fix: own legend label bytes in LegendEntryLabel forwarder (macOS issue #9)

daslib/implot_boost_v2.das

@@ -80,8 +80,10 @@ let private LEGEND_LABEL_RETRY_FRAMES = 240   // bounded window to resolve a jus
 
 def private capture_legend(var state : PlotScopeState; title : string) {
     // Read the plot's legend into the snapshot AFTER EndPlot, by title — the rect / shown are
-    // written during EndPlot's legend render, so GetPlot(title) gives current-frame values. Labels
-    // come from ImPlot as a fresh string per call, so we cache them (rebuild only when the entry set
+    // written during EndPlot's legend render, so GetPlot(title) gives current-frame values.
+    // LegendEntryLabel returns a das-heap-owned copy (it allocateString's into our context — see
+    // the C++ forwarder, issue #9), so the cached label stays valid even after ImPlot resets its
+    // internal Legend.Labels buffer next frame. We cache labels (rebuild only when the entry set
     // changes) rather than re-allocating every frame. Rects / shown are cheap scalars, refreshed
     // every frame. (A relabel with no count change reads stale — exotic for a steady plot.)
     let n = LegendEntryCount(title)

src/dasIMPLOT.main.cpp

@@ -150,10 +150,17 @@ int LegendEntryCount(const char* title) {
     ImPlotPlot* plot = ImPlot::GetPlot(title);
     return plot ? plot->Items.GetLegendCount() : 0;
 }
-const char* LegendEntryLabel(const char* title, int index) {
+// allocateString (das heap), NOT the raw GetLegendLabel pointer: that points into ImPlot's
+// per-frame Legend.Labels buffer, which the next BeginPlot/SetupFinish resets and may realloc — a
+// raw return would dangle by the time the snapshot serializes a frame later (empty/garbage on
+// macOS, issue #9). Owning the bytes here keeps the das string valid; mirrors the rest of the
+// string-returning API (dasImgui's text_range_string / ImGTB_Slice).
+char* LegendEntryLabel(const char* title, int index, das::Context* context, das::LineInfoArg* at) {
     ImPlotPlot* plot = ImPlot::GetPlot(title);
-    if (!plot || index < 0 || index >= plot->Items.GetLegendCount()) return "";
-    return plot->Items.GetLegendLabel(index);
+    if (!plot || index < 0 || index >= plot->Items.GetLegendCount())
+        return context->allocateString(nullptr, 0, at);
+    const char* label = plot->Items.GetLegendLabel(index);
+    return context->allocateString(label, strlen(label), at);
 }
 bool LegendEntryShown(const char* title, int index) {
     ImPlotPlot* plot = ImPlot::GetPlot(title);
@@ -287,7 +294,7 @@ void Module_dasIMPLOT::initMain () {
     addExtern<DAS_BIND_FUN(das::LegendEntryCount)>(*this, lib, "LegendEntryCount",
         SideEffects::accessExternal, "das::LegendEntryCount")->args({"title"});
     addExtern<DAS_BIND_FUN(das::LegendEntryLabel)>(*this, lib, "LegendEntryLabel",
-        SideEffects::accessExternal, "das::LegendEntryLabel")->args({"title", "index"});
+        SideEffects::accessExternal, "das::LegendEntryLabel")->args({"title", "index", "context", "lineinfo"});
     addExtern<DAS_BIND_FUN(das::LegendEntryShown)>(*this, lib, "LegendEntryShown",
         SideEffects::accessExternal, "das::LegendEntryShown")->args({"title", "index"});
     addExtern<DAS_BIND_FUN(das::LegendEntryHovered)>(*this, lib, "LegendEntryHovered",

tests/integration/test_multi_axes.das

@@ -37,12 +37,9 @@ def test_multi_axes(t : T?) {
         t |> success(abs(plot_axis_limit(m, s, "y2_max") - 1050.0lf) < 1.0lf, "Y2 (pressure) max captured ~1050")
         // The Y2-routed series' legend label resolves (the first-frame label fix). Poll, don't
         // one-shot: ImPlot can resolve the label a few frames after the item first registers, so a
-        // read on the axis-convergence snapshot races it. Skipped on macOS — the Y2-routed label
-        // stays empty there (issue #9, to be debugged on an osx box); the rail's drag checks below
-        // still run on all platforms.
-        if (get_platform_name() != "darwin") {
-            t |> success(wait_for_series_shown(s, "pressure", true) != null, "pressure series present in legend (Y2 label captured)")
-        }
+        // read on the axis-convergence snapshot races it. Now runs on all platforms — issue #9 (the
+        // macOS empty/garbage label) is fixed in the LegendEntryLabel forwarder (returns an owned copy).
+        t |> success(wait_for_series_shown(s, "pressure", true) != null, "pressure series present in legend (Y2 label captured)")
 
         // Drag ONLY the Y2 gutter: pressure's range must move while temp (Y1) and X1 stay put — the
         // independent-axis pan the tutorial teaches, distinct from a whole-plot body pan (moves all).