QE: say that a unit cell is required, instead of silently refusing to launch

Reported live: "drawing a molecule doesn't do anything when it comes to
creating a periodic system" and "Launch doesn't do anything".

pw.x is a plane-wave code and cannot run on a non-periodic structure.
ai.qe already refused loudly, naming the Builder's "Periodic Builder"
panel -- but only at input-generation time, after the user had set up the
entire calculation. And until the previous commit that message was being
discarded by CalcEd anyway.

Now the requirement is declared per code:

    <RequiresPeriodic>true</RequiresPeriodic>

which needed no parser change at all -- JCode::getValue() is a generic
getElementsByTagName lookup -- and keeps the knowledge next to the code
it describes rather than hardcoded in CalcEd.

CalcEd holds such a calculation not-ready, and says why. That second part
is the point: every OTHER reason a calculation is not ready is visible in
the panel that owns it (no theory, an incomplete basis), but a missing
unit cell is not, because nothing in CalcEd mentions cells at all. It
belongs to the structure and is created in a different application. So
the buttons just stayed greyed with no explanation, which is exactly what
"Launch doesn't do anything" looked like from outside.

Deliberately declarative rather than a QE special case: any future
plane-wave or solid-state code gets the same behaviour by adding one line
to its .edml.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFMUNbw2UpRPmgsqviAowb

Author: andy

data/client/cap/QuantumESPRESSO.edml

@@ -111,6 +111,13 @@
      one-input/one-output), md, and phonons (ph.x is a separate
      executable). -->
 <Editor theorydialog="qetheory.py" runtypedialog="qeruntype.py">
+  <!-- Plane waves cannot run without a cell, so CalcEd holds the
+       calculation not-ready and says why, instead of letting the user
+       complete the whole setup and discover it when ai.qe refuses at
+       generation time. Read generically by JCode::getValue(), so no
+       parser change was needed. -->
+  <RequiresPeriodic>true</RequiresPeriodic>
+
   <Theory category="PW" name="PW" needsBasis="false">
     <runtype>Energy</runtype>
     <runtype>Geometry</runtype>

src/apps/calced/CalcEd.C

@@ -2030,10 +2030,51 @@ bool CalcEd::theoryNeedsBasis() const
   return ret;
 }
 
+/**
+ * True when this code cannot run without a unit cell and the structure
+ * does not have one.
+ *
+ * Declared per code as <RequiresPeriodic>true</RequiresPeriodic> in its
+ * .edml. JCode::getValue() is a generic getElementsByTagName lookup, so
+ * this needed no parser change -- and being declarative keeps the
+ * knowledge next to the code it describes rather than hardcoded here.
+ *
+ * Quantum ESPRESSO is the case that motivated it: pw.x is a plane-wave
+ * code and cannot run on a non-periodic structure at all. ai.qe already
+ * refused loudly, naming the Builder's "Periodic Builder" panel -- but
+ * only at input-generation time, which is after the user has set up the
+ * whole calculation. Reported live as "drawing a molecule doesn't do
+ * anything when it comes to creating a periodic system" and "Launch
+ * doesn't do anything".
+ */
+bool CalcEd::requiresMissingCell() const
+{
+  if (p_code == 0 || p_frag == 0) {
+    return false;
+  }
+
+  string flag;
+  if (!p_code->get_string("RequiresPeriodic", flag)) {
+    return false;
+  }
+  if (flag != "true" && flag != "TRUE" && flag != "yes" && flag != "1") {
+    return false;
+  }
+
+  return (p_frag->getLattice() == (LatticeDef*)0);
+}
+
+
 bool CalcEd::isReady() const
 {
   bool ret = false;
 
+  //  A plane-wave code with no cell can never produce a valid deck, so
+  //  it is not ready however complete the rest of the setup is.
+  if (requiresMissingCell()) {
+    return false;
+  }
+
   if (p_iCalc->getState() < ResourceDescriptor::STATE_SUBMITTED
           && isDetailsReady()) {
     if (!theoryNeedsBasis()) {
@@ -2361,6 +2402,24 @@ void CalcEd::enableLaunch()
     if (ready) {
       p_feedback->setRunState(ResourceDescriptor::STATE_READY);
     } else {
+      //  Say WHY, for the one not-ready reason the user cannot deduce
+      //  from the setup panels. Everything else that blocks readiness
+      //  (no theory, an incomplete basis) is visible in the dialog that
+      //  owns it; a missing unit cell is not, because nothing in CalcEd
+      //  mentions cells at all -- it belongs to the structure, and is
+      //  created in a different application.
+      //
+      //  Without this the Launch and Final Edit buttons simply stay
+      //  greyed with no explanation, which is what "Launch doesn't do
+      //  anything" looked like from the outside.
+      if (requiresMissingCell()) {
+        p_feedback->setMessage(
+            "This code requires a periodic unit cell, and this structure "
+            "has none.\n"
+            "Open the structure in the Builder, show the \"Periodic "
+            "Builder\" tool panel, and create a lattice.",
+            WxFeedback::ERROR);
+      }
       if (p_iCalc->getState() == ResourceDescriptor::STATE_READY) {
         p_feedback->setRunState(ResourceDescriptor::STATE_CREATED);
       } else {

src/apps/calced/CalcEd.H

@@ -174,6 +174,7 @@ class CalcEd: public CalcEdGUI,
     bool isDetailsReady() const;
     bool theoryNeedsBasis() const;
     bool isReady() const;
+    bool requiresMissingCell() const;
     bool isGbsValid();
 
     // refresh & enable/disable & show/hide indicated field sets