extract: new package to extract symbols from a dependency

cmd/goexports is now based on it.

Updates #639 

Co-authored-by: Marc Vertes <mvertes@free.fr>

extract/extract_test.go

@@ -0,0 +1,140 @@
+package extract
+
+import (
+	"bytes"
+	"os"
+	"path"
+	"strings"
+	"testing"
+)
+
+var expectedOutput = `// Code generated by 'github.com/containous/yaegi/extract guthib.com/baz'. DO NOT EDIT.
+
+// +build BUILD_TAGS
+
+package bar
+
+import (
+	"guthib.com/baz"
+	"reflect"
+)
+
+func init() {
+	Symbols["guthib.com/baz"] = map[string]reflect.Value{
+		// function, constant and variable definitions
+		"Hello": reflect.ValueOf(baz.Hello),
+	}
+}
+`
+
+func init() {
+	buildTags, err := buildTags()
+	if err != nil {
+		panic(err)
+	}
+	expectedOutput = strings.Replace(expectedOutput, "BUILD_TAGS", buildTags, 1)
+}
+
+func TestPackages(t *testing.T) {
+	testCases := []struct {
+		desc       string
+		moduleOn   string
+		wd         string
+		arg        string
+		importPath string
+		expected   string
+		contains   string
+		dest       string
+	}{
+		{
+			desc: "stdlib math pkg, using go/importer",
+			dest: "math",
+			arg:  "math",
+			// We check this one because it shows both defects when we break it: the value
+			// gets corrupted, and the type becomes token.INT
+			// TODO(mpl): if the ident between key and value becomes annoying, be smarter about it.
+			contains: `"MaxFloat64":             reflect.ValueOf(constant.MakeFromLiteral("179769313486231570814527423731704356798100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", token.FLOAT, 0)),`,
+		},
+		{
+			desc:     "using relative path, using go.mod",
+			wd:       "./testdata/1/src/guthib.com/bar",
+			arg:      "../baz",
+			expected: expectedOutput,
+		},
+		{
+			desc:       "using relative path, manual import path",
+			wd:         "./testdata/2/src/guthib.com/bar",
+			arg:        "../baz",
+			importPath: "guthib.com/baz",
+			expected:   expectedOutput,
+		},
+		{
+			desc:       "using relative path, go.mod is ignored, because manual path",
+			wd:         "./testdata/3/src/guthib.com/bar",
+			arg:        "../baz",
+			importPath: "guthib.com/baz",
+			expected:   expectedOutput,
+		},
+		{
+			desc:     "using relative path, dep in vendor, using go.mod",
+			wd:       "./testdata/4/src/guthib.com/bar",
+			arg:      "./vendor/guthib.com/baz",
+			expected: expectedOutput,
+		},
+		{
+			desc:       "using relative path, dep in vendor, manual import path",
+			wd:         "./testdata/5/src/guthib.com/bar",
+			arg:        "./vendor/guthib.com/baz",
+			importPath: "guthib.com/baz",
+			expected:   expectedOutput,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			cwd, err := os.Getwd()
+			if err != nil {
+				t.Fatal(err)
+			}
+			wd := test.wd
+			if wd == "" {
+				wd = cwd
+			} else {
+				if err := os.Chdir(wd); err != nil {
+					t.Fatal(err)
+				}
+				defer func() {
+					if err := os.Chdir(cwd); err != nil {
+						t.Fatal(err)
+					}
+				}()
+			}
+
+			dest := path.Base(wd)
+			if test.dest != "" {
+				dest = test.dest
+			}
+			ext := Extractor{
+				Dest: dest,
+			}
+
+			var out bytes.Buffer
+			if _, err := ext.Extract(test.arg, test.importPath, &out); err != nil {
+				t.Fatal(err)
+			}
+
+			if test.expected != "" {
+				if out.String() != test.expected {
+					t.Fatalf("\nGot:\n%q\nWant: \n%q", out.String(), test.expected)
+				}
+			}
+
+			if test.contains != "" {
+				if !strings.Contains(out.String(), test.contains) {
+					t.Fatalf("Missing expected part: %s in %s", test.contains, out.String())
+				}
+			}
+		})
+	}
+}