fix(provider/docker): Ensure auto-assigned container name starts with valid characters (#13678)

* Ensure container name starts with valid characters when name is auto-assigned

plugins/providers/docker/action/create.rb

@@ -91,9 +91,7 @@ module VagrantPlugins
         def create_params
           container_name = @provider_config.name
           if !container_name
-            container_name = "#{@env[:root_path].basename.to_s}_#{@machine.name}"
-            container_name.gsub!(/[^-a-z0-9_]/i, "")
-            container_name << "_#{Time.now.to_i}"
+            container_name = generate_container_name
           end
 
           image = @env[:create_image]
@@ -156,6 +154,15 @@ module VagrantPlugins
 
           result
         end
+
+        def generate_container_name
+          container_name = "#{@env[:root_path].basename.to_s}_#{@machine.name}"
+          # Remove leading -/_ and any non-alphanumeric, non-hyphen/underscore characters
+          container_name.gsub!(/\A[^a-zA-Z0-9]+|[^-a-z0-9_]/i, "")
+          container_name << "_#{Time.now.to_i}"
+          container_name
+        end
+
       end
     end
   end

test/unit/plugins/providers/docker/action/create_test.rb

@@ -55,4 +55,62 @@ describe VagrantPlugins::DockerProvider::Action::Create do
       expect(result).to eq(["8125:8125", "8125:8125/udp"])
     end
   end
+
+  describe "#generate_container_name" do
+    let(:env) {{root_path: root_path}}
+    let(:root_path) {Pathname.new("/path/to/root")}
+
+    before do
+      subject.instance_variable_set(:@env, env)
+      subject.instance_variable_set(:@machine, machine)
+    end
+
+    it "should not remove any characters" do
+      expect(subject.generate_container_name).to start_with("root")
+    end
+
+    context "when root path starts with underscores" do
+      let(:root_path) {Pathname.new("/path/to/__root")}
+      it "should remove underscores" do
+        expect(subject.generate_container_name).to start_with("root")
+      end
+    end
+
+    context "when root path starts with dashes" do
+      let(:root_path) {Pathname.new("/path/to/--root")}
+      it "should remove dashes" do
+        expect(subject.generate_container_name).to start_with("root")
+      end
+    end
+
+    context "when root path starts with combination of invalid starting characters" do
+      let(:root_path) {Pathname.new("/path/to/_.-_-root")}
+      it "should remove invalid starting characters" do
+        expect(subject.generate_container_name).to start_with("root")
+      end
+    end
+
+    context "when root path ends with underscores" do
+      let(:root_path) {Pathname.new("/path/to/root__")}
+      it "should not remove trailing underscroes" do
+        expect(subject.generate_container_name).to start_with("root_")
+      end
+    end
+
+    context "when root path ends with invalid characters" do
+      let(:root_path) {Pathname.new("/path/to/root_.")}
+      it "should remove invalid trailing characters" do
+        expect(subject.generate_container_name).to start_with("root_")
+      end
+    end
+
+    context "when root path contains invalid characters" do
+      let(:root_path) {Pathname.new("/path/to/root-.path_.")}
+      it "should only remove invalid characters" do
+        expect(subject.generate_container_name).to start_with("root-path_")
+      end
+    end
+
+  end
+
 end