Give Coverage.line_stub an entry for every line of the file

The loop that padded the stub with nils compared against lines.size(), which grows as the loop appends, so it stopped about halfway to the end: a five-line method whose last statement is on line 2 got a four-entry stub. A last line with no newline was not counted at all. Pad until the stub has one entry per line, counting lines as File.foreach does, which is what CRuby's line_stub sizes its array by. SimpleCov builds the line coverage of files that were never loaded from line_stub, so those files were reported with lines missing. An empty file could still get a stub of [0]. Every parse shares the NilImplicitNode.NIL singleton, and an if with an empty else as the last statement of a block marked it as a newline through fixpos, so from then on the implicit nil at the root of an empty file counted as a line. Make NIL ignore setNewline and setLine so no parse can change it for later ones.
headius · Oct 2, 2026 · Sep 14, 2026 · Sep 16, 2026 · Sep 16, 2026 · Sep 16, 2026
commit 281bcb23b6d98fab8d295d28a749a5ce94e40a1e
diff --git a/core/src/main/java/org/jruby/ast/NilImplicitNode.java b/core/src/main/java/org/jruby/ast/NilImplicitNode.java
@@ -20,4 +20,13 @@ public NilImplicitNode() {
     public boolean isNil() {
         return true;
     }
+
+    // NIL is shared by every parse, so marking it for one AST would mark it in all later ones.
+    @Override
+    public void setNewline() {
+    }
+
+    @Override
+    public void setLine(int line) {
+    }
 }
diff --git a/core/src/main/java/org/jruby/parser/Parser.java b/core/src/main/java/org/jruby/parser/Parser.java
@@ -243,7 +243,7 @@ public IRubyObject getLineStub(ThreadContext context, ParseResult result, int li
         LineStubVisitor lineVisitor = new LineStubVisitor(context.runtime, lines);
         lineVisitor.visitRootNode(((RootNode) result));
 
-        for (int i = 0; i <= lineCount - lines.size(); i++) {
+        while (lines.size() < lineCount) {
             lines.append(context, context.nil);
         }
         return lines;

diff --git a/core/src/main/java/org/jruby/parser/ParserManager.java b/core/src/main/java/org/jruby/parser/ParserManager.java
@@ -172,10 +172,13 @@ public IRubyObject getLineStub(ThreadContext context, IRubyObject arg) {
         int length = contents.realSize();
         byte[] bytes = contents.unsafeBytes();
 
+        // One entry per line, as File.foreach yields them: a last line without a newline still counts.
+        int end = begin + length;
         int lineCount = 0;
-        for (int i = begin; i < length; i++) {
+        for (int i = begin; i < end; i++) {
             if (bytes[i] == '\n') lineCount++;
         }
+        if (length > 0 && bytes[end - 1] != '\n') lineCount++;
 
         // FIXME: Semantic problem.  Linenumber affects both differently due to prism being 1-indexed and AST being 0-indexed.
         ParseResult result = parseFile("", Options.PARSER_PRISM.load() ? 0 : -1, new LoadServiceResourceInputStream(contents.bytes()), contents.getEncoding());

diff --git a/test/jruby/test_coverage.rb b/test/jruby/test_coverage.rb
@@ -672,6 +672,33 @@ def test_ternary_arms_are_line_events
     RUBY
   end
 
+  def test_line_stub_has_an_entry_for_every_line
+    source = <<~'RUBY'
+      def show
+        @product = base_scope
+                   .includes(colors_products: :color)
+                   .find(params[:id])
+      end
+    RUBY
+    with_source(source) { |path| assert_equal [0, 0, nil, nil, nil], Coverage.line_stub(path) }
+    with_source(source.chomp) { |path| assert_equal [0, 0, nil, nil, nil], Coverage.line_stub(path) }
+    with_source("x = 1\n\n\n\n") { |path| assert_equal [0, nil, nil, nil], Coverage.line_stub(path) }
+    with_source("") { |path| assert_equal [], Coverage.line_stub(path) }
+  end
+
+  def test_line_stub_of_an_empty_file_after_an_empty_else
+    source = <<~'RUBY'
+      x.each do
+        if x
+          1
+        else
+        end
+      end
+    RUBY
+    with_source(source) { |path| Coverage.line_stub(path) }
+    with_source("") { |path| assert_equal [], Coverage.line_stub(path) }
+  end
+
   private
 
   def with_source(source)