Backport of Fix panic for invalid `action_trigger` nested blocks in `data` and `ephemeral` into v1.15 (#38452)

* backport of commit e65b690f80

* backport of commit f69f06a1ff

---------

Co-authored-by: Austin Valle <austinvalle@gmail.com>

.changes/v1.15/BUG FIXES-20260427-092612.yaml

@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: Fixed crash when configuration has an invalid `action_trigger` nested block in `data` or `ephemeral` lifecycle blocks
+time: 2026-04-27T09:26:12.662049-04:00
+custom:
+    Issue: "38402"

internal/configs/resource.go

@@ -509,6 +509,13 @@ func decodeEphemeralBlock(block *hcl.Block, override bool) (*Resource, hcl.Diagn
 					case "postcondition":
 						r.Postconditions = append(r.Postconditions, cr)
 					}
+				case "action_trigger":
+					diags = append(diags, &hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Invalid ephemeral resource lifecycle nested block",
+						Detail:   fmt.Sprintf("The lifecycle nested block %q is defined only for managed resources (\"resource\" blocks), and is not valid for ephemeral resources.", block.Type),
+						Subject:  block.TypeRange.Ptr(),
+					})
 				default:
 					// The cases above should be exhaustive for all block types
 					// defined in the lifecycle schema, so this shouldn't happen.
@@ -685,6 +692,13 @@ func decodeDataBlock(block *hcl.Block, override, nested bool) (*Resource, hcl.Di
 					case "postcondition":
 						r.Postconditions = append(r.Postconditions, cr)
 					}
+				case "action_trigger":
+					diags = append(diags, &hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Invalid data resource lifecycle nested block",
+						Detail:   fmt.Sprintf("The lifecycle nested block %q is defined only for managed resources (\"resource\" blocks), and is not valid for data resources.", block.Type),
+						Subject:  block.TypeRange.Ptr(),
+					})
 				default:
 					// The cases above should be exhaustive for all block types
 					// defined in the lifecycle schema, so this shouldn't happen.

internal/configs/testdata/invalid-files/data-invalid-action-trigger.tf

@@ -0,0 +1,10 @@
+action "test_action" "test" {}
+
+data "test_data" "test" {
+  lifecycle {
+    action_trigger {
+      actions = [action.test_action.test]
+      events  = [after_create, after_update]
+    }
+  }
+}

internal/configs/testdata/invalid-files/ephemeral-invalid-action_trigger.tf

@@ -0,0 +1,10 @@
+action "test_action" "test" {}
+
+ephemeral "test_ephemeral" "test" {
+  lifecycle {
+    action_trigger {
+      actions = [action.test_action.test]
+      events  = [after_create, after_update]
+    }
+  }
+}