refactor/importgraph: changes for vendor support

Each string in build.Package.{,Test,XTest}Imports must now be
interpreted relative to the Package.Dir.  This adds a ton of
redundant I/O.

Also:
- use a counting semaphore to limit concurrent I/O calls
  (Fixes golang/go#10306)
- remove obsolete call to runtime.GOMAXPROCS from the test.

Change-Id: Ic556c4cf41cce7a88c0158800c992e66f354c484
Reviewed-on: https://go-review.googlesource.com/18050
Reviewed-by: Russ Cox <rsc@golang.org>

refactor/importgraph/graph.go

@@ -53,9 +53,10 @@ func (g Graph) Search(roots ...string) map[string]bool {
 
 // Build scans the specified Go workspace and builds the forward and
 // reverse import dependency graphs for all its packages.
-// It also returns a mapping from import paths to errors for packages
+// It also returns a mapping from canonical import paths to errors for packages
 // whose loading was not entirely successful.
 // A package may appear in the graph and in the errors mapping.
+// All package paths are canonical and may contain "/vendor/".
 func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error) {
 	type importEdge struct {
 		from, to string
@@ -67,6 +68,7 @@ func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error
 
 	ch := make(chan interface{})
 
+	sema := make(chan int, 20) // I/O concurrency limiting semaphore
 	var wg sync.WaitGroup
 	buildutil.ForEachPackage(ctxt, func(path string, err error) {
 		wg.Add(1)
@@ -77,7 +79,10 @@ func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error
 				return
 			}
 
-			bp, err := ctxt.Import(path, "", 0)
+			sema <- 1
+			bp, err := ctxt.Import(path, "", buildutil.AllowVendor)
+			<-sema
+
 			if err != nil {
 				if _, ok := err.(*build.NoGoError); ok {
 					// empty directory is not an error
@@ -86,15 +91,43 @@ func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error
 				}
 				// Even in error cases, Import usually returns a package.
 			}
+
+			// absolutize resolves an import path relative
+			// to the current package bp.
+			// The absolute form may contain "vendor".
+			// TODO(adonovan): opt: experiment with
+			// overriding the IsDir method with a caching version
+			// to avoid a huge number of redundant I/O calls.
+			absolutize := func(path string) string { return path }
+			if buildutil.AllowVendor != 0 {
+				memo := make(map[string]string)
+				absolutize = func(path string) string {
+					canon, ok := memo[path]
+					if !ok {
+						sema <- 1
+						bp2, _ := ctxt.Import(path, bp.Dir, build.FindOnly|buildutil.AllowVendor)
+						<-sema
+
+						if bp2 != nil {
+							canon = bp2.ImportPath
+						} else {
+							canon = path
+						}
+						memo[path] = canon
+					}
+					return canon
+				}
+			}
+
 			if bp != nil {
 				for _, imp := range bp.Imports {
-					ch <- importEdge{path, imp}
+					ch <- importEdge{path, absolutize(imp)}
 				}
 				for _, imp := range bp.TestImports {
-					ch <- importEdge{path, imp}
+					ch <- importEdge{path, absolutize(imp)}
 				}
 				for _, imp := range bp.XTestImports {
-					ch <- importEdge{path, imp}
+					ch <- importEdge{path, absolutize(imp)}
 				}
 			}
 		}()

refactor/importgraph/graph_test.go

@@ -9,11 +9,13 @@
 package importgraph_test
 
 import (
+	"fmt"
 	"go/build"
-	"runtime"
 	"sort"
+	"strings"
 	"testing"
 
+	"golang.org/x/tools/go/buildutil"
 	"golang.org/x/tools/refactor/importgraph"
 
 	_ "crypto/hmac" // just for test, below
@@ -22,15 +24,12 @@ import (
 const this = "golang.org/x/tools/refactor/importgraph"
 
 func TestBuild(t *testing.T) {
-	saved := runtime.GOMAXPROCS(8) // Build is highly parallel
-	defer runtime.GOMAXPROCS(saved)
-
 	forward, reverse, errors := importgraph.Build(&build.Default)
 
 	// Test direct edges.
 	// We throw in crypto/hmac to prove that external test files
 	// (such as this one) are inspected.
-	for _, p := range []string{"go/build", "runtime", "testing", "crypto/hmac"} {
+	for _, p := range []string{"go/build", "testing", "crypto/hmac"} {
 		if !forward[this][p] {
 			t.Errorf("forward[importgraph][%s] not found", p)
 		}
@@ -40,7 +39,7 @@ func TestBuild(t *testing.T) {
 	}
 
 	// Test non-existent direct edges
-	for _, p := range []string{"fmt", "errors", "reflect"} {
+	for _, p := range []string{"errors", "reflect"} {
 		if forward[this][p] {
 			t.Errorf("unexpected: forward[importgraph][%s] found", p)
 		}
@@ -49,6 +48,14 @@ func TestBuild(t *testing.T) {
 		}
 	}
 
+	// Test vendor packages appear under their absolute names.
+	if buildutil.AllowVendor != 0 { // hack: Go 1.6+ only
+		if !forward["net/http"]["vendor/golang.org/x/net/http2/hpack"] {
+			t.Errorf("forward[net/http] does not include vendor/golang.org/x/net/http2/hpack: %v",
+				strings.Replace(fmt.Sprint(forward["net/http"]), ":true", "", -1))
+		}
+	}
+
 	// Test Search is reflexive.
 	if !forward.Search(this)[this] {
 		t.Errorf("irreflexive: forward.Search(importgraph)[importgraph] not found")