feat: add support to conditional code generation on genhcl/genfile (#371

)

docs/codegen/generate-file.md

@@ -72,7 +72,7 @@ Conditional code generation is achieved by the use of the `condition` attribute.
 The `condition` attribute should always evaluate to a boolean. The file will
 be generated only if it evaluates to **true**.
 
-If the `condition` attribute is absent then it is assumed to be always true.
+If the `condition` attribute is absent then it is assumed to be true.
 
 Any expression that produces a boolean can be used, including references
 to globals and function calls. For example:
@@ -87,3 +87,5 @@ generate_file "file" {
 
 Will only generate the file for stacks that the expression
 `tm_length(global.list) > 0` evaluates to true.
+
+When `condition` is false the `content` attribute won't be evaluated.

docs/codegen/generate-hcl.md

@@ -131,7 +131,7 @@ Conditional code generation is achieved by the use of the `condition` attribute.
 The `condition` attribute should always evaluate to a boolean. The file will
 be generated only if it evaluates to **true**.
 
-If the `condition` attribute is absent then it is assumed to be always true.
+If the `condition` attribute is absent then it is assumed to be true.
 
 Any expression that produces a boolean can be used, including references
 to globals and function calls. For example:
@@ -150,6 +150,8 @@ generate_hcl "file" {
 Will only generate the file for stacks that the expression
 `tm_length(global.list) > 0` evaluates to true.
 
+When `condition` is false the `content` block won't be evaluated.
+
 
 ## Partial Evaluation
 

generate/genfile/genfile.go

@@ -27,13 +27,20 @@ import (
 )
 
 const (
-	// ErrInvalidContentType indicates the content attribute on
-	// generate_file has a invalid type.
+	// ErrInvalidContentType indicates the content attribute
+	// has an invalid type.
 	ErrInvalidContentType errors.Kind = "invalid content type"
 
+	// ErrInvalidConditionType indicates the condition attribute
+	// has an invalid type.
+	ErrInvalidConditionType errors.Kind = "invalid condition type"
+
 	// ErrContentEval indicates an error when evaluating the content attribute.
 	ErrContentEval errors.Kind = "evaluating content"
 
+	// ErrConditionEval indicates an error when evaluating the condition attribute.
+	ErrConditionEval errors.Kind = "evaluating condition"
+
 	// ErrLabelConflict indicates the two generate_file blocks
 	// have the same label.
 	ErrLabelConflict errors.Kind = "label conflict detected"
@@ -47,8 +54,9 @@ type StackFiles struct {
 
 // File represents generated file from a single generate_file block.
 type File struct {
-	origin string
-	body   string
+	origin    string
+	body      string
+	condition bool
 }
 
 // Body returns the file body.
@@ -62,6 +70,12 @@ func (f File) Origin() string {
 	return f.origin
 }
 
+// Condition returns the result of the evaluation of the
+// condition attribute for the generated code.
+func (f File) Condition() bool {
+	return f.condition
+}
+
 // Header returns the header of this file.
 func (f File) Header() string {
 	// For now we don't support headers for arbitrary files
@@ -120,6 +134,34 @@ func Load(rootdir string, sm stack.Metadata, globals stack.Globals) (StackFiles,
 			Str("block", name).
 			Logger()
 
+		logger.Trace().Msg("evaluating condition")
+
+		condition := true
+		if genFileBlock.block.Condition != nil {
+			logger.Trace().Msg("has condition attribute, evaluating it")
+			value, err := evalctx.Eval(genFileBlock.block.Condition.Expr)
+			if err != nil {
+				return StackFiles{}, errors.E(ErrConditionEval, err)
+			}
+			if value.Type() != cty.Bool {
+				return StackFiles{}, errors.E(
+					ErrInvalidConditionType,
+					"condition has type %s but must be boolean",
+					value.Type().FriendlyName(),
+				)
+			}
+			condition = value.True()
+		}
+
+		if !condition {
+			logger.Trace().Msg("condition=false, content wont be evaluated")
+			res.files[name] = File{
+				origin:    genFileBlock.origin,
+				condition: condition,
+			}
+			continue
+		}
+
 		logger.Trace().Msg("evaluating contents")
 
 		value, err := evalctx.Eval(genFileBlock.block.Content.Expr)
@@ -136,8 +178,9 @@ func Load(rootdir string, sm stack.Metadata, globals stack.Globals) (StackFiles,
 		}
 
 		res.files[name] = File{
-			origin: genFileBlock.origin,
-			body:   value.AsString(),
+			origin:    genFileBlock.origin,
+			body:      value.AsString(),
+			condition: condition,
 		}
 	}