fix: support array-based JSON syntax in WalkExpressions (#422)

Author: bendrucker

plugin/internal/plugin2host/client.go

@@ -2,6 +2,7 @@ package plugin2host
 
 import (
 	"context"
+	stdjson "encoding/json"
 	"errors"
 	"fmt"
 	"os"
@@ -205,6 +206,69 @@ func (w *nativeWalker) Exit(node hclsyntax.Node) hcl.Diagnostics {
 	return nil
 }
 
+// extractJSONKeys extracts attribute names from JSON bytes using encoding/json.
+// This works for both object-based JSON {"foo": ...} and array-based JSON [{"foo": ...}].
+func extractJSONKeys(bytes []byte) ([]string, error) {
+	// Try to unmarshal as an object first
+	var obj map[string]any
+	if err := stdjson.Unmarshal(bytes, &obj); err == nil {
+		keys := make([]string, 0, len(obj))
+		for k := range obj {
+			keys = append(keys, k)
+		}
+		return keys, nil
+	}
+
+	// Try as an array of objects
+	var arr []map[string]any
+	if err := stdjson.Unmarshal(bytes, &arr); err != nil {
+		return nil, err
+	}
+
+	// Collect all unique keys from all objects in the array
+	keysMap := make(map[string]bool)
+	for _, obj := range arr {
+		for k := range obj {
+			keysMap[k] = true
+		}
+	}
+
+	keys := make([]string, 0, len(keysMap))
+	for k := range keysMap {
+		keys = append(keys, k)
+	}
+	return keys, nil
+}
+
+// getJSONAttributes gets all attributes from a JSON body, supporting both object
+// and array-based syntax. For array-based JSON like [{"import": {...}}], it
+// extracts attribute names using encoding/json and builds a schema to extract them.
+func getJSONAttributes(body hcl.Body, bytes []byte) (hcl.Attributes, hcl.Diagnostics) {
+	// First, try JustAttributes (works for object-based JSON)
+	attrs, diags := body.JustAttributes()
+	if !diags.HasErrors() {
+		return attrs, nil
+	}
+
+	// Extract keys using encoding/json
+	keys, err := extractJSONKeys(bytes)
+	if err != nil {
+		return attrs, diags // Return original JustAttributes error
+	}
+
+	// Build a schema with all discovered keys
+	schema := &hcl.BodySchema{
+		Attributes: make([]hcl.AttributeSchema, len(keys)),
+	}
+	for i, key := range keys {
+		schema.Attributes[i] = hcl.AttributeSchema{Name: key}
+	}
+
+	// Use PartialContent to get proper *json.expression objects
+	content, _, partialDiags := body.PartialContent(schema)
+	return content.Attributes, partialDiags
+}
+
 // WalkExpressions traverses expressions in all files by the passed walker.
 // Note that it behaves differently in native HCL syntax and JSON syntax.
 //
@@ -236,7 +300,7 @@ func (c *GRPCClient) WalkExpressions(walker tflint.ExprWalker) hcl.Diagnostics {
 		}
 
 		// In JSON syntax, everything can be walked as an attribute.
-		attrs, jsonDiags := file.Body.JustAttributes()
+		attrs, jsonDiags := getJSONAttributes(file.Body, file.Bytes)
 		if jsonDiags.HasErrors() {
 			diags = diags.Extend(jsonDiags)
 			continue

plugin/internal/plugin2host/plugin2host_test.go

@@ -1208,6 +1208,31 @@ data "terraform_remote_state" "remote_state" {
 				{Start: hcl.Pos{Line: 8, Column: 17}, End: hcl.Pos{Line: 8, Column: 32}},
 			},
 		},
+		{
+			name: "array-based json",
+			files: map[string][]byte{
+				"main.tf.json": []byte(`[
+  {
+    "resource": {
+      "null_resource": {
+        "foo": {}
+      }
+    }
+  },
+  {
+    "variable": {
+      "example": {
+        "type": "string"
+      }
+    }
+  }
+]`),
+			},
+			walked: []hcl.Range{
+				{Start: hcl.Pos{Line: 3, Column: 17}, End: hcl.Pos{Line: 7, Column: 6}},
+				{Start: hcl.Pos{Line: 10, Column: 17}, End: hcl.Pos{Line: 14, Column: 6}},
+			},
+		},
 	}
 
 	for _, test := range tests {