cmd/go: include imports in 'go list -e' output even after parse errors

If we aren't able to load imports from one file in a package due to a
parse error (scanner.ErrorList), 'go list -e' should still list
imports in other files.

Fixes #35973

Change-Id: I59f171877949bb7afaf252b6c8a970de22e60c7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/210097
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/load/pkg.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"go/build"
+	"go/scanner"
 	"go/token"
 	"io/ioutil"
 	"os"
@@ -1519,17 +1520,30 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		p.Internal.LocalPrefix = dirToImportPath(p.Dir)
 	}
 
+	// setError sets p.Error if it hasn't already been set. We may proceed
+	// after encountering some errors so that 'go list -e' has more complete
+	// output. If there's more than one error, we should report the first.
+	setError := func(err error) {
+		if p.Error == nil {
+			p.Error = &PackageError{
+				ImportStack: stk.Copy(),
+				Err:         err,
+			}
+		}
+	}
+
 	if err != nil {
 		if _, ok := err.(*build.NoGoError); ok {
 			err = &NoGoError{Package: p}
 		}
 		p.Incomplete = true
-		err = base.ExpandScanner(err)
-		p.Error = &PackageError{
-			ImportStack: stk.Copy(),
-			Err:         err,
+
+		setError(base.ExpandScanner(err))
+		if _, isScanErr := err.(scanner.ErrorList); !isScanErr {
+			return
 		}
-		return
+		// Fall through if there was an error parsing a file. 'go list -e' should
+		// still report imports and other metadata.
 	}
 
 	useBindir := p.Name == "main"
@@ -1545,7 +1559,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		if InstallTargetDir(p) == StalePath {
 			newPath := strings.Replace(p.ImportPath, "code.google.com/p/go.", "golang.org/x/", 1)
 			e := ImportErrorf(p.ImportPath, "the %v command has moved; use %v instead.", p.ImportPath, newPath)
-			p.Error = &PackageError{Err: e}
+			setError(e)
 			return
 		}
 		elem := p.DefaultExecName()
@@ -1658,10 +1672,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	inputs := p.AllFiles()
 	f1, f2 := str.FoldDup(inputs)
 	if f1 != "" {
-		p.Error = &PackageError{
-			ImportStack: stk.Copy(),
-			Err:         fmt.Errorf("case-insensitive file name collision: %q and %q", f1, f2),
-		}
+		setError(fmt.Errorf("case-insensitive file name collision: %q and %q", f1, f2))
 		return
 	}
 
@@ -1674,25 +1685,16 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	// so we shouldn't see any _cgo_ files anyway, but just be safe.
 	for _, file := range inputs {
 		if !SafeArg(file) || strings.HasPrefix(file, "_cgo_") {
-			p.Error = &PackageError{
-				ImportStack: stk.Copy(),
-				Err:         fmt.Errorf("invalid input file name %q", file),
-			}
+			setError(fmt.Errorf("invalid input file name %q", file))
 			return
 		}
 	}
 	if name := pathpkg.Base(p.ImportPath); !SafeArg(name) {
-		p.Error = &PackageError{
-			ImportStack: stk.Copy(),
-			Err:         fmt.Errorf("invalid input directory name %q", name),
-		}
+		setError(fmt.Errorf("invalid input directory name %q", name))
 		return
 	}
 	if !SafeArg(p.ImportPath) {
-		p.Error = &PackageError{
-			ImportStack: stk.Copy(),
-			Err:         ImportErrorf(p.ImportPath, "invalid import path %q", p.ImportPath),
-		}
+		setError(ImportErrorf(p.ImportPath, "invalid import path %q", p.ImportPath))
 		return
 	}
 
@@ -1737,13 +1739,6 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		// code; see issue #16050).
 	}
 
-	setError := func(err error) {
-		p.Error = &PackageError{
-			ImportStack: stk.Copy(),
-			Err:         err,
-		}
-	}
-
 	// The gc toolchain only permits C source files with cgo or SWIG.
 	if len(p.CFiles) > 0 && !p.UsesCgo() && !p.UsesSwig() && cfg.BuildContext.Compiler == "gc" {
 		setError(fmt.Errorf("C source files not allowed when not using cgo or SWIG: %s", strings.Join(p.CFiles, " ")))

src/cmd/go/testdata/script/list_parse_err.txt

+# 'go list' should report imports, even if some files have parse errors
+# before the import block.
+go list -e -f '{{range .Imports}}{{.}} {{end}}'
+stdout '^fmt '
+
+-- go.mod --
+module m
+
+go 1.13
+
+-- a.go --
+package a
+
+import "fmt"
+
+-- b.go --
+// no package statement

src/go/build/build.go

@@ -976,13 +976,6 @@ Found:
 		}
 	}
 
-	if badGoError != nil {
-		return p, badGoError
-	}
-	if len(p.GoFiles)+len(p.CgoFiles)+len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 {
-		return p, &NoGoError{p.Dir}
-	}
-
 	for tag := range allTags {
 		p.AllTags = append(p.AllTags, tag)
 	}
@@ -1000,6 +993,12 @@ Found:
 		sort.Strings(p.SFiles)
 	}
 
+	if badGoError != nil {
+		return p, badGoError
+	}
+	if len(p.GoFiles)+len(p.CgoFiles)+len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 {
+		return p, &NoGoError{p.Dir}
+	}
 	return p, pkgerr
 }