validation: don't strip marks from variables during validation

.changes/v1.13/BUG FIXES-20250911-142038.yaml

@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: 'variable validation: keep sensitive and ephemeral metadata when evaluating variable conditions.'
+time: 2025-09-11T14:20:38.411183+02:00
+custom:
+    Issue: "37595"

internal/terraform/context_plan_test.go

@@ -6974,7 +6974,7 @@ func TestContext2Plan_variableCustomValidationsCrossRef(t *testing.T) {
 	}
 }
 
-func TestContext2Plan_variableCustomValidationsSensitive(t *testing.T) {
+func TestContext2Plan_variableCustomValidationsChildSensitive(t *testing.T) {
 	m := testModule(t, "validate-variable-custom-validations-child-sensitive")
 
 	p := testProvider("test")
@@ -6993,6 +6993,39 @@ func TestContext2Plan_variableCustomValidationsSensitive(t *testing.T) {
 	}
 }
 
+func TestContext2Plan_variableCustomValidationsSensitive(t *testing.T) {
+	m := testModule(t, "validate-variable-custom-validations-sensitive")
+
+	p := testProvider("test")
+	ctx := testContext2(t, &ContextOpts{
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("test"): testProviderFuncFixed(p),
+		},
+	})
+
+	_, diags := ctx.Plan(m, states.NewState(), SimplePlanOpts(plans.NormalMode, InputValues{
+		"input": {
+			Value: cty.StringVal("short"),
+		},
+	}))
+	if len(diags) != 1 {
+		t.Fatal("wanted exactly one error")
+	}
+	if diff := cmp.Diff(diags[0].Description(), tfdiags.Description{
+		Summary: "Invalid value for variable",
+		Detail:  "too short\n\nThis was checked by the validation rule at testdata/validate-variable-custom-validations-sensitive/validate-variable-custom-validations-sensitive.tf:4,3-13.",
+	}); len(diff) > 0 {
+		t.Error(diff)
+	}
+
+	vars := diags[0].FromExpr().EvalContext.Variables["var"].AsValueMap()
+
+	_, ms := vars["input"].Unmark()
+	if _, ok := ms[marks.Sensitive]; !ok {
+		t.Error("should have been marked as sensitive")
+	}
+}
+
 func TestContext2Plan_nullOutputNoOp(t *testing.T) {
 	// this should always plan a NoOp change for the output
 	m := testModuleInline(t, map[string]string{

internal/terraform/eval_variable.go

@@ -281,31 +281,33 @@ func evalVariableValidations(addr addrs.AbsInputVariableInstance, ctx EvalContex
 	// Although that behavior was accidental, it makes simple validation rules
 	// more useful and is protected by compatibility promises, and so we'll
 	// fake it here by overwriting the unknown value that scope.EvalContext
-	// will have inserted with a possibly-more-known value using the same
-	// strategy our special code used to use.
-	ourVal := ctx.NamedValues().GetInputVariableValue(addr)
-	if ourVal != cty.NilVal {
-		// (it would be weird for ourVal to be nil here, but we'll tolerate it
-		// because it was scope.EvalContext's responsibility to check for the
-		// absent final value, and even if it didn't we'll just get an
-		// evaluation error when evaluating the expressions below anyway.)
-
-		// Our goal here is to make sure that a reference to the variable
-		// we're checking will evaluate to ourVal, regardless of what else
-		// scope.EvalContext might have put in the variables table.
-		if hclCtx.Variables == nil {
-			hclCtx.Variables = make(map[string]cty.Value)
-		}
-		if varsVal, ok := hclCtx.Variables["var"]; ok {
-			// Unfortunately we need to unpack and repack the object here,
-			// because cty values are immutable.
-			attrs := varsVal.AsValueMap()
-			attrs[addr.Variable.Name] = ourVal
-			hclCtx.Variables["var"] = cty.ObjectVal(attrs)
-		} else {
-			hclCtx.Variables["var"] = cty.ObjectVal(map[string]cty.Value{
-				addr.Variable.Name: ourVal,
-			})
+	// will have inserted during validate walks with a possibly-more-known value
+	// using the same strategy our special code used to use.
+	if validateWalk {
+		ourVal := ctx.NamedValues().GetInputVariableValue(addr)
+		if ourVal != cty.NilVal {
+			// (it would be weird for ourVal to be nil here, but we'll tolerate it
+			// because it was scope.EvalContext's responsibility to check for the
+			// absent final value, and even if it didn't we'll just get an
+			// evaluation error when evaluating the expressions below anyway.)
+
+			// Our goal here is to make sure that a reference to the variable
+			// we're checking will evaluate to ourVal, regardless of what else
+			// scope.EvalContext might have put in the variables table.
+			if hclCtx.Variables == nil {
+				hclCtx.Variables = make(map[string]cty.Value)
+			}
+			if varsVal, ok := hclCtx.Variables["var"]; ok {
+				// Unfortunately we need to unpack and repack the object here,
+				// because cty values are immutable.
+				attrs := varsVal.AsValueMap()
+				attrs[addr.Variable.Name] = ourVal
+				hclCtx.Variables["var"] = cty.ObjectVal(attrs)
+			} else {
+				hclCtx.Variables["var"] = cty.ObjectVal(map[string]cty.Value{
+					addr.Variable.Name: ourVal,
+				})
+			}
 		}
 	}
 

internal/terraform/testdata/validate-variable-custom-validations-sensitive/validate-variable-custom-validations-sensitive.tf

@@ -0,0 +1,13 @@
+
+variable "input" {
+  type = string
+  validation {
+    condition = length(var.input) > 5
+    error_message = "too short"
+  }
+  sensitive = true
+}
+
+output "value" {
+  value = var.input
+}