Add `type` attribute to `output` blocks

internal/configs/named_values.go

@@ -388,12 +388,24 @@ type Output struct {
 	Ephemeral   bool
 	Deprecated  string
 
+	// ConstraintType is a type constraint which the result is guaranteed
+	// to conform to when used in the calling module.
+	ConstraintType cty.Type
+	// TypeDefaults describes any optional attribute defaults that should be
+	// applied to the Expr result before type conversion.
+	TypeDefaults *typeexpr.Defaults
+
 	Preconditions []*CheckRule
 
 	DescriptionSet bool
 	SensitiveSet   bool
 	EphemeralSet   bool
 	DeprecatedSet  bool
+	// TypeSet is true if there was an explicit "type" argument in the
+	// configuration block. This is mainly to allow distinguish explicitly
+	// setting vs. just using the default type constraint when processing
+	// override files.
+	TypeSet bool
 
 	DeclRange       hcl.Range
 	DeprecatedRange hcl.Range
@@ -434,6 +446,19 @@ func decodeOutputBlock(block *hcl.Block, override bool) (*Output, hcl.Diagnostic
 		o.Expr = attr.Expr
 	}
 
+	if attr, exists := content.Attributes["type"]; exists {
+		ty, defaults, moreDiags := typeexpr.TypeConstraintWithDefaults(attr.Expr)
+		diags = append(diags, moreDiags...)
+		o.ConstraintType = ty
+		o.TypeDefaults = defaults
+		o.TypeSet = true
+	}
+	if o.ConstraintType == cty.NilType {
+		// If no constraint is given then the type will be inferred
+		// automatically from the value.
+		o.ConstraintType = cty.DynamicPseudoType
+	}
+
 	if attr, exists := content.Attributes["sensitive"]; exists {
 		valDiags := gohcl.DecodeExpression(attr.Expr, nil, &o.Sensitive)
 		diags = append(diags, valDiags...)
@@ -587,6 +612,9 @@ var outputBlockSchema = &hcl.BodySchema{
 		{
 			Name: "deprecated",
 		},
+		{
+			Name: "type",
+		},
 	},
 	Blocks: []hcl.BlockHeaderSchema{
 		{Type: "precondition"},

internal/configs/testdata/valid-files/output-type-constraint.tf

@@ -0,0 +1,11 @@
+output "string" {
+  type  = string
+  value = "Hello"
+}
+
+output "object" {
+  type = object({
+    name = optional(string, "Bart"),
+  })
+  value = {}
+}