Parse variable validation

kylecarbs · johnstcn · commit 6d06d90c630e · 2025-01-07T17:57:19.000Z
diff --git a/tfconfig/load_hcl.go b/tfconfig/load_hcl.go
@@ -185,6 +185,35 @@ func LoadModuleFromFile(file *hcl.File, mod *Module) hcl.Diagnostics {
 				v.Sensitive = sensitive
 			}
 
+			for _, block := range content.Blocks {
+				switch block.Type {
+
+				case "validation":
+					content, _, contentDiags := block.Body.PartialContent(variableValidationSchema)
+					diags = append(diags, contentDiags...)
+					var variableValidation VariableValidation
+
+					if attr, defined := content.Attributes["condition"]; defined {
+						variableValidation.Condition = attr.Expr
+					}
+
+					if attr, defined := content.Attributes["error_message"]; defined {
+						var errorMessage string
+						valDiags := gohcl.DecodeExpression(attr.Expr, nil, &errorMessage)
+						diags = append(diags, valDiags...)
+						variableValidation.ErrorMessage = errorMessage
+					}
+
+					v.Validations = append(v.Validations, variableValidation)
+
+				default:
+					// Should never happen because our cases above should be
+					// exhaustive for our schema.
+					panic(fmt.Errorf("unhandled block type %q", block.Type))
+
+				}
+			}
+
 		case "output":
 
 			content, _, contentDiags := block.Body.PartialContent(outputSchema)
diff --git a/tfconfig/schema.go b/tfconfig/schema.go
@@ -79,6 +79,23 @@ var variableSchema = &hcl.BodySchema{
 			Name: "sensitive",
 		},
 	},
+	Blocks: []hcl.BlockHeaderSchema{
+		{
+			Type:       "validation",
+			LabelNames: nil,
+		},
+	},
+}
+
+var variableValidationSchema = &hcl.BodySchema{
+	Attributes: []hcl.AttributeSchema{
+		{
+			Name: "condition",
+		},
+		{
+			Name: "error_message",
+		},
+	},
 }
 
 var outputSchema = &hcl.BodySchema{
diff --git a/tfconfig/testdata/variable-validation/variable-validation.out.json b/tfconfig/testdata/variable-validation/variable-validation.out.json
@@ -0,0 +1,49 @@
+{
+    "path": "testdata/variable-validation",
+    "required_providers": {
+      "null": {}
+    },
+    "variables": {
+      "A": {
+        "name": "A",
+        "default": "A default",
+        "required": false,
+        "pos": {
+          "filename": "testdata/variable-validation/variable-validation.tf",
+          "line": 1
+        }
+      },
+      "B": {
+        "name": "B",
+        "default": "B default",
+        "required": false,
+        "pos": {
+          "filename": "testdata/variable-validation/variable-validation.tf",
+          "line": 5
+        },
+        "validations": [
+            {
+                "error_message": "B error message"
+            }
+        ]
+      }
+    },
+    "outputs": {},
+    "managed_resources": {
+      "null_resource.A": {
+        "mode": "managed",
+        "type": "null_resource",
+        "name": "A",
+        "provider": {
+          "name": "null"
+        },
+        "pos": {
+          "filename": "testdata/variable-validation/variable-validation.tf",
+          "line": 13
+        }
+      }
+    },
+    "data_resources": {},
+    "module_calls": {}
+  }
+  
diff --git a/tfconfig/testdata/variable-validation/variable-validation.out.md b/tfconfig/testdata/variable-validation/variable-validation.out.md
@@ -0,0 +1,13 @@
+
+# Module `testdata/variable-validation`
+
+Provider Requirements:
+* **null:** (any version)
+
+## Input Variables
+* `A` (default `"A default"`)
+* `B` (default `"B default"`)
+
+## Managed Resources
+* `null_resource.A` from `null`
+
diff --git a/tfconfig/testdata/variable-validation/variable-validation.tf b/tfconfig/testdata/variable-validation/variable-validation.tf
@@ -0,0 +1,13 @@
+variable "A" {
+    default = "A default"
+}
+
+variable "B" {
+    default = "B default"
+    validation {
+      condition = true
+      error_message = "B error message"
+    }
+}
+
+resource "null_resource" "A" {}
diff --git a/tfconfig/variable.go b/tfconfig/variable.go
@@ -3,6 +3,8 @@
 
 package tfconfig
 
+import "github.com/hashicorp/hcl/v2"
+
 // Variable represents a single variable from a Terraform module.
 type Variable struct {
 	Name        string `json:"name"`
@@ -17,5 +19,26 @@ type Variable struct {
 	Required  bool        `json:"required"`
 	Sensitive bool        `json:"sensitive,omitempty"`
 
+	Validations []VariableValidation `json:"validations,omitempty"`
+
 	Pos SourcePos `json:"pos"`
 }
+
+// VariableValidation represents a configuration-defined validation rule
+// for a particular input variable, given as a "validation" block inside
+// a "variable" block.
+type VariableValidation struct {
+	// Condition is an expression that refers to the variable being tested
+	// and contains no other references. The expression must return true
+	// to indicate that the value is valid or false to indicate that it is
+	// invalid. If the expression produces an error, that's considered a bug
+	// in the module defining the validation rule, not an error in the caller.
+	Condition hcl.Expression `json:"-"`
+
+	// ErrorMessage is one or more full sentences, which would need to be in
+	// English for consistency with the rest of the error message output but
+	// can in practice be in any language as long as it ends with a period.
+	// The message should describe what is required for the condition to return
+	// true in a way that would make sense to a caller of the module.
+	ErrorMessage string `json:"error_message"`
+}
