feat: add ifthen expression support (#72)

In this implementation IFTHEN is being treated as a built-in function.

src/substrait/textplan/converter/PlanPrinterVisitor.cpp

@@ -442,10 +442,33 @@ std::any PlanPrinterVisitor::visitWindowFunction(
 
 std::any PlanPrinterVisitor::visitIfThen(
  const ::substrait::proto::Expression::IfThen& ifthen) {
- errorListener_->addError(
- "If then expressions are not yet supported: " +
- ifthen.ShortDebugString());
- return std::string("IFTHEN_NOT_YET_IMPLEMENTED");
+ std::stringstream text;
+ text << "IFTHEN(";
+ bool hasPreviousText = false;
+ for (const auto& clause : ifthen.ifs()) {
+ if (!clause.has_if_() || !clause.has_then()) {
+ errorListener_->addError(
+ "If then clauses require both an if and a then expression: " +
+ clause.ShortDebugString());
+ continue;
+ }
+ if (hasPreviousText) {
+ text << ", ";
+ }
+ text << ANY_CAST(std::string, visitExpression(clause.if_()));
+ text << ", ";
+ text << ANY_CAST(std::string, visitExpression(clause.then()));
+ hasPreviousText = true;
+ }
+ if (ifthen.has_else_()) {
+ if (hasPreviousText) {
+ text << ", ";
+ }
+ text << ANY_CAST(std::string, visitExpression(ifthen.else_()));
+ }
+
+ text << ")";
+ return text.str();
 }
 
 std::any PlanPrinterVisitor::visitSwitchExpression(

src/substrait/textplan/converter/tests/BinaryToTextPlanConversionTest.cpp

@@ -464,6 +464,38 @@ std::vector<TestCase> getTestCases() {
  filter functionref#4(field#2, 0.07_fp64);
  })"))),
  },
+ {
+ "ifthen expression missing then",
+ R"(relations: {
+ root: {
+ input: {
+ filter: {
+ condition: {
+ if_then: {
+ ifs: {
+ if: {
+ literal: {
+ nullable: false,
+ fp64: 0.07
+ }
+ }
+ }
+ else: {
+ literal: {
+ nullable: false,
+ fp64: 0.07
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+ })",
+ HasErrors(
+ {"If then clauses require both an if and a then expression: "
+ "if { literal { fp64: 0.07 } }"}),
+ },
  {
  "cast expression",
  R"(relations: {

src/substrait/textplan/parser/SubstraitPlanRelationVisitor.cpp

@@ -10,6 +10,7 @@
 
 #include "SubstraitPlanParser/SubstraitPlanParser.h"
 #include "SubstraitPlanTypeVisitor.h"
+#include "absl/strings/ascii.h"
 #include "absl/strings/numbers.h"
 #include "date/tz.h"
 #include "substrait/expression/DecimalLiteral.h"
@@ -731,10 +732,39 @@ std::any SubstraitPlanRelationVisitor::visitExpression(
  return defaultResult();
 }
 
+::substrait::proto::Expression
+SubstraitPlanRelationVisitor::visitExpressionIfThenUse(
+ SubstraitPlanParser::ExpressionFunctionUseContext* ctx) {
+ ::substrait::proto::Expression expr;
+ size_t currExprNum = 0;
+ size_t totalExprCount = ctx->expression().size();
+ while (currExprNum + 2 <= totalExprCount) {
+ // Peel off an if/then pair.
+ auto ifThen = expr.mutable_if_then()->add_ifs();
+ *ifThen->mutable_if_() = ANY_CAST(
+ ::substrait::proto::Expression,
+ visitExpression(ctx->expression(currExprNum)));
+ *ifThen->mutable_then() = ANY_CAST(
+ ::substrait::proto::Expression,
+ visitExpression(ctx->expression(currExprNum + 1)));
+ currExprNum += 2;
+ }
+ if (currExprNum + 1 <= totalExprCount) {
+ // Use the last expression as the else clause.
+ *expr.mutable_if_then()->mutable_else_() = ANY_CAST(
+ ::substrait::proto::Expression,
+ visitExpression(ctx->expression(currExprNum)));
+ }
+ return expr;
+}
+
 std::any SubstraitPlanRelationVisitor::visitExpressionFunctionUse(
  SubstraitPlanParser::ExpressionFunctionUseContext* ctx) {
  ::substrait::proto::Expression expr;
  std::string funcName = ctx->id()->getText();
+ if (absl::AsciiStrToLower(funcName) == "ifthen") {
+ return visitExpressionIfThenUse(ctx);
+ }
  uint32_t funcReference = 0;
  auto symbol = symbolTable_->lookupSymbolByName(funcName);
  if (symbol == nullptr || symbol->type != SymbolType::kFunction) {

src/substrait/textplan/parser/SubstraitPlanRelationVisitor.h

@@ -8,6 +8,7 @@
 #include "substrait/textplan/parser/SubstraitPlanTypeVisitor.h"
 
 namespace substrait::proto {
+class Expression;
 class Expression_Literal;
 class Expression_Literal_Map_KeyValue;
 class NamedStruct;
@@ -71,6 +72,10 @@ class SubstraitPlanRelationVisitor : public SubstraitPlanTypeVisitor {
  // visitExpression is a new method delegating to the methods below.
  std::any visitExpression(SubstraitPlanParser::ExpressionContext* ctx);
 
+ // visitExpressionIfThenUse handles the built-in IFTHEN function-like syntax.
+ ::substrait::proto::Expression visitExpressionIfThenUse(
+ SubstraitPlanParser::ExpressionFunctionUseContext* ctx);
+
  std::any visitExpressionFunctionUse(
  SubstraitPlanParser::ExpressionFunctionUseContext* ctx) override;
 

src/substrait/textplan/tests/RoundtripTest.cpp

@@ -69,6 +69,11 @@ TEST_P(RoundTripBinaryToTextFixture, RoundTrip) {
  std::string outputText =
  SymbolTablePrinter::outputToText(textResult.getSymbolTable());
 
+ ASSERT_THAT(textResult, AllOf(ParsesOk(), HasErrors({})))
+ << std::endl
+ << "Intermediate result:" << std::endl
+ << addLineNumbers(outputText) << std::endl;
+
  auto stream = loadTextString(outputText);
  auto result = parseStream(stream);
  ASSERT_NO_THROW(auto outputBinary = SymbolTablePrinter::outputToBinaryPlan(