Adding substitution for result path variable

docs/developers/README.md

@@ -275,3 +275,5 @@ status:
     value: |
       1579722445
 ```
+
+Instead of hardcoding the path to the result file, the user can also use a variable. So `/tekton/results/current-date-unix-timestamp` can be replaced with: `$(results.current-date-unix-timestamp.path)`. This is more flexible if the path to result files ever changes.

pkg/reconciler/taskrun/resources/apply.go

@@ -18,9 +18,11 @@ package resources
 
 import (
 	"fmt"
+	"path/filepath"
 
 	"github.com/tektoncd/pipeline/pkg/workspace"
 
+	"github.com/tektoncd/pipeline/pkg/apis/pipeline"
 	"github.com/tektoncd/pipeline/pkg/apis/pipeline/v1alpha1"
 	"github.com/tektoncd/pipeline/pkg/substitution"
 )
@@ -96,6 +98,17 @@ func ApplyWorkspaces(spec *v1alpha1.TaskSpec, w []v1alpha1.WorkspaceDeclaration,
 	return ApplyReplacements(spec, stringReplacements, map[string][]string{})
 }
 
+// ApplyTaskResults applies the substitution from values in results which are referenced in spec as subitems
+// of the replacementStr.
+func ApplyTaskResults(spec *v1alpha1.TaskSpec) *v1alpha1.TaskSpec {
+	stringReplacements := map[string]string{}
+
+	for _, result := range spec.Results {
+		stringReplacements[fmt.Sprintf("results.%s.path", result.Name)] = filepath.Join(pipeline.DefaultResultPath, result.Name)
+	}
+	return ApplyReplacements(spec, stringReplacements, map[string][]string{})
+}
+
 // ApplyReplacements replaces placeholders for declared parameters with the specified replacements.
 func ApplyReplacements(spec *v1alpha1.TaskSpec, stringReplacements map[string]string, arrayReplacements map[string][]string) *v1alpha1.TaskSpec {
 	spec = spec.DeepCopy()

pkg/reconciler/taskrun/resources/apply_test.go

@@ -720,6 +720,42 @@ func TestApplyWorkspaces(t *testing.T) {
 	}}
 	got := resources.ApplyWorkspaces(ts, w, wb)
 	if d := cmp.Diff(got, want); d != "" {
-		t.Errorf("ApplyParameters() got diff %s", d)
+		t.Errorf("TestApplyWorkspaces() got diff %s", d)
+	}
+}
+
+func TestTaskResults(t *testing.T) {
+	names.TestingSeed()
+	ts := &v1alpha1.TaskSpec{
+		Results: []v1alpha1.TaskResult{{
+			Name:        "current-date-unix-timestamp",
+			Description: "The current date in unix timestamp format",
+		}, {
+			Name:        "current-date-human-readable",
+			Description: "The current date in humand readable format"},
+		},
+		Steps: []v1alpha1.Step{{
+			Container: corev1.Container{
+				Name:  "print-date-unix-timestamp",
+				Image: "bash:latest",
+				Args:  []string{"$(results.current-date-unix-timestamp.path)"},
+			},
+			Script: "#!/usr/bin/env bash\ndate +%s | tee $(results.current-date-unix-timestamp.path)",
+		}, {
+			Container: corev1.Container{
+				Name:  "print-date-humman-readable",
+				Image: "bash:latest",
+			},
+			Script: "#!/usr/bin/env bash\ndate | tee $(results.current-date-human-readable.path)",
+		}},
+	}
+	want := applyMutation(ts, func(spec *v1alpha1.TaskSpec) {
+		spec.Steps[0].Script = "#!/usr/bin/env bash\ndate +%s | tee /tekton/results/current-date-unix-timestamp"
+		spec.Steps[0].Args[0] = "/tekton/results/current-date-unix-timestamp"
+		spec.Steps[1].Script = "#!/usr/bin/env bash\ndate | tee /tekton/results/current-date-human-readable"
+	})
+	got := resources.ApplyTaskResults(ts)
+	if d := cmp.Diff(got, want); d != "" {
+		t.Errorf("ApplyTaskResults() got diff %s", d)
 	}
 }

pkg/reconciler/taskrun/taskrun.go

@@ -513,6 +513,9 @@ func (c *Reconciler) createPod(tr *v1alpha1.TaskRun, rtr *resources.ResolvedTask
 	// Apply workspace resource substitution
 	ts = resources.ApplyWorkspaces(ts, ts.Workspaces, tr.Spec.Workspaces)
 
+	// Apply task result substitution
+	ts = resources.ApplyTaskResults(ts)
+
 	ts, err = workspace.Apply(*ts, tr.Spec.Workspaces)
 	if err != nil {
 		c.Logger.Errorf("Failed to create a pod for taskrun: %s due to workspace error %v", tr.Name, err)