Display line diffs in dsl --verify error messages

README.md

@@ -502,6 +502,8 @@ Options:
   -w,        [--workers=N]                                                                         # Number of parallel workers to use when generating RBIs (default: auto)
              [--rbi-max-line-length=N]                                                             # Set the max line length of generated RBIs. Signatures longer than the max line length will be wrapped
                                                                                                    # Default: 120
+             [--max-diff-lines=N]                                                                  # Max number of diff lines to include in the `dsl --verify` output
+                                                                                                   # Default: 250
   -e,        [--environment=ENVIRONMENT]                                                           # The Rack/Rails environment to use when generating RBIs
                                                                                                    # Default: development
   -l,        [--list-compilers], [--no-list-compilers], [--skip-list-compilers]                    # List all loaded compilers
@@ -960,6 +962,7 @@ dsl:
   quiet: false
   workers: 1
   rbi_max_line_length: 120
+  max_diff_lines: 250
   environment: development
   list_compilers: false
   app_root: "."

lib/tapioca.rb

@@ -32,6 +32,7 @@ class Error < StandardError; end
 
   DEFAULT_RBI_MAX_LINE_LENGTH = 120
   DEFAULT_ENVIRONMENT = "development"
+  DEFAULT_MAX_DIFF_LINES = 250
 
   CENTRAL_REPO_ROOT_URI = "https://raw.githubusercontent.com/Shopify/rbi-central/main"
   CENTRAL_REPO_INDEX_PATH = "index.json"

lib/tapioca/cli.rb

@@ -116,6 +116,10 @@ def todo
       type: :numeric,
       desc: "Set the max line length of generated RBIs. Signatures longer than the max line length will be wrapped",
       default: DEFAULT_RBI_MAX_LINE_LENGTH
+    option :max_diff_lines,
+      type: :numeric,
+      desc: "Max number of diff lines to include in the `dsl --verify` output",
+      default: DEFAULT_MAX_DIFF_LINES
     option :environment,
       aliases: ["-e"],
       type: :string,
@@ -166,6 +170,7 @@ def dsl(*constant_or_paths)
         halt_upon_load_error: options[:halt_upon_load_error],
         compiler_options: options[:compiler_options],
         lsp_addon: self.class.addon_mode,
+        max_diff_lines: options[:max_diff_lines],
       }
 
       command = if options[:verify]

lib/tapioca/commands/abstract_dsl.rb

@@ -26,7 +26,8 @@ class AbstractDsl < CommandWithoutTracker
       #|   ?app_root: String,
       #|   ?halt_upon_load_error: bool,
       #|   ?compiler_options: Hash[String, untyped],
-      #|   ?lsp_addon: bool
+      #|   ?lsp_addon: bool,
+      #|   ?max_diff_lines: Integer
       #| ) -> void
       def initialize(
         requested_constants:,
@@ -46,7 +47,8 @@ def initialize(
         app_root: ".",
         halt_upon_load_error: true,
         compiler_options: {},
-        lsp_addon: false
+        lsp_addon: false,
+        max_diff_lines: DEFAULT_MAX_DIFF_LINES
       )
         @requested_constants = requested_constants
         @requested_paths = requested_paths
@@ -66,6 +68,7 @@ def initialize(
         @skip_constant = skip_constant
         @compiler_options = compiler_options
         @lsp_addon = lsp_addon
+        @max_diff_lines = max_diff_lines
 
         super()
       end
@@ -242,7 +245,7 @@ def compile_dsl_rbi(constant_name, rbi, outpath: @outpath, quiet: false)
       def perform_dsl_verification(dir)
         diff = verify_dsl_rbi(tmp_dir: dir)
 
-        report_diff_and_exit_if_out_of_date(diff, :dsl)
+        report_diff_and_exit_if_out_of_date(diff, tmp_dir: dir, command: :dsl)
       ensure
         FileUtils.remove_entry(dir)
       end
@@ -305,26 +308,67 @@ def build_error_for_files(cause, files)
         "  File(s) #{cause}:\n  - #{filenames}"
       end
 
-      #: (Hash[String, Symbol] diff, Symbol command) -> void
-      def report_diff_and_exit_if_out_of_date(diff, command)
+      #: (Hash[String, Symbol] diff, tmp_dir: Pathname, command: Symbol) -> void
+      def report_diff_and_exit_if_out_of_date(diff, tmp_dir:, command:)
         if diff.empty?
           say("Nothing to do, all RBIs are up-to-date.")
-        else
-          reasons = diff.group_by(&:last).sort.map do |cause, diff_for_cause|
-            build_error_for_files(cause, diff_for_cause.map(&:first))
-          end.join("\n")
+          return
+        end
+
+        reasons = diff.group_by(&:last).sort.map do |cause, diff_for_cause|
+          build_error_for_files(cause, diff_for_cause.map(&:first))
+        end.join("\n")
+
+        diff_output = build_diff_output(diff, tmp_dir)
+        diff_lines = diff_output.count("\n")
+
+        diff_section =
+          if diff_lines.between?(1, @max_diff_lines)
+            "#{set_color("Diff:", :red)}\n#{diff_output.chomp}"
+          elsif diff_lines > @max_diff_lines
+            truncated_output = diff_output.lines.first(@max_diff_lines).join
+            "#{set_color("Diff truncated to #{@max_diff_lines} lines:", :red)}\n#{truncated_output.rstrip}"
+          else
+            ""
+          end
+
+        raise Tapioca::Error, <<~ERROR.rstrip
+          #{set_color("RBI files are out-of-date. In your development environment, please run:", :green)}
+            #{set_color("`#{default_command(command)}`", :green, :bold)}
+          #{set_color("Once it is complete, be sure to commit and push any changes", :green)}
+          If you don't observe any changes after running the command locally, ensure your database is in a good
+          state e.g. run `bin/rails db:reset`
 
-          raise Tapioca::Error, <<~ERROR
-            #{set_color("RBI files are out-of-date. In your development environment, please run:", :green)}
-              #{set_color("`#{default_command(command)}`", :green, :bold)}
-            #{set_color("Once it is complete, be sure to commit and push any changes", :green)}
-            If you don't observe any changes after running the command locally, ensure your database is in a good
-            state e.g. run `bin/rails db:reset`
+          #{set_color("Reason:", :red)}
+          #{reasons}
 
-            #{set_color("Reason:", :red)}
-            #{reasons}
-          ERROR
+          #{diff_section}
+        ERROR
+      end
+
+      #: (Hash[String, Symbol] diff, Pathname tmp_dir) -> String
+      def build_diff_output(diff, tmp_dir)
+        out = String.new
+        line_count = 0
+
+        diff.each do |file, status|
+          filename = file.to_s
+          old_path = (@outpath / file).to_s
+          new_path = (tmp_dir / file).to_s
+
+          chunk = case status
+          when :added then file_diff(filename, File::NULL, new_path)
+          when :removed then file_diff(filename, old_path, File::NULL)
+          when :changed then file_diff(filename, old_path, new_path)
+          else ""
+          end
+
+          out << chunk
+          line_count += chunk.count("\n")
+          break if line_count > @max_diff_lines
         end
+
+        out
       end
 
       #: (Pathname path) -> Array[Pathname]

lib/tapioca/helpers/rbi_files_helper.rb

@@ -1,6 +1,8 @@
 # typed: strict
 # frozen_string_literal: true
 
+require "open3"
+
 module Tapioca
   # @requires_ancestor: Thor::Shell
   # @requires_ancestor: SorbetHelper
@@ -137,6 +139,30 @@ def validate_rbi_files(command:, gem_dir:, dsl_dir:, auto_strictness:, gems: [],
       Kernel.raise Tapioca::Error, error_messages.join("\n") if parse_errors.any?
     end
 
+    #: (String filename, String old_path, String new_path) -> String
+    def file_diff(filename, old_path, new_path)
+      stdout, stderr, status = Open3.capture3(
+        "diff",
+        "-u",
+        "--label",
+        filename,
+        "--label",
+        filename,
+        old_path,
+        new_path,
+      )
+
+      unless [0, 1].include?(status.exitstatus)
+        say_error("Failed to create #{filename} diff. #{stderr.chomp}", :red)
+        return ""
+      end
+
+      stdout
+    rescue => e
+      say_error("Failed to create #{filename} diff. #{e.message}", :red)
+      ""
+    end
+
     private
 
     #: (RBI::Index index, Array[String] files, number_of_workers: Integer?) -> void