fix: builtin/terraform error while updating OpenTofu

opentofu/README.md

@@ -15,6 +15,11 @@ OpenTofu support for [`dependabot-core`][core-repo].
    [dependabot-core-dev] ~ $ cd opentofu && rspec
    ```
 
+3. Run against an existing repo:
+   ```
+   bin/dry-run.rb opentofu diofeher/dependabot-example --dep="specific-dependency"
+   ```
+
 ### Configuration
 
 To enable OpenTofu support, add to your `dependabot.yml`:

opentofu/lib/dependabot/opentofu/file_parser.rb

@@ -57,6 +57,7 @@ def ecosystem
       private
 
       # rubocop:disable Metrics/PerceivedComplexity
+      # rubocop:disable Metrics/MethodLength
       sig { params(dependency_set: Dependabot::FileParsers::Base::DependencySet).void }
       def parse_opentofu_files(dependency_set)
         opentofu_files.each do |file|
@@ -93,12 +94,20 @@ def parse_opentofu_files(dependency_set)
             required_providers = opentofu.fetch("required_providers", {})
             required_providers.each do |provider|
               provider.each do |name, details|
-                dependency_set << build_provider_dependency(file, name, details)
+                Dependabot.logger.info("Building provider dependency for #{name} in #{file.name}")
+                dep = build_provider_dependency(file, name, details)
+                if dep.name == "builtin/terraform"
+                  Dependabot.logger.info("Skipping builtin/terraform provider as it's not possible to update it")
+                  next
+                end
+
+                dependency_set << dep
               end
             end
           end
         end
       end
+      # rubocop:enable Metrics/MethodLength
 
       sig { params(dependency_set: Dependabot::FileParsers::Base::DependencySet).void }
       def parse_terragrunt_files(dependency_set)

opentofu/spec/dependabot/opentofu/file_parser_spec.rb

@@ -968,6 +968,29 @@
       end
     end
 
+    context "with a terraform.io/builtin/terraform provider" do
+      let(:files) { project_dependency_files("provider_with_builtin_terraform") }
+
+      it "skips the builtin/terraform provider" do
+        expect(dependencies.length).to eq(2)
+        # Should not include builtin/terraform provider
+        expect(dependencies.find { |d| d.name == "builtin/terraform" }).to be_nil
+        # Should include other providers
+        expect(dependencies.find { |d| d.name == "hashicorp/http" }).not_to be_nil
+        expect(dependencies.find { |d| d.name == "hashicorp/aws" }).not_to be_nil
+      end
+
+      it "parses other providers correctly" do
+        http_provider = dependencies.find { |d| d.name == "hashicorp/http" }
+        expect(http_provider.version).to eq("2.1.0")
+        expect(http_provider.requirements.first[:requirement]).to eq("~> 2.0")
+
+        aws_provider = dependencies.find { |d| d.name == "hashicorp/aws" }
+        expect(aws_provider.version).to eq("3.37.0")
+        expect(aws_provider.requirements.first[:requirement]).to eq("3.37.0")
+      end
+    end
+
     context "with a private module with directory suffix" do
       let(:files) { project_dependency_files("private_module_with_dir_suffix") }
 

opentofu/spec/fixtures/projects/provider_with_builtin_terraform/main.tf

@@ -0,0 +1,24 @@
+terraform {
+  required_version = ">= 1.0"
+
+  required_providers {
+    terraform = {
+      source  = "terraform.io/builtin/terraform"
+    }
+
+    http = {
+      source  = "hashicorp/http"
+      version = "~> 2.0"
+    }
+
+    aws = {
+      source  = "hashicorp/aws"
+      version = "3.37.0"
+    }
+  }
+}
+
+provider "aws" {
+  region = "eu-west-1"
+}
+