Add errors to JSON output for files below minimum coverage

Report per-file minimum coverage violations in the JSON formatter,
supporting line, branch, and method coverage criteria. This makes the
JSON self-contained for downstream consumers (e.g. CI reporters) that
don't have access to the Ruby process to check exit codes.

Co-Authored-By: Tejas <tejas.shetty@mailbox.org>

Author: sferik

lib/simplecov/formatter/json_formatter/result_hash_formatter.rb

@@ -14,6 +14,7 @@ def format
           format_total
           format_files
           format_groups
+          format_errors
 
           formatted_result
         end
@@ -37,14 +38,31 @@ def format_groups
           end
         end
 
+        def format_errors
+          SimpleCov.minimum_coverage_by_file.each do |criterion, expected_percent|
+            @result.files.each do |file|
+              actual = SimpleCov.round_coverage(file.coverage_statistics.fetch(criterion).percent)
+              next unless actual < expected_percent
+
+              criterion_key = CRITERION_KEYS.fetch(criterion)
+              errors = formatted_result[:errors][criterion_key] ||= {}
+              errors[file.filename] = actual
+            end
+          end
+        end
+
+        CRITERION_KEYS = {line: :lines, branch: :branches, method: :methods}.freeze
+        private_constant :CRITERION_KEYS
+
         def formatted_result
           @formatted_result ||= {
             meta: {
               simplecov_version: SimpleCov::VERSION
             },
             total: {},
             coverage: {},
-            groups: {}
+            groups: {},
+            errors: {}
           }
         end
 

spec/fixtures/json/sample.json

@@ -43,5 +43,6 @@
       "lines_covered_percent": 90.0
     }
   },
-  "groups": {}
+  "groups": {},
+  "errors": {}
 }

spec/fixtures/json/sample_groups.json

@@ -53,5 +53,6 @@
         "strength": 0.0
       }
     }
-  }
+  },
+  "errors": {}
 }

spec/fixtures/json/sample_with_branch.json

@@ -65,5 +65,6 @@
       "branches_covered_percent": 50.0
     }
   },
-  "groups": {}
+  "groups": {},
+  "errors": {}
 }

spec/fixtures/json/sample_with_method.json

@@ -77,5 +77,6 @@
       "methods_covered_percent": 100.0
     }
   },
-  "groups": {}
+  "groups": {},
+  "errors": {}
 }

spec/json_formatter_spec.rb

@@ -107,6 +107,61 @@
       end
     end
 
+    context "with minimum_coverage_by_file for lines" do
+      before do
+        allow(SimpleCov).to receive(:minimum_coverage_by_file).and_return(line: 95)
+      end
+
+      it "reports files below the threshold in errors" do
+        subject.format(result)
+        errors = json_output.fetch("errors")
+        expect(errors).to eq(
+          "lines" => {source_fixture("json/sample.rb") => 90.0}
+        )
+      end
+    end
+
+    context "with minimum_coverage_by_file for branches" do
+      let(:result) do
+        SimpleCov::Result.new({
+                                source_fixture("json/sample.rb") => {
+                                  "lines" => [nil, 1, 1, 1, 1, nil, nil, 1, 1, nil, nil,
+                                              1, 1, 0, nil, 1, nil, nil, nil, nil, 1, 0, nil, nil, nil],
+                                  "branches" => {
+                                    [:if, 0, 13, 4, 17, 7] => {
+                                      [:then, 1, 14, 6, 14, 10] => 0,
+                                      [:else, 2, 16, 6, 16, 10] => 1
+                                    }
+                                  }
+                                }
+                              })
+      end
+
+      before do
+        enable_branch_coverage
+        allow(SimpleCov).to receive(:minimum_coverage_by_file).and_return(branch: 75)
+      end
+
+      it "reports files below the threshold in errors" do
+        subject.format(result)
+        errors = json_output.fetch("errors")
+        expect(errors).to eq(
+          "branches" => {source_fixture("json/sample.rb") => 50.0}
+        )
+      end
+    end
+
+    context "with minimum_coverage_by_file when all files pass" do
+      before do
+        allow(SimpleCov).to receive(:minimum_coverage_by_file).and_return(line: 80)
+      end
+
+      it "returns empty errors" do
+        subject.format(result)
+        expect(json_output.fetch("errors")).to eq({})
+      end
+    end
+
     context "with groups" do
       let(:line_stats) { SimpleCov::CoverageStatistics.new(covered: 8, missed: 2) }