Add WalkExpressions function

helper/runner.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/terraform-linters/tflint-plugin-sdk/hclext"
 	"github.com/terraform-linters/tflint-plugin-sdk/terraform/addrs"
 	"github.com/terraform-linters/tflint-plugin-sdk/tflint"
@@ -124,6 +125,51 @@ func (r *Runner) GetFiles() (map[string]*hcl.File, error) {
 	return r.files, nil
 }
 
+type nativeWalker struct {
+	walker tflint.ExprWalker
+}
+
+func (w *nativeWalker) Enter(node hclsyntax.Node) hcl.Diagnostics {
+	if expr, ok := node.(hcl.Expression); ok {
+		return w.walker.Enter(expr)
+	}
+	return nil
+}
+
+func (w *nativeWalker) Exit(node hclsyntax.Node) hcl.Diagnostics {
+	if expr, ok := node.(hcl.Expression); ok {
+		return w.walker.Exit(expr)
+	}
+	return nil
+}
+
+func (r *Runner) WalkExpressions(walker tflint.ExprWalker) hcl.Diagnostics {
+	diags := hcl.Diagnostics{}
+	for _, file := range r.files {
+		if body, ok := file.Body.(*hclsyntax.Body); ok {
+			walkDiags := hclsyntax.Walk(body, &nativeWalker{walker: walker})
+			diags = diags.Extend(walkDiags)
+			continue
+		}
+
+		// In JSON syntax, everything can be walked as an attribute.
+		attrs, jsonDiags := file.Body.JustAttributes()
+		if jsonDiags.HasErrors() {
+			diags = diags.Extend(jsonDiags)
+			continue
+		}
+
+		for _, attr := range attrs {
+			enterDiags := walker.Enter(attr.Expr)
+			diags = diags.Extend(enterDiags)
+			exitDiags := walker.Exit(attr.Expr)
+			diags = diags.Extend(exitDiags)
+		}
+	}
+
+	return diags
+}
+
 // DecodeRuleConfig extracts the rule's configuration into the given value
 func (r *Runner) DecodeRuleConfig(name string, ret interface{}) error {
 	schema := hclext.ImpliedBodySchema(ret)

plugin/plugin2host/client.go

@@ -165,6 +165,62 @@ func (c *GRPCClient) GetFiles() (map[string]*hcl.File, error) {
 	return files, nil
 }
 
+type nativeWalker struct {
+	walker tflint.ExprWalker
+}
+
+func (w *nativeWalker) Enter(node hclsyntax.Node) hcl.Diagnostics {
+	if expr, ok := node.(hcl.Expression); ok {
+		return w.walker.Enter(expr)
+	}
+	return nil
+}
+
+func (w *nativeWalker) Exit(node hclsyntax.Node) hcl.Diagnostics {
+	if expr, ok := node.(hcl.Expression); ok {
+		return w.walker.Exit(expr)
+	}
+	return nil
+}
+
+func (c *GRPCClient) WalkExpressions(walker tflint.ExprWalker) hcl.Diagnostics {
+	files, err := c.GetFiles()
+	if err != nil {
+		return hcl.Diagnostics{
+			{
+				Severity: hcl.DiagError,
+				Summary:  "failed to call GetFiles()",
+				Detail:   err.Error(),
+			},
+		}
+	}
+
+	diags := hcl.Diagnostics{}
+	for _, file := range files {
+		if body, ok := file.Body.(*hclsyntax.Body); ok {
+			walkDiags := hclsyntax.Walk(body, &nativeWalker{walker: walker})
+			diags = diags.Extend(walkDiags)
+			continue
+		}
+
+		// In JSON syntax, everything can be walked as an attribute.
+		attrs, jsonDiags := file.Body.JustAttributes()
+		if jsonDiags.HasErrors() {
+			diags = diags.Extend(jsonDiags)
+			continue
+		}
+
+		for _, attr := range attrs {
+			enterDiags := walker.Enter(attr.Expr)
+			diags = diags.Extend(enterDiags)
+			exitDiags := walker.Exit(attr.Expr)
+			diags = diags.Extend(exitDiags)
+		}
+	}
+
+	return diags
+}
+
 // DecodeRuleConfig guesses the schema of the rule config from the passed interface and sends the schema to GRPC server.
 // Content retrieved based on the schema is decoded into the passed interface.
 func (c *GRPCClient) DecodeRuleConfig(name string, ret interface{}) error {

tflint/interface.go

@@ -108,6 +108,8 @@ type Runner interface {
 	// This is low level API for accessing information such as comments and syntax.
 	GetFiles() (map[string]*hcl.File, error)
 
+	WalkExpressions(walker ExprWalker) hcl.Diagnostics
+
 	// DecodeRuleConfig fetches the rule's configuration and reflects the result in the 2nd argument.
 	// The argument is expected to be a pointer to a structure tagged with hclext:
 	//

tflint/walker.go

@@ -0,0 +1,20 @@
+package tflint
+
+import (
+	"github.com/hashicorp/hcl/v2"
+)
+
+type ExprWalker interface {
+	Enter(expr hcl.Expression) hcl.Diagnostics
+	Exit(expr hcl.Expression) hcl.Diagnostics
+}
+
+type ExprWalkFunc func(expr hcl.Expression) hcl.Diagnostics
+
+func (f ExprWalkFunc) Enter(expr hcl.Expression) hcl.Diagnostics {
+	return f(expr)
+}
+
+func (f ExprWalkFunc) Exit(expr hcl.Expression) hcl.Diagnostics {
+	return nil
+}