
 		}
 	}
 
-	if errCount > 0 {
-		return fmt.Errorf("%d precompile errors", errCount)
-	}
-
-	if cfg.gobuild {
+	if errlist.Len() == 0 && cfg.gobuild {
 		paths, err := gnoPackagesFromArgs(args)
 		if err != nil {
 			return fmt.Errorf("list packages: %w", err)
 		}
 
-		errCount = 0
 		for _, pkgPath := range paths {
-			_ = pkgPath
-			err = goBuildFileOrPkg(pkgPath, cfg)
+			err := goBuildFileOrPkg(pkgPath, cfg)
 			if err != nil {
-				err = fmt.Errorf("%s: build pkg: %w", pkgPath, err)
-				io.ErrPrintfln("%s\n", err.Error())
-				errCount++
+				var fileErrlist scanner.ErrorList
+				if !errors.As(err, &fileErrlist) {
+					// Not an scanner.ErrorList: return immediately.
+					return fmt.Errorf("%s: build: %w", pkgPath, err)
+				}
+				errlist = append(errlist, fileErrlist...)
 			}
 		}
-		if errCount > 0 {
-			return fmt.Errorf("%d build errors", errCount)
-		}
 	}
 
+	if errlist.Len() > 0 {
+		for _, err := range errlist {
+			io.ErrPrintfln(err.Error())
+		}
+		return fmt.Errorf("%d precompile error(s)", errlist.Len())
+	}
 	return nil
 }
 
@@ -213,7 +217,7 @@ func precompileFile(srcPath string, opts *precompileOptions) error {
 	// preprocess.
 	precompileRes, err := gno.Precompile(string(source), tags, srcPath)
 	if err != nil {
-		return fmt.Errorf("%w", err)
+		return fmt.Errorf("precompile: %w", err)
 	}
 
 	// resolve target path

gnovm/cmd/gno/testdata/gno_precompile/03_gno_files_parse_error.txtar

@@ -3,8 +3,10 @@
 ! gno precompile .
 
 ! stdout .+
-stderr 'precompile: parse: main.gno:3:1: expected declaration, found invalid'
-stderr 'precompile: parse: sub/sub.gno:3:1: expected declaration, found invalid'
+stderr '^main.gno:3:1: expected declaration, found invalid$'
+stderr '^main.gno:7:2: expected declaration, found wrong$'
+stderr '^sub/sub.gno:3:1: expected declaration, found invalid$'
+stderr '^3 precompile error\(s\)$'
 
 # no *.gen.go files are created
 ! exec test -f main.gno.gen.go
@@ -15,8 +17,10 @@ package main
 
 invalid
 
-func main() {}
-
+func main() {
+	var x = 1
+	wrong
+}
 -- sub/sub.gno --
 package sub
 

gnovm/cmd/gno/testdata/gno_precompile/07_build_flag_with_build_error.txtar

@@ -3,7 +3,9 @@
 ! gno precompile -gobuild .
 
 ! stdout .+
-stderr './main.gno.gen.go:8:6: x declared and not used'
+stderr '^./main.gno:4:6: x declared and not used$'
+stderr '^./main.gno:5:6: y declared and not used$'
+stderr '^2 precompile error\(s\)$'
 
 cmp main.gno.gen.go main.gno.gen.go.golden
 cmp sub/sub.gno.gen.go sub/sub.gno.gen.go.golden
@@ -13,6 +15,7 @@ package main
 
 func main() {
 	var x = 1
+	var y = 2
 }
 -- sub/sub.gno --
 package sub
@@ -25,6 +28,7 @@ package main
 
 func main() {
 	var x = 1
+	var y = 2
 }
 -- sub/sub.gno.gen.go.golden --
 // Code generated by github.com/gnolang/gno. DO NOT EDIT.

gnovm/cmd/gno/testdata/gno_precompile/08_build_flag_with_parse_error.txtar

@@ -3,7 +3,7 @@
 ! gno precompile -gobuild .
 
 ! stdout .+
-stderr 'main.gno: precompile: parse: main.gno:3:1: expected declaration, found invalid'
+stderr '^main.gno:3:1: expected declaration, found invalid$'
 
 # no *.gen.go files are created
 ! exec test -f main.gno.gen.go
@@ -12,3 +12,7 @@ stderr 'main.gno: precompile: parse: main.gno:3:1: expected declaration, found i
 package main
 
 invalid
+
+func main() {
+	var x = 1
+}

gnovm/cmd/gno/testdata/gno_precompile/09_gno_files_whitelist_error.txtar

@@ -3,8 +3,9 @@
 ! gno precompile .
 
 ! stdout .+
-stderr 'main.gno: precompile: import "xxx" is not in the whitelist'
-stderr 'sub/sub.gno: precompile: import "xxx" is not in the whitelist'
+stderr '^main.gno:5:2: import "xxx" is not in the whitelist$'
+stderr '^sub/sub.gno:3:8: import "xxx" is not in the whitelist$'
+stderr '^2 precompile error\(s\)$'
 
 # no *.gen.go files are created
 ! exec test -f main.gno.gen.go

gnovm/pkg/gnolang/precompile.go

@@ -6,11 +6,14 @@ import (
 	"go/ast"
 	"go/format"
 	"go/parser"
+	goscanner "go/scanner"
 	"go/token"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 
 	"go.uber.org/multierr"
@@ -148,8 +151,6 @@ func PrecompileAndCheckMempkg(mempkg *std.MemPackage) error {
 }
 
 func Precompile(source string, tags string, filename string) (*precompileResult, error) {
-	var out bytes.Buffer
-
 	fset := token.NewFileSet()
 	f, err := parser.ParseFile(fset, filename, source, parser.ParseComments)
 	if err != nil {
@@ -161,18 +162,19 @@ func Precompile(source string, tags string, filename string) (*precompileResult,
 
 	transformed, err := precompileAST(fset, f, shouldCheckWhitelist)
 	if err != nil {
-		return nil, fmt.Errorf("%w", err)
+		return nil, fmt.Errorf("precompileAST: %w", err)
 	}
 
 	header := "// Code generated by github.com/gnolang/gno. DO NOT EDIT.\n\n"
 	if tags != "" {
 		header += "//go:build " + tags + "\n\n"
 	}
-	_, err = out.WriteString(header)
+	var out bytes.Buffer
+	out.WriteString(header)
+	err = format.Node(&out, fset, transformed)
 	if err != nil {
-		return nil, fmt.Errorf("write to buffer: %w", err)
+		return nil, fmt.Errorf("format.Node: %w", err)
 	}
-	err = format.Node(&out, fset, transformed)
 
 	res := &precompileResult{
 		Imports:    f.Imports,
@@ -202,7 +204,7 @@ func PrecompileVerifyFile(path string, gofmtBinary string) error {
 //
 // This method is the most efficient to detect errors but requires that
 // all the import are valid and available.
-func PrecompileBuildPackage(fileOrPkg string, goBinary string) error {
+func PrecompileBuildPackage(fileOrPkg, goBinary string) error {
 	// TODO: use cmd/compile instead of exec?
 	// TODO: find the nearest go.mod file, chdir in the same folder, rim prefix?
 	// TODO: temporarily create an in-memory go.mod or disable go modules for gno?
@@ -213,7 +215,7 @@ func PrecompileBuildPackage(fileOrPkg string, goBinary string) error {
 
 	info, err := os.Stat(fileOrPkg)
 	if err != nil {
-		return fmt.Errorf("invalid file or package path: %w", err)
+		return fmt.Errorf("invalid file or package path %s: %w", fileOrPkg, err)
 	}
 	if !info.IsDir() {
 		file := fileOrPkg
@@ -223,7 +225,7 @@ func PrecompileBuildPackage(fileOrPkg string, goBinary string) error {
 		goGlob := filepath.Join(pkgDir, "*.go")
 		goMatches, err := filepath.Glob(goGlob)
 		if err != nil {
-			return fmt.Errorf("glob: %w", err)
+			return fmt.Errorf("glob %s: %w", goGlob, err)
 		}
 		for _, goMatch := range goMatches {
 			switch {
@@ -246,16 +248,53 @@ func PrecompileBuildPackage(fileOrPkg string, goBinary string) error {
 		cmd.Dir = rootDir
 	}
 	out, err := cmd.CombinedOutput()
-	if err != nil {
-		fmt.Fprintln(os.Stderr, string(out))
-		return fmt.Errorf("std go compiler: %w", err)
+	if _, ok := err.(*exec.ExitError); ok {
+		// exit error
+		return parseGoBuildErrors(string(out))
 	}
+	return err
+}
 
-	return nil
+var errorRe = regexp.MustCompile(`(?m)^(\S+):(\d+):(\d+): (.+)$`)
+
+// parseGoBuildErrors returns a scanner.ErrorList filled with all errors found
+// in out, which is supposed to be the output of the `go build` command.
+// Each errors are translated into their correlated gno files, by:
+// - changing the filename from *.gno.gen.go to *.gno
+// - shifting line number according to the added header in generated go files
+// (see [Precompile] for that header).
+func parseGoBuildErrors(out string) error {
+	var errList goscanner.ErrorList
+	matches := errorRe.FindAllStringSubmatch(out, -1)
+	for _, match := range matches {
+		filename := match[1]
+		line, err := strconv.Atoi(match[2])
+		if err != nil {
+			return fmt.Errorf("parse line go build error %s: %w", match, err)
+		}
+
+		column, err := strconv.Atoi(match[3])
+		if err != nil {
+			return fmt.Errorf("parse column go build error %s: %w", match, err)
+		}
+		msg := match[4]
+		errList.Add(token.Position{
+			// Remove .gen.go extension, we want to target the gno file
+			Filename: strings.TrimSuffix(filename, ".gen.go"),
+			// Shift the 4 lines header added in *.gen.go files.
+			// NOTE(tb): the 4 lines shift below assumes there's always a //go:build
+			// directive. But the tags are optional in the Precompile() function
+			// so that leaves some doubts... We might want something more reliable than
+			// constants to shift lines.
+			Line:   line - 4,
+			Column: column,
+		}, msg)
+	}
+	return errList.Err()
 }
 
 func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.Node, error) {
-	var errs error
+	var errs goscanner.ErrorList
 
 	imports := astutil.Imports(fset, f)
 
@@ -294,7 +333,7 @@ func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.N
 					continue
 				}
 
-				errs = multierr.Append(errs, fmt.Errorf("import %q is not in the whitelist", importPath))
+				errs.Add(fset.Position(importSpec.Pos()), fmt.Sprintf("import %q is not in the whitelist", importPath))
 			}
 		}
 	}
@@ -307,7 +346,7 @@ func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.N
 			// std package
 			if importPath == GnoStdPkgBefore {
 				if !astutil.RewriteImport(fset, f, GnoStdPkgBefore, GnoStdPkgAfter) {
-					errs = multierr.Append(errs, fmt.Errorf("failed to replace the %q package with %q", GnoStdPkgBefore, GnoStdPkgAfter))
+					errs.Add(fset.Position(importSpec.Pos()), fmt.Sprintf("failed to replace the %q package with %q", GnoStdPkgBefore, GnoStdPkgAfter))
 				}
 			}
 
@@ -316,7 +355,7 @@ func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.N
 				target := GnoPackagePrefixAfter + strings.TrimPrefix(importPath, GnoPackagePrefixBefore)
 
 				if !astutil.RewriteImport(fset, f, importPath, target) {
-					errs = multierr.Append(errs, fmt.Errorf("failed to replace the %q package with %q", importPath, target))
+					errs.Add(fset.Position(importSpec.Pos()), fmt.Sprintf("failed to replace the %q package with %q", importPath, target))
 				}
 			}
 
@@ -325,7 +364,7 @@ func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.N
 				target := GnoRealmPkgsPrefixAfter + strings.TrimPrefix(importPath, GnoRealmPkgsPrefixBefore)
 
 				if !astutil.RewriteImport(fset, f, importPath, target) {
-					errs = multierr.Append(errs, fmt.Errorf("failed to replace the %q package with %q", importPath, target))
+					errs.Add(fset.Position(importSpec.Pos()), fmt.Sprintf("failed to replace the %q package with %q", importPath, target))
 				}
 			}
 		}
@@ -344,6 +383,5 @@ func precompileAST(fset *token.FileSet, f *ast.File, checkWhitelist bool) (ast.N
 			return true
 		},
 	)
-
-	return node, errs
+	return node, errs.Err()
 }