Stage builder helpers for creating Let expression is too restrictive

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    • Type: Bug
    • Resolution: Duplicate
    • Priority: Major - P3
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    • Affects Version/s: None
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      The stage builder can create multiple local variables in the same variable frame, even if the SBE engine creates multiple single-variable frames when lowering the tree of instructions.

      For instance, 

       

      optimizer::ABT makeLet(sbe::FrameId frameId, optimizer::ABTVector bindExprs, optimizer::ABT expr) {
    for (size_t idx = bindExprs.size(); idx > 0;) {
        --idx;
        expr = optimizer::make<optimizer::Let>(
            getABTLocalVariableName(frameId, idx), std::move(bindExprs[idx]), std::move(expr));
    }
    return expr;
}

       

      but when the Let instruction is built around a variable name, it asserts if there is a non-0 index

       

      optimizer::ABT makeLet(const optimizer::ProjectionName& name,
                       optimizer::ABT bindExpr,
                       optimizer::ABT expr) {
    // Verify that 'name' was generated by calling 'getABTLocalVariableName(N, 0)' for some
    // frame ID 'N'.
    auto localVarInfo = getSbeLocalVariableInfo(name);
    tassert(7654322, "", localVarInfo.has_value() && localVarInfo->second == 0);
    return optimizer::make<optimizer::Let>(name, std::move(bindExpr), std::move(expr));
}

       

      Given that SERVER-88687 changed the generation of Compare expressions to use non-0 indexes, either the restriction is lifted, or 0-based variable indexes are restored

       

       
 SbExpr generateExpressionCompare(StageBuilderState& state,
                                  ExpressionCompare::CmpOp op,
                                  SbExpr lhs,
                                  SbExpr rhs) {
     SbExprBuilder b(state);

     auto frameId = state.frameIdGenerator->generate();
     auto lhsVar = SbLocalVar{frameId, 0};
     auto rhsVar = SbLocalVar{frameId, 1};

       

      The failure can be reproduced by adding this entry in jstests/libs/block_processing_test_cases.js

               {
             name: "GroupByWithComplexIdExpr",
             pipeline: [
                 {$match: {[timeFieldName]: {$lt: dateMidPoint}}},
                 {
                     $group: {
                         _id: {
                             $lt: [
                                 29336,
                                 {$mod: ["$b", 1.0]}
                             ]
                         },
                     }
                 }
             ],
             usesBlockProcessing: featureFlagsAllowBlockHashAgg
         },

       

            Assignee:
            Drew Paroski
            Reporter:
            Alberto Massari
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              Created:
              Updated:
              Resolved: