Fixed CLI crashing after gem install

Gemfile

@@ -11,12 +11,12 @@ gem "rubocop", "~> 1.21"
 gem "rubocop-performance"
 gem "rubocop-rake"
 gem "rubocop-rspec"
-gem "tty-table"
 
 # Optional dependencies — loaded lazily by the feature that needs them.
 group :optional do
   gem "sinatra"      # Dcc::Server REST API
   gem "tty-prompt"   # dcc issue (interactive builder)
+  gem "tty-table"    # dcc extract files (aligned table)
 end
 
 gem "puma", "~> 8.0"

lib/dcc/cli/cli.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "thor"
-require "tty-table"
 
 # `Dcc::Cli::Cli` is the Thor-based command-line interface. Each subcommand
 # (validate, convert, extract, signature, transform, inspect, diff, issue)

lib/dcc/cli/formatters.rb

@@ -1,12 +1,30 @@
 # frozen_string_literal: true
 
-require "tty-table"
-
 module Dcc
   module Cli
     # `Dcc::Cli::Formatters` picks the right text/JSON/YAML representation
     # of a result model and prints it.
     module Formatters
+      # Goes to stderr, so a piped `extract files` still yields clean data.
+      TTY_TABLE_HINT = "note: install tty-table for aligned output " \
+                       "(gem install tty-table)"
+
+      # `tty-table` is optional. It pulls in eight further gems to prettify
+      # one command, which every library user would otherwise install just
+      # to parse XML. Loaded on first use, and its absence falls back to the
+      # plain renderer rather than raising the way `Dcc::Server` does.
+      def self.table_available?
+        return @table_available unless @table_available.nil?
+
+        begin
+          require "tty-table"
+          @table_available = true
+        rescue ::LoadError
+          @table_available = false
+        end
+        @table_available
+      end
+
       module_function
 
       def print(object, format: "text")
@@ -24,6 +42,14 @@ def print_files(files)
           return
         end
 
+        unless table_available?
+          # Hint first: a stderr that raises is caught by the rescue below,
+          # which re-runs the renderer. Printing first would duplicate it.
+          warn TTY_TABLE_HINT
+          print_files_plain(files)
+          return
+        end
+
         # TTY::Table calls ioctl which fails on StringIO / pipes. Fall back
         # to a plain-text rendering when stdout isn't a real terminal.
         if $stdout.is_a?(::IO) && !$stdout.tty?

spec/dcc/cli/dependencies_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+# The CLI ships as `exe/dcc`. Every gem it requires unconditionally must be a
+# declared runtime dependency, or `gem install dcc` yields a binary that
+# crashes on every command. A gem may be left undeclared only by naming it
+# in `optional`, which means its require is guarded and its absence degrades
+# the output instead of raising.
+# rubocop:disable RSpec/DescribeClass -- packaging invariant, not a class
+RSpec.describe "dcc CLI runtime dependencies" do
+  let(:root) { File.expand_path("../../..", __dir__) }
+  let(:gemspec) { Gem::Specification.load(File.join(root, "dcc.gemspec")) }
+  let(:declared) { gemspec.runtime_dependencies.map(&:name) }
+  # Matches indented requires (inside a method or conditional) and both quote
+  # styles. Does not match parenthesized, multiline, or interpolated requires
+  # -- add one of those and this guard will not see it.
+  let(:required) do
+    pattern = /^\s*require ["']([^"']+)["']/
+    Dir[File.join(root, "lib", "dcc", "cli", "**", "*.rb")]
+      .flat_map { |f| File.read(f).scan(pattern).flatten }
+      .reject { |name| name.start_with?("dcc/") }
+      .map { |name| name.split("/").first }
+      .uniq - stdlib
+  end
+
+  # Plain methods, not `let`, to stay under the memoized-helper limit.
+  def stdlib
+    %w[base64 bigdecimal csv date digest json open3 openssl set stringio yaml]
+  end
+
+  # `tty-table` costs eight further gems to prettify one command. Every
+  # library user would install them to parse XML. `formatters.rb` guards the
+  # require and falls back to its plain renderer instead.
+  def optional
+    %w[tty-table]
+  end
+
+  it "finds the gems the CLI requires" do
+    expect(required).to include("thor", "tty-table")
+  end
+
+  it "declares every third-party gem the CLI requires" do
+    expect(required - declared - optional).to be_empty
+  end
+
+  it "keeps the optional gems out of the gemspec" do
+    expect(declared).not_to include(*optional)
+  end
+end
+# rubocop:enable RSpec/DescribeClass

spec/dcc/cli/formatters_spec.rb

@@ -20,6 +20,44 @@
     end
   end
 
+  # The gem does not depend on tty-table, so this is what most installs see.
+  describe ".print_files without tty-table" do
+    let(:files) do
+      Dcc::V3.load_all!
+      Dcc::Extract::File.each(
+        Dcc.parse(File.read(fixtures_path("dcclib", "valid.xml"))),
+      )
+    end
+
+    before do
+      allow(described_class).to receive(:table_available?).and_return(false)
+    end
+
+    it "still renders every file" do
+      expect { described_class.print_files(files) }
+        .to output(/test\.txt/).to_stdout
+    end
+
+    it "points at the nicer output on stderr, not stdout" do
+      expect { described_class.print_files(files) }
+        .to output(/gem install tty-table/).to_stderr
+    end
+
+    it "keeps stdout free of the hint so piped output stays data" do
+      expect { described_class.print_files(files) }
+        .not_to output(/gem install/).to_stdout
+    end
+
+    # A stderr that raises lands in the method's `rescue StandardError`,
+    # which renders again. Anything parsing stdout would read the rows twice.
+    it "renders each file once when the hint cannot be written" do
+      allow(described_class).to receive(:warn).and_raise(Errno::EPIPE)
+
+      expect { described_class.print_files(files) }
+        .to output(satisfy { |out| out.scan("test.txt").size == 1 }).to_stdout
+    end
+  end
+
   describe ".print" do
     it "uses to_s by default" do
       result = Dcc::Validate::Result.new(issues: [], source: "xsd")