cmd/go: recognize android suffix when constructing build list

cmd/go/internal/imports.ScanDir extracts a list of imports from a
directory. It's used instead of go/build.ImportDir when constructing
the build list. GOOS and GOARCH may be used to filter files.

With this change, imports.MatchFile understands that when the
"android" tag is set, the "linux" tag is implied.

Fixes #30888

Change-Id: Ia29bd1590b69c9183ab14a879d5fc1b639f8eaef
Reviewed-on: https://go-review.googlesource.com/c/go/+/168378
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/imports/build.go

@@ -184,13 +184,13 @@ func MatchFile(name string, tags map[string]bool) bool {
 	}
 	n := len(l)
 	if n >= 2 && KnownOS[l[n-2]] && KnownArch[l[n-1]] {
-		return tags[l[n-2]] && tags[l[n-1]]
+		return matchTag(l[n-2], tags, true) && matchTag(l[n-1], tags, true)
 	}
 	if n >= 1 && KnownOS[l[n-1]] {
-		return tags[l[n-1]]
+		return matchTag(l[n-1], tags, true)
 	}
 	if n >= 1 && KnownArch[l[n-1]] {
-		return tags[l[n-1]]
+		return matchTag(l[n-1], tags, true)
 	}
 	return true
 }

src/cmd/go/internal/imports/scan_test.go

@@ -5,10 +5,13 @@
 package imports
 
 import (
+	"bytes"
 	"internal/testenv"
+	"io/ioutil"
+	"path"
 	"path/filepath"
-	"reflect"
 	"runtime"
+	"strings"
 	"testing"
 )
 
@@ -51,17 +54,41 @@ func TestScan(t *testing.T) {
 		t.Errorf("json missing test import net/http (%q)", testImports)
 	}
 }
-
-func TestScanStar(t *testing.T) {
+func TestScanDir(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 
-	imports, _, err := ScanDir("testdata/import1", map[string]bool{"*": true})
+	dirs, err := ioutil.ReadDir("testdata")
 	if err != nil {
 		t.Fatal(err)
 	}
+	for _, dir := range dirs {
+		if !dir.IsDir() || strings.HasPrefix(dir.Name(), ".") {
+			continue
+		}
+		t.Run(dir.Name(), func(t *testing.T) {
+			tagsData, err := ioutil.ReadFile(filepath.Join("testdata", dir.Name(), "tags.txt"))
+			if err != nil {
+				t.Fatalf("error reading tags: %v", err)
+			}
+			tags := make(map[string]bool)
+			for _, t := range strings.Fields(string(tagsData)) {
+				tags[t] = true
+			}
+
+			wantData, err := ioutil.ReadFile(filepath.Join("testdata", dir.Name(), "want.txt"))
+			if err != nil {
+				t.Fatalf("error reading want: %v", err)
+			}
+			want := string(bytes.TrimSpace(wantData))
 
-	want := []string{"import1", "import2", "import3", "import4"}
-	if !reflect.DeepEqual(imports, want) {
-		t.Errorf("ScanDir testdata/import1:\nhave %v\nwant %v", imports, want)
+			imports, _, err := ScanDir(path.Join("testdata", dir.Name()), tags)
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := strings.Join(imports, "\n")
+			if got != want {
+				t.Errorf("ScanDir: got imports:\n%s\n\nwant:\n%s", got, want)
+			}
+		})
 	}
 }

src/cmd/go/internal/imports/testdata/android/a_android.go

+package android
+
+import _ "a"

src/cmd/go/internal/imports/testdata/android/b_android_arm64.go

+package android
+
+import _ "b"

src/cmd/go/internal/imports/testdata/android/c_linux.go

+package android
+
+import _ "c"

src/cmd/go/internal/imports/testdata/android/d_linux_arm64.go

+package android
+
+import _ "d"

src/cmd/go/internal/imports/testdata/android/e.go

+// +build android
+
+package android
+
+import _ "e"

src/cmd/go/internal/imports/testdata/android/f.go

+// +build linux
+
+package android
+
+import _ "f"

src/cmd/go/internal/imports/testdata/android/g.go

+// +build !android
+
+package android
+
+import _ "g"

src/cmd/go/internal/imports/testdata/android/tags.txt

+android arm64
\ No newline at end of file

src/cmd/go/internal/imports/testdata/android/want.txt

+a
+b
+c
+d
+e
+f

src/cmd/go/internal/imports/testdata/star/tags.txt

+*
\ No newline at end of file

src/cmd/go/internal/imports/testdata/star/want.txt

+import1
+import2
+import3
+import4