Add descriptive message for unexpected DSL exceptions

Currently, when a DSL compiler raises an error while running a `decorate`
operation, it is not very obvious which compiler failed and during the
processing of which constant. The failing DSL compiler is kind of obvious
if one looks at the backtrace, but the constant that it is failing on
is very hard to understand if one is not running DSL generation in verbose
mode.

This PR handles unexpected exceptions, shows a friendly error message for
them and re-raises the exception to keep the current behaviour.

lib/tapioca/dsl/pipeline.rb

@@ -152,6 +152,9 @@ def rbi_for_constant(constant)
 
           compiler = compiler_class.new(self, file.root, constant)
           compiler.decorate
+        rescue
+          $stderr.puts("Error: `#{compiler_class.name}` failed to generate RBI for `#{constant}`")
+          raise # This is an unexpected error, so re-raise it
         end
 
         return if file.root.empty?

spec/tapioca/cli/dsl_spec.rb

@@ -1148,6 +1148,42 @@ class Image
           assert_project_file_exist("sorbet/rbi/dsl/job.rbi")
           assert_project_file_exist("sorbet/rbi/dsl/image.rbi")
         end
+
+        it "shows a helpful error message when unexpected errors occur" do
+          @project.write("lib/post.rb", <<~RB)
+            class Post
+            end
+          RB
+
+          @project.write("lib/compilers/post_compiler_that_raises.rb", <<~RB)
+            require "post"
+
+            class PostCompilerThatRaises < Tapioca::Dsl::Compiler
+              def decorate
+                raise "Some unexpected error happened"
+              end
+
+              def self.gather_constants
+                [::Post]
+              end
+            end
+          RB
+
+          result = @project.tapioca("dsl")
+
+          assert_equal(<<~OUT, result.out)
+            Loading Rails application... Done
+            Loading DSL compiler classes... Done
+            Compiling DSL RBI files...
+
+          OUT
+
+          assert_includes(result.err, "Error: `PostCompilerThatRaises` failed to generate RBI for `Post`")
+          assert_includes(result.err, "Some unexpected error happened")
+
+          refute_project_file_exist("sorbet/rbi/dsl/post.rbi")
+          refute_success_status(result)
+        end
       end
 
       describe "verify" do