Only build the parser's per-line coverage array when lines are being …

…counted The parser grew and filled its array of starting line counts for every parse made while coverage was set up, including Coverage.start(methods: true), where CoverageData#prepareCoverage never looks at it, and oneshot_lines, where it starts from an empty list instead. The file is still registered with Coverage in every mode so that it appears in the result.
headius · Sep 30, 2026 · Sep 14, 2026 · Sep 14, 2026 · Sep 14, 2026 · Sep 14, 2026
commit 34ecb4a4222dd3bc67ff09c01297abe304c9bb4a
diff --git a/core/src/main/java/org/jruby/ext/coverage/CoverageData.java b/core/src/main/java/org/jruby/ext/coverage/CoverageData.java
@@ -211,7 +211,8 @@ public synchronized Map<String, FileCoverage> resetCoverage() {
      * when lines are being measured.
      *
      * @param filename the file just parsed
-     * @param startingLines the initial per-line counts computed by the parser (-1 for lines without code)
+     * @param startingLines the initial per-line counts computed by the parser (-1 for lines without code); only
+     *                      consulted when lines are being counted
      * @return the file's entry, or null when coverage is not set up or the file has no name
      */
     public synchronized FileCoverage prepareCoverage(String filename, int[] startingLines) {

diff --git a/core/src/main/java/org/jruby/parser/RubyParserBase.java b/core/src/main/java/org/jruby/parser/RubyParserBase.java
@@ -2416,13 +2416,24 @@ public boolean isCoverageEnabled() {
         return runtime.isCoverageEnabled() && !isEval() || runtime.getCoverageData().isEvalCovered();
     }
 
+    /**
+     * Does this parse need the per-line array of starting counts? Only when lines are being counted: methods mode
+     * has no use for it and oneshot_lines starts from an empty list (see CoverageData#prepareCoverage).
+     */
+    private boolean isLineCountingEnabled() {
+        if (!isCoverageEnabled()) return false;
+
+        CoverageData data = runtime.getCoverageData();
+        return data.isLinesEnabled() && !data.isOneshot();
+    }
+
     /**
      * Zero out coverable lines as they're encountered
      */
     public void coverLine(int i) {
         // We had an overflow so we cannot mark whatever line this is as covered.
         if (i < 0) return;
-        if (isCoverageEnabled()) {
+        if (isLineCountingEnabled()) {
             growCoverageLines(i);
             coverage[i] = 0;
         }
@@ -2452,7 +2463,8 @@ public void growCoverageLines(int i) {
     public CoverageData finishCoverage(String file, int lines) {
         if (!isCoverageEnabled()) return null;
 
-        growCoverageLines(lines);
+        // the file is registered with Coverage in every mode; the line array is only filled in when lines are counted
+        if (isLineCountingEnabled()) growCoverageLines(lines);
         CoverageData data = runtime.getCoverageData();
         data.prepareCoverage(file, coverage);
         return data;