accept empty default values

Author: Emyrk

extract/parameter.go

@@ -50,7 +50,7 @@ func ParameterFromBlock(block *terraform.Block) (*types.Parameter, hcl.Diagnosti
 
 	pVal := richParameterValue(block)
 
-	def := types.StringLiteral("")
+	def := types.NullString()
 	defAttr := block.GetAttribute("default")
 	if !defAttr.IsNil() {
 		def = types.ToHCLString(block, defAttr)
@@ -138,45 +138,10 @@ func ParameterFromBlock(block *terraform.Block) (*types.Parameter, hcl.Diagnosti
 		p.Validations = append(p.Validations, &valid)
 	}
 
-	ctyType, err := p.CtyType()
-	if err != nil {
-		paramTypeDiag := &hcl.Diagnostic{
-			Severity: hcl.DiagError,
-			Summary:  fmt.Sprintf("Invalid parameter type %q", p.Type),
-			Detail:   err.Error(),
-			Context:  &block.HCLBlock().DefRange,
-		}
-
-		if attr := block.GetAttribute("type"); attr != nil && !attr.IsNil() {
-			paramTypeDiag.Subject = &attr.HCLAttribute().Range
-			paramTypeDiag.Expression = attr.HCLAttribute().Expr
-			paramTypeDiag.EvalContext = block.Context().Inner()
-		}
-		diags = diags.Append(paramTypeDiag)
-		p.FormType = provider.ParameterFormTypeError
-	}
-
-	if ctyType != cty.NilType && pVal.Value.Type().Equals(cty.String) {
-		// TODO: Wish we could support more types, but only string types are
-		// allowed.
-		valStr := pVal.Value.AsString()
-		// Apply validations to the parameter value
-		for _, v := range p.Validations {
-			if err := v.Valid(string(pType), valStr); err != nil {
-				diags = diags.Append(&hcl.Diagnostic{
-					Severity:   hcl.DiagError,
-					Summary:    fmt.Sprintf("Paramater validation failed for value %q", valStr),
-					Detail:     err.Error(),
-					Expression: pVal.ValueExpr,
-				})
-			}
-		}
-	}
-
 	if !diags.HasErrors() {
 		// Only do this validation if the parameter is valid, as if some errors
 		// exist, then this is likely to fail be excess information.
-		diags = diags.Extend(p.Valid())
+		diags = diags.Extend(p.Valid(p.Value))
 	}
 
 	usageDiags := ParameterUsageDiagnostics(p)
@@ -194,7 +159,9 @@ func ParameterFromBlock(block *terraform.Block) (*types.Parameter, hcl.Diagnosti
 func ParameterUsageDiagnostics(p types.Parameter) hcl.Diagnostics {
 	valErr := "The value of a parameter is required to be sourced (default or input) for the parameter to function."
 	var diags hcl.Diagnostics
-	if !p.Value.Valid() {
+	if p.Value.Value.IsNull() {
+		// Allow null values
+	} else if !p.Value.Valid() {
 		diags = diags.Append(&hcl.Diagnostic{
 			Severity:   hcl.DiagError,
 			Summary:    "Parameter value is not valid",
@@ -478,6 +445,14 @@ func richParameterValue(block *terraform.Block) types.HCLString {
 
 	val, diags := valRef.Value(block.Context().Inner())
 	source := hclext.CreateDotReferenceFromTraversal(valRef.Traversal)
+
+	// If no value attribute exists, then the value is `null`.
+	if diags.HasErrors() && diags[0].Summary == "Unsupported attribute" {
+		s := types.NullString()
+		s.Source = &source
+		return s
+	}
+
 	return types.HCLString{
 		Value:      val,
 		ValueDiags: diags,

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/aquasecurity/trivy v0.58.2
 	github.com/coder/guts v1.0.2-0.20250227211802-139809366a22
 	github.com/coder/serpent v0.10.0
-	github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250502142605-22f12cb73817
+	github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250505161541-0fd96eeace73
 	github.com/coder/websocket v1.8.13
 	github.com/go-chi/chi v4.1.2+incompatible
 	github.com/hashicorp/go-cty v1.4.1-0.20200414143053-d3edf31b6320

go.sum

@@ -718,8 +718,8 @@ github.com/coder/pretty v0.0.0-20230908205945-e89ba86370e0 h1:3A0ES21Ke+FxEM8CXx
 github.com/coder/pretty v0.0.0-20230908205945-e89ba86370e0/go.mod h1:5UuS2Ts+nTToAMeOjNlnHFkPahrtDkmpydBen/3wgZc=
 github.com/coder/serpent v0.10.0 h1:ofVk9FJXSek+SmL3yVE3GoArP83M+1tX+H7S4t8BSuM=
 github.com/coder/serpent v0.10.0/go.mod h1:cZFW6/fP+kE9nd/oRkEHJpG6sXCtQ+AX7WMMEHv0Y3Q=
-github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250502142605-22f12cb73817 h1:4ryzTbgCe+AHk/G03y48Rtg3Y+pfr5FfhGt/eEckJ6g=
-github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250502142605-22f12cb73817/go.mod h1:56/KdGYaA+VbwXJbTI8CA57XPfnuTxN8rjxbR34PbZw=
+github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250505161541-0fd96eeace73 h1:Gax/pSsln9cSTueP5teoWM4EPqEux4BUp7VlECiuW2M=
+github.com/coder/terraform-provider-coder/v2 v2.4.0-pre1.0.20250505161541-0fd96eeace73/go.mod h1:2kaBpn5k9ZWtgKq5k4JbkVZG9DzEqR4mJSmpdshcO+s=
 github.com/coder/websocket v1.8.13 h1:f3QZdXy7uGVz+4uCJy2nTZyM0yTBj8yANEHhqlXZ9FE=
 github.com/coder/websocket v1.8.13/go.mod h1:LNVeNrXQZfe5qhS9ALED3uA+l5pPqvwXg3CKoDBB2gs=
 github.com/containerd/log v0.1.0 h1:TCJt7ioM2cr/tfR8GPbGf9/VRAX8D2B4PjzCpfX540I=

preview_test.go

@@ -211,6 +211,16 @@ func Test_Extract(t *testing.T) {
 			unknownTags: []string{},
 			params:      map[string]assertParam{},
 		},
+		{
+			name:        "empty default",
+			dir:         "emptydefault",
+			expTags:     map[string]string{},
+			input:       preview.Input{},
+			unknownTags: []string{},
+			params: map[string]assertParam{
+				"word": ap(),
+			},
+		},
 		{
 			name:    "many modules",
 			dir:     "manymodules",

testdata/emptydefault/main.tf

@@ -0,0 +1,26 @@
+terraform {
+  required_providers {
+    coder = {
+      source = "coder/coder"
+      version = "2.4.0-pre0"
+    }
+  }
+}
+
+data "coder_parameter" "word" {
+  name        = "word"
+  description = "Select something"
+  type        = "string"
+  order       = 1
+  # No default selected
+
+  option {
+    name  = "Bird"
+    value = "bird"
+    description = "An animal that can fly."
+  }
+  option {
+    name  = "Boat"
+    value = "boat"
+  }
+}

types/parameter.go

@@ -93,22 +93,35 @@ type ParameterOption struct {
 	Icon        string    `json:"icon"`
 }
 
-func (r *ParameterData) Valid() hcl.Diagnostics {
-	diag := (&provider.Parameter{
+func (r *ParameterData) Valid(value HCLString) hcl.Diagnostics {
+	var defPtr *string
+	if !r.DefaultValue.Value.IsNull() {
+		def := r.DefaultValue.Value.AsString()
+		defPtr = &def
+	}
+
+	var valuePtr *string
+	// TODO: What to do if it is not valid?
+	if value.Valid() {
+		val := value.Value.AsString()
+		valuePtr = &val
+	}
+
+	_, diag := (&provider.Parameter{
 		Name:        r.Name,
 		DisplayName: r.DisplayName,
 		Description: r.Description,
 		Type:        provider.OptionType(r.Type),
 		FormType:    r.FormType,
 		Mutable:     r.Mutable,
-		Default:     r.DefaultValue.AsString(),
+		Default:     defPtr,
 		Icon:        r.Icon,
 		Option:      providerOptions(r.Options),
 		Validation:  providerValidations(r.Validations),
 		Optional:    false,
 		Order:       int(r.Order),
 		Ephemeral:   r.Ephemeral,
-	}).Valid()
+	}).ValidateInput(valuePtr)
 
 	if diag.HasError() {
 		// TODO: We can take the attr path and decorate the error with

types/value.go

@@ -73,6 +73,14 @@ func StringLiteral(s string) HCLString {
 	}
 }
 
+func NullString() HCLString {
+	v := cty.NullVal(cty.String)
+	return HCLString{
+		Value:     v,
+		ValueExpr: &hclsyntax.LiteralValueExpr{Val: v},
+	}
+}
+
 // AsString is a safe function. It will always return a string.
 // The caller should check if this value is Valid and known before
 // calling this function.