loader: handle `go list` errors inside TinyGo

Instead of exiting with an error, handle these errors internally.
This will enable a few improvements in the future.

errors_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -16,6 +17,10 @@ import (
 func TestErrors(t *testing.T) {
 	for _, name := range []string{
 		"cgo",
+		"loader-importcycle",
+		"loader-invaliddep",
+		"loader-invalidpackage",
+		"loader-nopackage",
 		"syntax",
 		"types",
 	} {
@@ -57,11 +62,22 @@ func testErrorMessages(t *testing.T, filename string) {
 	actual := strings.TrimRight(buf.String(), "\n")
 
 	// Check whether the error is as expected.
-	if actual != expected {
+	if canonicalizeErrors(actual) != canonicalizeErrors(expected) {
 		t.Errorf("expected error:\n%s\ngot:\n%s", indentText(expected, "> "), indentText(actual, "> "))
 	}
 }
 
+func canonicalizeErrors(text string) string {
+	// Fix for Windows: replace all backslashes with forward slashes so that
+	// paths will be the same as on POSIX systems.
+	// (It may also change some other backslashes, but since this is only for
+	// comparing text it should be fine).
+	if runtime.GOOS == "windows" {
+		text = strings.ReplaceAll(text, "\\", "/")
+	}
+	return text
+}
+
 // Indent the given text with a given indentation string.
 func indentText(text, indent string) string {
 	return indent + strings.ReplaceAll(text, "\n", "\n"+indent)

loader/loader.go

@@ -128,7 +128,7 @@ func Load(config *compileopts.Config, inputPkg string, typeChecker types.Config)
 	}
 
 	// List the dependencies of this package, in raw JSON format.
-	extraArgs := []string{"-json", "-deps"}
+	extraArgs := []string{"-json", "-deps", "-e"}
 	if config.TestConfig.CompileTestBinary {
 		extraArgs = append(extraArgs, "-test")
 	}
@@ -149,6 +149,7 @@ func Load(config *compileopts.Config, inputPkg string, typeChecker types.Config)
 
 	// Parse the returned json from `go list`.
 	decoder := json.NewDecoder(buf)
+	var pkgErrors []error
 	for {
 		pkg := &Package{
 			program:      p,
@@ -188,6 +189,12 @@ func Load(config *compileopts.Config, inputPkg string, typeChecker types.Config)
 					pos.Filename = strings.Join(fields[:len(fields)-1], ":")
 					pos.Line, _ = strconv.Atoi(fields[len(fields)-1])
 				}
+				if abs, err := filepath.Abs(pos.Filename); err == nil {
+					// Make the path absolute, so that error messages will be
+					// prettier (it will be turned back into a relative path
+					// when printing the error).
+					pos.Filename = abs
+				}
 				pos.Filename = p.getOriginalPath(pos.Filename)
 			}
 			err := scanner.Error{
@@ -195,10 +202,11 @@ func Load(config *compileopts.Config, inputPkg string, typeChecker types.Config)
 				Msg: pkg.Error.Err,
 			}
 			if len(pkg.Error.ImportStack) != 0 {
-				return nil, Error{
+				pkgErrors = append(pkgErrors, Error{
 					ImportStack: pkg.Error.ImportStack,
 					Err:         err,
-				}
+				})
+				continue
 			}
 			return nil, err
 		}
@@ -241,6 +249,13 @@ func Load(config *compileopts.Config, inputPkg string, typeChecker types.Config)
 		p.Packages[pkg.ImportPath] = pkg
 	}
 
+	if len(pkgErrors) != 0 {
+		// TODO: use errors.Join in Go 1.20.
+		return nil, Errors{
+			Errs: pkgErrors,
+		}
+	}
+
 	if config.TestConfig.CompileTestBinary && !strings.HasSuffix(p.sorted[len(p.sorted)-1].ImportPath, ".test") {
 		// Trying to compile a test binary but there are no test files in this
 		// package.

main.go

@@ -1340,15 +1340,31 @@ func printCompilerError(err error, logln func(...interface{}), wd string) {
 			}
 		}
 	case loader.Errors:
-		logln("#", err.Pkg.ImportPath)
+		// Parser errors, typechecking errors, or `go list` errors.
+		// err.Pkg is nil for `go list` errors.
+		if err.Pkg != nil {
+			logln("#", err.Pkg.ImportPath)
+		}
 		for _, err := range err.Errs {
 			printCompilerError(err, logln, wd)
 		}
 	case loader.Error:
-		logln(err.Err.Error())
-		logln("package", err.ImportStack[0])
-		for _, pkgPath := range err.ImportStack[1:] {
-			logln("\timports", pkgPath)
+		if err.Err.Pos.Filename != "" {
+			// Probably a syntax error in a dependency.
+			printCompilerError(err.Err, logln, wd)
+		} else {
+			// Probably an "import cycle not allowed" error.
+			logln("package", err.ImportStack[0])
+			for i := 1; i < len(err.ImportStack); i++ {
+				pkgPath := err.ImportStack[i]
+				if i == len(err.ImportStack)-1 {
+					// last package
+					logln("\timports", pkgPath+": "+err.Err.Error())
+				} else {
+					// not the last pacakge
+					logln("\timports", pkgPath)
+				}
+			}
 		}
 	case *builder.MultiError:
 		for _, err := range err.Errs {

testdata/errors/importcycle/cycle.go

@@ -0,0 +1,3 @@
+package importcycle
+
+import _ "github.com/tinygo-org/tinygo/testdata/errors/importcycle"

testdata/errors/invaliddep/invaliddep.go

@@ -0,0 +1 @@
+ppackage // syntax error

testdata/errors/loader-importcycle.go

@@ -0,0 +1,10 @@
+package main
+
+import _ "github.com/tinygo-org/tinygo/testdata/errors/importcycle"
+
+func main() {
+}
+
+// ERROR: package command-line-arguments
+// ERROR: 	imports github.com/tinygo-org/tinygo/testdata/errors/importcycle
+// ERROR: 	imports github.com/tinygo-org/tinygo/testdata/errors/importcycle: import cycle not allowed

testdata/errors/loader-invaliddep.go

@@ -0,0 +1,8 @@
+package main
+
+import _ "github.com/tinygo-org/tinygo/testdata/errors/invaliddep"
+
+func main() {
+}
+
+// ERROR: invaliddep/invaliddep.go:1:1: expected 'package', found ppackage

testdata/errors/loader-invalidpackage.go

@@ -0,0 +1,3 @@
+ppackage // syntax error
+
+// ERROR: loader-invalidpackage.go:1:1: expected 'package', found ppackage

testdata/errors/loader-nopackage.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	_ "github.com/tinygo-org/tinygo/testdata/errors/non-existing-package"
+	_ "github.com/tinygo-org/tinygo/testdata/errors/non-existing-package-2"
+)
+
+func main() {
+}
+
+// ERROR: loader-nopackage.go:4:2: no required module provides package github.com/tinygo-org/tinygo/testdata/errors/non-existing-package; to add it:
+// ERROR: 	go get github.com/tinygo-org/tinygo/testdata/errors/non-existing-package
+// ERROR: loader-nopackage.go:5:2: no required module provides package github.com/tinygo-org/tinygo/testdata/errors/non-existing-package-2; to add it:
+// ERROR: 	go get github.com/tinygo-org/tinygo/testdata/errors/non-existing-package-2