feat(bigquery): allow construction of jobs from other projects (#5048)

Adds a `JobfromProject()` method to allow users to get metadata from a
job that was created within another project.

Fixes: #4228

Author: shollyman

Diff for: bigquery/integration_test.go

@@ -250,6 +250,70 @@ func TestIntegration_DetectProjectID(t *testing.T) {
 	}
 }
 
+func TestIntegration_JobFrom(t *testing.T) {
+	if client == nil {
+		t.Skip("Integration tests skipped")
+	}
+	ctx := context.Background()
+
+	// Create a job we can use for referencing.
+	q := client.Query("SELECT 123 as foo")
+	it, err := q.Read(ctx)
+	if err != nil {
+		t.Fatalf("failed to run test query: %v", err)
+	}
+	want := it.SourceJob()
+
+	// establish a new client that's pointed at an invalid project/location.
+	otherClient, err := NewClient(ctx, "bad-project-id")
+	if err != nil {
+		t.Fatalf("failed to create other client: %v", err)
+	}
+	otherClient.Location = "badloc"
+
+	for _, tc := range []struct {
+		description string
+		f           func(*Client) (*Job, error)
+		wantErr     bool
+	}{
+		{
+			description: "JobFromID",
+			f:           func(c *Client) (*Job, error) { return c.JobFromID(ctx, want.jobID) },
+			wantErr:     true,
+		},
+		{
+			description: "JobFromIDLocation",
+			f:           func(c *Client) (*Job, error) { return c.JobFromIDLocation(ctx, want.jobID, want.location) },
+			wantErr:     true,
+		},
+		{
+			description: "JobFromProject",
+			f:           func(c *Client) (*Job, error) { return c.JobFromProject(ctx, want.projectID, want.jobID, want.location) },
+		},
+	} {
+		got, err := tc.f(otherClient)
+		if err != nil {
+			if !tc.wantErr {
+				t.Errorf("case %q errored: %v", tc.description, err)
+			}
+			continue
+		}
+		if tc.wantErr {
+			t.Errorf("case %q got success, expected error", tc.description)
+		}
+		if got.projectID != want.projectID {
+			t.Errorf("case %q projectID mismatch, got %s want %s", tc.description, got.projectID, want.projectID)
+		}
+		if got.location != want.location {
+			t.Errorf("case %q location mismatch, got %s want %s", tc.description, got.location, want.location)
+		}
+		if got.jobID != want.jobID {
+			t.Errorf("case %q jobID mismatch, got %s want %s", tc.description, got.jobID, want.jobID)
+		}
+	}
+
+}
+
 func TestIntegration_TableCreate(t *testing.T) {
 	// Check that creating a record field with an empty schema is an error.
 	if client == nil {

Diff for: bigquery/job.go

@@ -46,17 +46,24 @@ type Job struct {
 // For jobs whose location is other than "US" or "EU", set Client.Location or use
 // JobFromIDLocation.
 func (c *Client) JobFromID(ctx context.Context, id string) (*Job, error) {
-	return c.JobFromIDLocation(ctx, id, c.Location)
+	return c.JobFromProject(ctx, c.projectID, id, c.Location)
 }
 
 // JobFromIDLocation creates a Job which refers to an existing BigQuery job. The job
 // need not have been created by this package (for example, it may have
 // been created in the BigQuery console), but it must exist in the specified location.
 func (c *Client) JobFromIDLocation(ctx context.Context, id, location string) (j *Job, err error) {
-	ctx = trace.StartSpan(ctx, "cloud.google.com/go/bigquery.JobFromIDLocation")
+	return c.JobFromProject(ctx, c.projectID, id, location)
+}
+
+// JobFromProject creates a Job which refers to an existing BigQuery job.  The job
+// need not have been created by this package, nor does it need to reside within the same
+// project or location as the instantiated client.
+func (c *Client) JobFromProject(ctx context.Context, projectID, jobID, location string) (j *Job, err error) {
+	ctx = trace.StartSpan(ctx, "cloud.google.com/go/bigquery.JobFromProject")
 	defer func() { trace.EndSpan(ctx, err) }()
 
-	bqjob, err := c.getJobInternal(ctx, id, location, "configuration", "jobReference", "status", "statistics")
+	bqjob, err := c.getJobInternal(ctx, jobID, location, projectID, "configuration", "jobReference", "status", "statistics")
 	if err != nil {
 		return nil, err
 	}
@@ -799,9 +806,13 @@ func convertListedJob(j *bq.JobListJobs, c *Client) (*Job, error) {
 	return bqToJob2(j.JobReference, j.Configuration, j.Status, j.Statistics, j.UserEmail, c)
 }
 
-func (c *Client) getJobInternal(ctx context.Context, jobID, location string, fields ...googleapi.Field) (*bq.Job, error) {
+func (c *Client) getJobInternal(ctx context.Context, jobID, location, projectID string, fields ...googleapi.Field) (*bq.Job, error) {
 	var job *bq.Job
-	call := c.bqs.Jobs.Get(c.projectID, jobID).Context(ctx)
+	proj := projectID
+	if proj == "" {
+		proj = c.projectID
+	}
+	call := c.bqs.Jobs.Get(proj, jobID).Context(ctx)
 	if location != "" {
 		call = call.Location(location)
 	}