Mismatched tests on map values produce incorrect logic. (#2754)

* fixed multiple mismatched tests for value maps.
* more fixes to map value checks. linter and test fixes.
* fixed to idiomatic Go.
* seenArgs wasn't being updated although the logic used it, fixed.
* added some math tests.
* readded some list optimizations because len checks exist.
* Review by Manish
* removed failure on undefined vars to return empty list, and reverted test to previous state.
* fixed bug in getReversePredicates.

query/math.go

@@ -19,6 +19,7 @@ package query
 import (
 	"github.com/dgraph-io/dgraph/types"
 	"github.com/dgraph-io/dgraph/x"
+	"github.com/golang/glog"
 )
 
 type mathTree struct {
@@ -31,7 +32,7 @@ type mathTree struct {
 
 // processBinary handles the binary operands like
 // +, -, *, /, %, max, min, logbase
-func processBinary(mNode *mathTree) (err error) {
+func processBinary(mNode *mathTree) error {
 	destMap := make(map[uint64]types.Val)
 	aggName := mNode.Fn
 
@@ -54,7 +55,7 @@ func processBinary(mNode *mathTree) (err error) {
 			// Use the constant value that was supplied.
 			rVal = cr
 		}
-		err = ag.ApplyVal(lVal)
+		err := ag.ApplyVal(lVal)
 		if err != nil {
 			return err
 		}
@@ -69,13 +70,12 @@ func processBinary(mNode *mathTree) (err error) {
 		return nil
 	}
 
-	if mpl != nil || mpr != nil {
+	if len(mpl) != 0 || len(mpr) != 0 {
 		for k := range mpr {
 			if err := f(k); err != nil {
 				return err
 			}
 		}
-
 		for k := range mpl {
 			if _, ok := mpr[k]; ok {
 				continue
@@ -85,15 +85,15 @@ func processBinary(mNode *mathTree) (err error) {
 			}
 		}
 		mNode.Val = destMap
-		return
+		return nil
 	}
 
 	if cl.Value != nil && cr.Value != nil {
 		// Both maps are nil, so 2 constatns.
 		ag := aggregator{
 			name: aggName,
 		}
-		err = ag.ApplyVal(cl)
+		err := ag.ApplyVal(cl)
 		if err != nil {
 			return err
 		}
@@ -104,13 +104,12 @@ func processBinary(mNode *mathTree) (err error) {
 		mNode.Const, err = ag.Value()
 		return err
 	}
-	x.Fatalf("Empty maps and constant")
 	return nil
 }
 
 // processUnary handles the unary operands like
 // u-, log, exp, since, floor, ceil
-func processUnary(mNode *mathTree) (err error) {
+func processUnary(mNode *mathTree) error {
 	destMap := make(map[uint64]types.Val)
 	srcMap := mNode.Child[0].Val
 	aggName := mNode.Fn
@@ -120,7 +119,7 @@ func processUnary(mNode *mathTree) (err error) {
 	}
 	if ch.Const.Value != nil {
 		// Use the constant value that was supplied.
-		err = ag.ApplyVal(ch.Const)
+		err := ag.ApplyVal(ch.Const)
 		if err != nil {
 			return err
 		}
@@ -129,7 +128,7 @@ func processUnary(mNode *mathTree) (err error) {
 	}
 
 	for k, val := range srcMap {
-		err = ag.ApplyVal(val)
+		err := ag.ApplyVal(val)
 		if err != nil {
 			return err
 		}
@@ -146,7 +145,7 @@ func processUnary(mNode *mathTree) (err error) {
 // processBinaryBoolean handles the binary operands which
 // return a boolean value.
 // All the inequality operators (<, >, <=, >=, !=, ==)
-func processBinaryBoolean(mNode *mathTree) (err error) {
+func processBinaryBoolean(mNode *mathTree) error {
 	destMap := make(map[uint64]types.Val)
 	srcMap := mNode.Child[0].Val
 	aggName := mNode.Fn
@@ -173,11 +172,11 @@ func processBinaryBoolean(mNode *mathTree) (err error) {
 }
 
 // processTernary handles the ternary operand cond()
-func processTernary(mNode *mathTree) (err error) {
+func processTernary(mNode *mathTree) error {
 	destMap := make(map[uint64]types.Val)
 	aggName := mNode.Fn
 	condMap := mNode.Child[0].Val
-	if condMap == nil {
+	if len(condMap) == 0 {
 		return x.Errorf("Expected a value variable in %v but missing.", aggName)
 	}
 	varOne := mNode.Child[1].Val
@@ -211,13 +210,13 @@ func processTernary(mNode *mathTree) (err error) {
 	return nil
 }
 
-func evalMathTree(mNode *mathTree) (err error) {
+func evalMathTree(mNode *mathTree) error {
 	if mNode.Const.Value != nil {
 		return nil
 	}
 	if mNode.Var != "" {
-		if mNode.Val == nil {
-			return x.Errorf("Variable %v not yet populated or missing.", mNode.Var)
+		if len(mNode.Val) == 0 {
+			glog.V(2).Infof("Variable %v not yet populated or missing.", mNode.Var)
 		}
 		// This is a leaf node whose value is already populated. So return.
 		return nil