fix: report no timestamp when a task's sources match no file

CHANGELOG.md

@@ -24,6 +24,10 @@
   gets `{{.TIMESTAMP}}` and no longer a `{{.CHECKSUM}}` (which now renders as an
   empty string), and neither variable is injected when the effective method is
   `none` (#2924 by @vmaerten).
+- Fixed `{{.TIMESTAMP}}` rendering as the Unix epoch (e.g. `1970-01-01 01:00:00
+  +0100 CET`) when a task's `sources` matched no file. It now renders as an
+  empty string, instead of a date that looks genuine and carries the machine's
+  time zone (#2960 by @vmaerten).
 
 ## v3.52.0 - 2026-07-02
 

internal/fingerprint/sources_timestamp.go

@@ -122,8 +122,12 @@ func (checker *TimestampChecker) Value(t *ast.Task) (any, error) {
 		return time.Now(), err
 	}
 
+	// No source matched, so there is no modification time to report. Returning
+	// the Unix epoch here would render as a real date in templates, e.g.
+	// "1970-01-01 01:00:00 +0100 CET", which reads as a genuine timestamp and
+	// carries a machine-dependent zone.
 	if sourcesMaxTime.IsZero() {
-		return time.Unix(0, 0), nil
+		return "", nil
 	}
 
 	return sourcesMaxTime, nil

internal/fingerprint/sources_timestamp_test.go

@@ -0,0 +1,44 @@
+package fingerprint
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+func TestTimestampCheckerValue(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "source.txt"), []byte("content"), 0o644))
+	checker := NewTimestampChecker(t.TempDir(), true)
+
+	t.Run("reports the newest source modification time", func(t *testing.T) {
+		t.Parallel()
+
+		value, err := checker.Value(&ast.Task{
+			Dir:     dir,
+			Sources: []*ast.Glob{{Glob: "source.txt"}},
+		})
+		require.NoError(t, err)
+		assert.IsType(t, time.Time{}, value)
+		assert.False(t, value.(time.Time).IsZero())
+	})
+
+	t.Run("reports no value when no source matches", func(t *testing.T) {
+		t.Parallel()
+
+		value, err := checker.Value(&ast.Task{
+			Dir:     dir,
+			Sources: []*ast.Glob{{Glob: "gen/**/*.go"}},
+		})
+		require.NoError(t, err)
+		assert.Equal(t, "", value)
+	})
+}