More flux->instFlux backwards compatibility in slot setup.

src/table/slots.cc

@@ -35,18 +35,42 @@ void FluxSlotDefinition::setKeys(std::string const &alias, Schema const &schema)
     _measKey = MeasKey();
     _errKey = ErrKey();
     _flagKey = Key<Flag>();
-    MeasFieldNameGetter helper(s["instFlux"], schema);
-    if (!helper.defined) {
-        return;
-    }
-    _measKey = helper.replaced;
+
+    // Helper function to set _measKey and _errKey.
+    // Returns false if this slot isn't defined.
+    auto setMeasAndErr = [&](std::string const & suffix) -> bool {
+        MeasFieldNameGetter helper(s[suffix], schema);
+        if (!helper.defined) {
+            return false;
+        }
+        _measKey = helper.replaced;
+        try {
+            _errKey = s[suffix + "Err"];
+        } catch (pex::exceptions::NotFoundError &) {
+            // not having an err key is not an error
+        }
+        return true;
+    };
+
     try {
-        _errKey = s["instFluxErr"];
-    } catch (pex::exceptions::NotFoundError &) {
+        if (!setMeasAndErr("instFlux")) {
+            return;
+        }
+    } catch (pex::exceptions::NotFoundError & err) {
+        // Alias was defined, but the field it targets doesn't exist.
+        // Before we assume the caller made a mistake and propagate the
+        // exception up, let's see if a field ending in "flux" rather
+        // than "instFlux" exists, for backwards compatibility.
+        try {
+            setMeasAndErr("flux");
+        } catch (pex::exceptions::NotFoundError &) {
+            throw err;  // rethrow the outer error for a better message
+        }
     }
     try {
         _flagKey = s["flag"];
     } catch (pex::exceptions::NotFoundError &) {
+        // not having a flag key is not an error
     }
 }