Fix crashes with uneven number of nocov instructions

Fixes #846
We just assume them to go until the end. Test against a full nocov
for the file as well as a small mixture.

lib/simplecov/source_file.rb

@@ -164,9 +164,10 @@ def no_cov_chunks
     def build_no_cov_chunks
       no_cov_lines = src.map.with_index(1).select { |line, _index| LinesClassifier.no_cov_line?(line) }
 
-      warn "uneven number of nocov comments detected" if no_cov_lines.size.odd?
-
       no_cov_lines.each_slice(2).map do |(_line_start, index_start), (_line_end, index_end)|
+        # if we have an uneven number of nocovs we assume they go to the
+        # end of the file
+        index_end ||= src.size
         index_start..index_end
       end
     end

spec/fixtures/coverer.rb

@@ -2,6 +2,8 @@
 
 require "coverage"
 Coverage.start(:all)
-require_relative "branch_tester_script"
+require_relative "uneven_nocovs"
+
+UnevenNocov.call(42)
 
 p Coverage.result

spec/fixtures/single_nocov.rb

@@ -0,0 +1,14 @@
+# :nocov:
+module SingleNocov
+  def self.call(arg)
+    if arg.odd?
+      :odd
+    elsif arg == 30
+      :mop
+    elsif arg == 42
+      :yay
+    else
+      :nay
+    end
+  end
+end

spec/fixtures/uneven_nocovs.rb

@@ -0,0 +1,16 @@
+module UnevenNocov
+  def self.call(arg)
+    # :nocov:
+    if arg.odd?
+      :odd
+    elsif arg == 30
+      :mop
+    # :nocov:
+    elsif arg == 42
+      :yay
+    # :nocov:
+    else
+      :nay
+    end
+  end
+end

spec/source_file_spec.rb

@@ -606,4 +606,93 @@
       end
     end
   end
+
+  context "a file entirely ignored with a single # :nocov:" do
+    COVERAGE_FOR_SINGLE_NOCOV_RB = {
+      "lines" => [nil, 1, 1, 1, 0, 1, 0, 1, 1, nil, 0, nil, nil, nil],
+      "branches" => {
+        [:if, 0, 8, 4, 11, 10] =>
+          {[:then, 1, 9, 6, 9, 10] => 1, [:else, 2, 11, 6, 11, 10] => 0},
+        [:if, 3, 6, 4, 11, 10] =>
+          {[:then, 4, 7, 6, 7, 10] => 0, [:else, 5, 8, 4, 11, 10] => 1},
+        [:if, 6, 4, 4, 12, 7] =>
+          {[:then, 7, 5, 6, 5, 10] => 0, [:else, 8, 6, 4, 11, 10] => 1}
+      }
+    }.freeze
+
+    subject do
+      SimpleCov::SourceFile.new(source_fixture("single_nocov.rb"), COVERAGE_FOR_SINGLE_NOCOV_RB)
+    end
+
+    describe "line coverage" do
+      it "has all lines skipped" do
+        expect(subject.skipped_lines.size).to eq(subject.lines.size)
+        expect(subject.skipped_lines.size).to eq(14)
+      end
+
+      it "reports 100% coverage on 0/0" do
+        expect(subject.covered_percent).to eq 100.0
+        expect(subject.relevant_lines).to eq 0
+        expect(subject.covered_lines.size).to eq 0
+      end
+    end
+
+    describe "branch coverage" do
+      it "has 100% branch coverage on 0/0" do
+        branch_coverage = subject.coverage_statistics.fetch(:branch)
+
+        expect(branch_coverage.percent).to eq 100.0
+        expect(branch_coverage.total).to eq 0
+        expect(branch_coverage.covered).to eq 0
+      end
+
+      it "has all branches marked as skipped" do
+        expect(subject.branches.all?(&:skipped?)).to eq true
+      end
+    end
+  end
+
+  context "a file with an uneven usage of # :nocov:s" do
+    COVERAGE_FOR_UNEVEN_NOCOV_RB = {
+      "lines" => [1, 1, nil, 1, 0, 1, 0, nil, 1, 1, nil, nil, 0, nil, nil, nil],
+      "branches" => {
+        [:if, 0, 9, 4, 13, 10] =>
+          {[:then, 1, 10, 6, 10, 10] => 1, [:else, 2, 13, 6, 13, 10] => 0},
+        [:if, 3, 6, 4, 13, 10] =>
+          {[:then, 4, 7, 6, 7, 10] => 0, [:else, 5, 9, 4, 13, 10] => 1},
+        [:if, 6, 4, 4, 14, 7] =>
+          {[:then, 7, 5, 6, 5, 10] => 0, [:else, 8, 6, 4, 13, 10] => 1}
+      }
+    }.freeze
+
+    subject do
+      SimpleCov::SourceFile.new(source_fixture("uneven_nocovs.rb"), COVERAGE_FOR_UNEVEN_NOCOV_RB)
+    end
+
+    describe "line coverage" do
+      it "has 12 lines skipped" do
+        expect(subject.skipped_lines.size).to eq(12)
+      end
+
+      it "reports 100% coverage on 4/4" do
+        expect(subject.covered_percent).to eq 100.0
+        expect(subject.relevant_lines).to eq 4
+        expect(subject.covered_lines.size).to eq 4
+      end
+    end
+
+    describe "branch coverage" do
+      it "has 100% branch coverage on 1/1" do
+        branch_coverage = subject.coverage_statistics.fetch(:branch)
+
+        expect(branch_coverage.percent).to eq 100.0
+        expect(branch_coverage.total).to eq 1
+        expect(branch_coverage.covered).to eq 1
+      end
+
+      it "has 5 branches marked as skipped" do
+        expect(subject.branches.select(&:skipped?).size).to eq 5
+      end
+    end
+  end
 end