Handle vendor packages

tools/please_go/ChangeLog

@@ -1,3 +1,7 @@
+Version 1.10.6
+--------------
+    * packageinfo files correctly account for stdlib vendoring
+
 Version 1.10.5
 --------------
     * upgrade x/mod to support new directives

tools/please_go/VERSION

@@ -1 +1 @@
-1.10.5
+1.10.6

tools/please_go/packageinfo/packageinfo.go

@@ -88,6 +88,20 @@ func WritePackageInfo(importPath string, srcRoot, importconfig string, imports m
 			return !present
 		})
 	}
+	// Vendor packages. They aren't identified by the original imports but we know what they are now.
+	vendorised := map[string]*packages.Package{}
+	for _, pkg := range pkgs {
+		if strings.HasPrefix(pkg.PkgPath, "vendor/") {
+			vendorised[strings.TrimPrefix(pkg.PkgPath, "vendor/")] = pkg
+		}
+	}
+	for _, pkg := range pkgs {
+		for k := range pkg.Imports {
+			if v, present := vendorised[k]; present {
+				pkg.Imports[k] = v
+			}
+		}
+	}
 	// Ensure output is deterministic
 	sort.Slice(pkgs, func(i, j int) bool {
 		return pkgs[i].ID < pkgs[j].ID