Add NoInferredDivision option

Author: Muximize

CodeGen/Generators/QuantityRelationsParser.cs

@@ -25,13 +25,16 @@ internal static class QuantityRelationsParser
         ///
         ///     The format of a relation definition is "Quantity.Unit operator Quantity.Unit = Quantity.Unit" (See examples below).
         ///     "double" can be used as a unitless operand.
-        ///     "1" can be used as the left operand to define inverse relations.
+        ///     "1" can be used as the result operand to define inverse relations.
+        ///
+        ///     Division relations are inferred from multiplication relations,
+        ///     but this can be skipped if the string ends with "NoInferredDivision".
         /// </summary>
         /// <example>
         /// [
-        ///     "Power.Watt = ElectricPotential.Volt * ElectricCurrent.Ampere",
-        ///     "Speed.MeterPerSecond = Length.Meter / Duration.Second",
-        ///     "ReciprocalLength.InverseMeter = 1 / Length.Meter"
+        ///   "1 = Length.Meter * ReciprocalLength.InverseMeter"
+        ///   "Power.Watt = ElectricPotential.Volt * ElectricCurrent.Ampere",
+        ///   "Mass.Kilogram = MassConcentration.KilogramPerCubicMeter * Volume.CubicMeter -- NoInferredDivision",
         /// ]
         /// </example>
         /// <param name="rootDir">Repository root directory.</param>
@@ -61,7 +64,7 @@ public static void ParseAndApplyRelations(string rootDir, Quantity[] quantities)
 
             // We can infer division relations from multiplication relations.
             relations.AddRange(relations
-                .Where(r => r.Operator is "*")
+                .Where(r => r is { Operator: "*", NoInferredDivision: false })
                 .Select(r => r with
                 {
                     Operator = "/",
@@ -74,9 +77,6 @@ public static void ParseAndApplyRelations(string rootDir, Quantity[] quantities)
                 .Where(r => r.LeftQuantity != r.RightQuantity)
                 .ToList());
 
-            // Remove inferred relation "MassConcentration = Mass / Volume" because it duplicates "Density = Mass / Volume"
-            relations.RemoveAll(r => r is { Operator: "/", ResultQuantity.Name: "MassConcentration", LeftQuantity.Name: "Mass", RightQuantity.Name: "Volume" });
-
             // We can infer TimeSpan relations from Duration relations.
             var timeSpanQuantity = pseudoQuantity with { Name = "TimeSpan" };
             relations.AddRange(relations
@@ -103,6 +103,18 @@ public static void ParseAndApplyRelations(string rootDir, Quantity[] quantities)
                 throw new UnitsNetCodeGenException($"Duplicate inferred relations:\n  {list}");
             }
 
+            var ambiguous = relations
+                .GroupBy(r => $"{r.LeftQuantity.Name} {r.Operator} {r.RightQuantity.Name}")
+                .Where(g => g.Count() > 1)
+                .Select(g => g.Key)
+                .ToList();
+
+            if (ambiguous.Any())
+            {
+                var list = string.Join("\n  ", ambiguous);
+                throw new UnitsNetCodeGenException($"Ambiguous inferred relations:\n  {list}\n\nHint: you could use NoInferredDivision in the definition file.");
+            }
+
             foreach (var quantity in quantities)
             {
                 var quantityRelations = new List<QuantityRelation>();
@@ -151,7 +163,7 @@ private static QuantityRelation ParseRelation(string relationString, IReadOnlyDi
         {
             var segments = relationString.Split(' ');
 
-            if (segments is not [_, "=", _, "*", _])
+            if (segments is not [_, "=", _, "*", _, ..])
             {
                 throw new Exception($"Invalid relation string: {relationString}");
             }
@@ -176,6 +188,7 @@ private static QuantityRelation ParseRelation(string relationString, IReadOnlyDi
 
             return new QuantityRelation
             {
+                NoInferredDivision = segments.Contains("NoInferredDivision"),
                 Operator = @operator,
                 LeftQuantity = leftQuantity,
                 LeftUnit = leftUnit,

CodeGen/JsonTypes/QuantityRelation.cs

@@ -7,6 +7,7 @@ namespace CodeGen.JsonTypes
 {
     internal record QuantityRelation : IComparable<QuantityRelation>
     {
+        public bool NoInferredDivision = false;
         public string Operator = null!;
 
         public Quantity LeftQuantity = null!;

Common/UnitRelations.json

@@ -37,7 +37,7 @@
   "Mass.Kilogram = AreaDensity.KilogramPerSquareMeter * Area.SquareMeter",
   "Mass.Kilogram = Density.KilogramPerCubicMeter * Volume.CubicMeter",
   "Mass.Kilogram = LinearDensity.KilogramPerMeter * Length.Meter",
-  "Mass.Kilogram = MassConcentration.KilogramPerCubicMeter * Volume.CubicMeter",
+  "Mass.Kilogram = MassConcentration.KilogramPerCubicMeter * Volume.CubicMeter -- NoInferredDivision",
   "Mass.Kilogram = MassFlow.KilogramPerSecond * Duration.Second",
   "Mass.Kilogram = MassFraction.DecimalFraction * Mass.Kilogram",
   "MassConcentration.KilogramPerCubicMeter = Molarity.MolePerCubicMeter * MolarMass.KilogramPerMole",