Improved some error messages.

- DaphneDSLVisitor: made an error message start in lower case for consistency.
- Frame: error message in Frame::getColumnIdx() reports the available labels if the given one was not found (only up to five labels to avoid excessive output).
- setColLabels-kernel: reports also the numbers of found and given columns, in case of a mismatch.
- These improvements make debugging DaphneDSL scripts easier.

Author: pdamme

src/parser/daphnedsl/DaphneDSLVisitor.cpp

@@ -736,7 +736,7 @@ antlrcpp::Any DaphneDSLVisitor::visitArgExpr(DaphneDSLGrammarParser::ArgExprCont
         }
     } catch (std::exception &e) {
         throw ErrorHandler::compilerError(utils.getLoc(ctx->start), "DSLVisitor",
-                                          "Invalid literal value for argument '" + arg + "': " + argValue);
+                                          "invalid literal value for argument '" + arg + "': " + argValue);
     }
 
     mlir::Value lit = visitLiteral(literalCtx);

src/runtime/local/datastructures/Frame.h

@@ -336,7 +336,22 @@ class Frame : public Structure {
         auto it = labels2idxs.find(label);
         if (it != labels2idxs.end())
             return it->second;
-        throw std::runtime_error("column label not found: '" + label + "'");
+        std::stringstream msg;
+        msg << "column label not found: '" + label + "', available labels: ";
+        if (numCols == 0)
+            msg << "(none) (zero columns)";
+        else {
+            const size_t numLabelsPrintMax = 5;
+            const size_t numLabelsPrint = std::min(numCols, numLabelsPrintMax);
+            for (size_t i = 0; i < numLabelsPrint; i++) {
+                msg << '\'' << labels[i] << '\'';
+                if (i < numLabelsPrint - 1)
+                    msg << ", ";
+            }
+            if (numCols > numLabelsPrintMax)
+                msg << " (plus " << (numCols - numLabelsPrintMax) << " more)";
+        }
+        throw std::runtime_error(msg.str());
     }
 
     ValueTypeCode getColumnType(size_t idx) const {

src/runtime/local/kernels/SetColLabels.h

@@ -33,8 +33,9 @@
 inline void setColLabels(Frame *&res, const Frame *arg, const char **labels, size_t numLabels, DCTX(ctx)) {
     const size_t numCols = arg->getNumCols();
     if (numLabels != numCols)
-        throw std::runtime_error("the number of given labels does not match "
-                                 "the number of columns of the given frame");
+        throw std::runtime_error("the number of given labels (" + std::to_string(numLabels) +
+                                 ") does not match the number of columns of the given frame (" +
+                                 std::to_string(numCols) + ")");
     std::string *labelsStr = new std::string[numCols];
     for (size_t c = 0; c < numCols; c++)
         labelsStr[c] = labels[c];