[SYSTEMDS-1151] Fix error handling left indexing w/ scalars

This patch creates consistency of error messages for left indexing
(e.g., A[a:b,c:d] = x) for matrix and scalar right-hand-sides.

src/main/java/org/apache/sysds/runtime/matrix/data/MatrixBlock.java

@@ -4166,19 +4166,10 @@ public final MatrixBlock leftIndexingOperations(MatrixBlock rhsMatrix,
 	}
 
 	public MatrixBlock leftIndexingOperations(MatrixBlock rhsMatrix,
-			int rl, int ru, int cl, int cu, MatrixBlock ret, UpdateType update) {
+			int rl, int ru, int cl, int cu, MatrixBlock ret, UpdateType update)
+	{
 		// Check the validity of bounds
-		if( rl < 0 || rl >= getNumRows() || ru < rl || ru >= getNumRows()
-			|| cl < 0 || cl >= getNumColumns() || cu < cl || cu >= getNumColumns() ) {
-			throw new DMLRuntimeException("Invalid values for matrix indexing: ["+(rl+1)+":"+(ru+1)+"," 
-				+ (cl+1)+":"+(cu+1)+"] " + "must be within matrix dimensions ["+getNumRows()+","+getNumColumns()+"].");
-		}
-		if( (ru-rl+1) != rhsMatrix.getNumRows() || (cu-cl+1) != rhsMatrix.getNumColumns() ) {
-			throw new DMLRuntimeException("Invalid values for matrix indexing: " +
-				"dimensions of the source matrix ["+rhsMatrix.getNumRows()+"x" + rhsMatrix.getNumColumns() + "] " +
-				"do not match the shape of the matrix specified by indices [" +
-				(rl+1) +":" + (ru+1) + ", " + (cl+1) + ":" + (cu+1) + "] (i.e., ["+(ru-rl+1)+"x"+(cu-cl+1)+"]).");
-		}
+		checkDimsForLeftIndexing(rl, ru, cl, cu, true, rhsMatrix.rlen, rhsMatrix.clen);
 
 		MatrixBlock result = ret;
 		boolean sp = estimateSparsityOnLeftIndexing(rlen, clen, nonZeros,
@@ -4260,9 +4251,12 @@ else if( !result.sparse && sp )
 	 * @param update ?
 	 * @return matrix block
 	 */
-	public MatrixBlock leftIndexingOperations(ScalarObject scalar, int rl, int cl, MatrixBlock ret, UpdateType update) {
+	public MatrixBlock leftIndexingOperations(ScalarObject scalar, int rl, int cl,
+		MatrixBlock ret, UpdateType update)
+	{
 		double inVal = scalar.getDoubleValue();
 		boolean sp = estimateSparsityOnLeftIndexing(rlen, clen, nonZeros, 1, 1, (inVal!=0)?1:0);
+		checkDimsForLeftIndexing(rl, rl, cl, cl, false, -1, -1);
 
 		if( !update.isInPlace() ) { //general case
 			if(ret==null)
@@ -4283,7 +4277,28 @@ public MatrixBlock leftIndexingOperations(ScalarObject scalar, int rl, int cl, M
 		ret.quickSetValue(rl, cl, inVal);
 		return ret;
 	}
-
+
+	private void checkDimsForLeftIndexing(int rl, int ru, int cl, int cu,
+		boolean checkSrc, int rhsr, int rhsc)
+	{
+		int rlen = getNumRows(), clen = getNumColumns();
+		if( rl < 0 || rl >= rlen || ru < rl || ru >= rlen
+			|| cl < 0 || cl >= clen || cu < cl || cu >= clen ) {
+			throw new DMLRuntimeException("Invalid values for matrix indexing: "
+				+ "["+(rl+1)+":"+(ru+1)+"," + (cl+1)+":"+(cu+1)+"] " 
+				+ "must be within matrix dimensions ["+rlen+"x"+clen+"].");
+		}
+		if( checkSrc ) {
+			if( (ru-rl+1) != rhsr || (cu-cl+1) != rhsc ) {
+				throw new DMLRuntimeException("Invalid values for matrix indexing: "
+					+ "dimensions of the source matrix ["+rhsr+"x"+rhsc+"] "
+					+ "do not match the shape of the matrix specified by indices "
+					+ "["+(rl+1)+":"+(ru+1)+", "+(cl+1)+":"+(cu+1)+"] "
+					+ "(i.e., ["+(ru-rl+1)+"x"+(cu-cl+1)+"]).");
+			}
+		}
+	}
+
 	@Override
 	public final MatrixBlock slice(IndexRange ixrange, MatrixBlock ret) {
 		return slice(