Adds Env to TaskRunSpec

Adds a `Env` field to `TaskRunSpec` to allow a user to set environment
variables on each step container. This mimics Knative-Build's
`TemplateInstantiationSpec`'s `Env` field.

Setting environment variables is useful for when a `TaskRun` author may
not know what variables are required ahead of time (e.g., Buildpacks).

fixes tektoncd#1606

pkg/apis/pipeline/v1alpha1/taskrun_types.go

@@ -48,9 +48,11 @@ type TaskRunSpec struct {
 	// Refer Go's ParseDuration documentation for expected format: https://golang.org/pkg/time/#ParseDuration
 	// +optional
 	Timeout *metav1.Duration `json:"timeout,omitempty"`
-
 	// PodTemplate holds pod specific configuration
 	PodTemplate PodTemplate `json:"podTemplate,omitempty"`
+	// Env, if specified will provide variables to all task steps.
+	// +optional
+	Env []corev1.EnvVar `json:"env,omitempty"`
 }
 
 // TaskRunSpecStatus defines the taskrun spec status the user can provide

pkg/pod/pod.go

@@ -144,10 +144,12 @@ func MakePod(images pipeline.Images, taskRun *v1alpha1.TaskRun, taskSpec v1alpha
 	}
 
 	// Add implicit env vars.
-	// They're prepended to the list, so that if the user specified any
-	// themselves their value takes precedence.
+	// Append to an empty list to ensure we don't alter implicitEnvVars.
+	// Precedence: step.Env > taskRun.Spec.Env > implicitEnvVars
 	for i, s := range stepContainers {
-		env := append(implicitEnvVars, s.Env...)
+		env := append([]corev1.EnvVar{}, implicitEnvVars...)
+		env = append(env, taskRun.Spec.Env...)
+		env = append(env, s.Env...)
 		stepContainers[i].Env = env
 	}
 

pkg/pod/pod_test.go

@@ -573,7 +573,55 @@ script-heredoc-randomly-generated-6nl7g
 			}},
 			Volumes: append(implicitVolumes, scriptsVolume, toolsVolume, downwardVolume),
 		},
-	}} {
+	}, {
+		desc: "env is set",
+		ts: v1alpha1.TaskSpec{
+			Steps: []v1alpha1.Step{{Container: corev1.Container{
+				Name:    "step-with-env",
+				Image:   "image",
+				Command: []string{"cmd"}, // avoid entrypoint lookup.
+			}}},
+		},
+		trs: v1alpha1.TaskRunSpec{
+			Env: []corev1.EnvVar{
+				{Name: "FOO", Value: "bar"},
+			},
+		},
+		want: &corev1.PodSpec{
+			RestartPolicy:  corev1.RestartPolicyNever,
+			InitContainers: []corev1.Container{placeToolsInit},
+			Containers: []corev1.Container{{
+				Name:    "step-step-with-env",
+				Image:   "image",
+				Command: []string{"/tekton/tools/entrypoint"},
+				Args: []string{
+					"-wait_file",
+					"/tekton/downward/ready",
+					"-wait_file_content",
+					"-post_file",
+					"/tekton/tools/0",
+					"-entrypoint",
+					"cmd",
+					"--",
+				},
+				// Append to an empty slice to avoid manipulating
+				// implicitEnvVars, but keep user variables last to ensure
+				// precedence.
+				Env:          append(append([]corev1.EnvVar{}, implicitEnvVars...), corev1.EnvVar{Name: "FOO", Value: "bar"}),
+				VolumeMounts: append([]corev1.VolumeMount{toolsMount, downwardMount}, implicitVolumeMounts...),
+				WorkingDir:   workspaceDir,
+				Resources: corev1.ResourceRequirements{
+					Requests: corev1.ResourceList{
+						corev1.ResourceCPU:              resource.MustParse("0"),
+						corev1.ResourceMemory:           resource.MustParse("0"),
+						corev1.ResourceEphemeralStorage: resource.MustParse("0"),
+					},
+				},
+			}},
+			Volumes: append(implicitVolumes, toolsVolume, downwardVolume),
+		},
+	},
+	} {
 		t.Run(c.desc, func(t *testing.T) {
 			names.TestingSeed()
 			kubeclient := fakek8s.NewSimpleClientset(