Add support for From and To method conversions (#1117)

src/Riok.Mapperly.Abstractions/MappingConversionType.cs

@@ -30,7 +30,7 @@ public enum MappingConversionType
 
     /// <summary>
     /// If the source type is a <see cref="string"/>,
-    /// uses a a static visible method named `Parse` on the target type
+    /// uses a static visible method named `Parse` on the target type
     /// with a return type equal to the target type and a string as single parameter.
     /// </summary>
     ParseMethod = 1 << 3,
@@ -64,26 +64,26 @@ public enum MappingConversionType
 
     /// <summary>
     /// If the source is a <see cref="DateTime"/>
-    /// and the target is a DateOnly
+    /// and the target is a <c>DateOnly</c>
     /// uses the `FromDateTime` method on the target type with the source as single parameter.
     /// </summary>
     DateTimeToDateOnly = 1 << 8,
 
     /// <summary>
     /// If the source is a <see cref="DateTime"/>
-    /// and the target is a TimeOnly
+    /// and the target is a <c>TimeOnly</c>
     /// uses the `FromDateTime` method on the target type with the source as single parameter.
     /// </summary>
     DateTimeToTimeOnly = 1 << 9,
 
     /// <summary>
-    /// If the source and the target is a <see cref="IQueryable{T}"/>.
+    /// If the source and the target are a <see cref="IQueryable{T}"/>.
     /// Only uses object initializers and inlines the mapping code.
     /// </summary>
     Queryable = 1 << 10,
 
     /// <summary>
-    /// If the source and the target is an <see cref="IEnumerable{T}"/>
+    /// If the source and the target are an <see cref="IEnumerable{T}"/>
     /// Maps each element individually.
     /// </summary>
     Enumerable = 1 << 11,
@@ -115,10 +115,29 @@ public enum MappingConversionType
     Tuple = 1 << 15,
 
     /// <summary>
-    /// Allow using the underlying type of an enum to map from or to an enum type.
+    /// Allow using the underlying type of enum to map from or to an enum type.
     /// </summary>
     EnumUnderlyingType = 1 << 16,
 
+    /// <summary>
+    /// If the source type contains a `ToTarget` method other than `ToString`, use it
+    /// </summary>
+    ToTargetMethod = 1 << 17,
+
+    /// <summary>
+    /// If the source type contains a static `ToTarget` method
+    /// or the target type contains a static methods
+    /// `Create(TSource)`,
+    /// `CreateFrom(TSource)`,
+    /// `CreateFromTSource(TSource)`,
+    /// `From(TSource)`,
+    /// `FromTSource(TSource)`
+    /// or similar methods with <see langword="params"/> keyword, use it.
+    /// The exception is <see cref="DateTime"/> conversions,
+    /// which are enabled by separate options (<seealso cref="DateTimeToTimeOnly"/>, <seealso cref="DateTimeToDateOnly"/>).
+    /// </summary>
+    StaticConvertMethods = 1 << 18,
+
     /// <summary>
     /// Enables all supported conversions.
     /// </summary>

src/Riok.Mapperly/Descriptors/MappingBuilders/ConvertInstanceMethodMappingBuilder.cs

@@ -0,0 +1,66 @@
+using Microsoft.CodeAnalysis;
+using Riok.Mapperly.Abstractions;
+using Riok.Mapperly.Descriptors.Mappings;
+using Riok.Mapperly.Helpers;
+
+namespace Riok.Mapperly.Descriptors.MappingBuilders;
+
+public static class ConvertInstanceMethodMappingBuilder
+{
+    public static SourceObjectMethodMapping? TryBuildMapping(MappingBuilderContext ctx)
+    {
+        if (!ctx.IsConversionEnabled(MappingConversionType.ToTargetMethod))
+            return null;
+
+        var targetIsNullable = ctx.Target.NonNullable(out var nonNullableTarget);
+
+        // ignore `ToString` mapping for backward compatibility
+        if (nonNullableTarget.SpecialType == SpecialType.System_String)
+            return null;
+
+        foreach (var methodName in GetMappingMethodNames(ctx))
+        {
+            var methodCandidates = ctx
+                .SymbolAccessor.GetAllMethods(ctx.Source)
+                .Where(m =>
+                    string.Equals(m.Name, methodName, StringComparison.OrdinalIgnoreCase)
+                    && m is { IsStatic: false, ReturnsVoid: false, IsAsync: false, Parameters.Length: 0 }
+                )
+                .ToList();
+
+            // try to find method with equal nullability return type
+            var method = methodCandidates.Find(x => SymbolEqualityComparer.IncludeNullability.Equals(x.ReturnType, ctx.Target));
+            if (method is not null)
+                return new SourceObjectMethodMapping(ctx.Source, ctx.Target, method.Name);
+
+            if (!targetIsNullable)
+                continue;
+
+            // otherwise try to find method ignoring the nullability
+            method = methodCandidates.Find(x => SymbolEqualityComparer.Default.Equals(x.ReturnType, nonNullableTarget));
+
+            if (method is null)
+                continue;
+
+            return new SourceObjectMethodMapping(ctx.Source, ctx.Target, method.Name);
+        }
+
+        return null;
+    }
+
+    private static IEnumerable<string> GetMappingMethodNames(MappingBuilderContext ctx)
+    {
+        var nonNullableTarget = ctx.Target.NonNullable();
+        var hasKeyword = nonNullableTarget.HasKeyword(out var keywordName);
+        if (!nonNullableTarget.IsArrayType(out var arrayType))
+        {
+            var methodName = $"To{nonNullableTarget.Name}";
+            return hasKeyword ? [methodName, $"To{keywordName}"] : [methodName];
+        }
+
+        var nonNullableElementType = arrayType.ElementType.NonNullable();
+
+        var arrayMethodName = $"To{nonNullableElementType.Name}Array";
+        return hasKeyword ? [arrayMethodName, $"To{keywordName}Array"] : [arrayMethodName];
+    }
+}

src/Riok.Mapperly/Descriptors/MappingBuilders/ConvertStaticMethodMappingBuilder.cs

@@ -0,0 +1,169 @@
+using Microsoft.CodeAnalysis;
+using Riok.Mapperly.Abstractions;
+using Riok.Mapperly.Descriptors.Mappings;
+using Riok.Mapperly.Helpers;
+
+namespace Riok.Mapperly.Descriptors.MappingBuilders;
+
+public static class ConvertStaticMethodMappingBuilder
+{
+    public static StaticMethodMapping? TryBuildMapping(MappingBuilderContext ctx)
+    {
+        if (!IsConversionEnabled(ctx))
+            return null;
+
+        var targetIsNullable = ctx.Target.NonNullable(out var nonNullableTarget);
+
+        var allTargetMethods = ctx.SymbolAccessor.GetAllMethods(nonNullableTarget).ToList();
+
+        var mapping = TryGetStaticMethodMapping(
+            ctx.SymbolAccessor,
+            allTargetMethods,
+            GetTargetStaticMethodNames(ctx),
+            ctx.Source,
+            ctx.Target,
+            nonNullableTarget,
+            targetIsNullable
+        );
+
+        if (mapping is not null)
+        {
+            return mapping;
+        }
+
+        var allSourceMethods = ctx.SymbolAccessor.GetAllMethods(ctx.Source);
+
+        // collect also methods from source type generic argument, for example `TTarget ToTarget(List<A> source)`
+        if (ctx.Source is INamedTypeSymbol { TypeArguments.Length: 1 } namedTypeSymbol)
+        {
+            allSourceMethods = allSourceMethods.Concat(ctx.SymbolAccessor.GetAllMethods(namedTypeSymbol.TypeArguments[0]));
+        }
+
+        return TryGetStaticMethodMapping(
+            ctx.SymbolAccessor,
+            allSourceMethods.ToList(),
+            GetSourceStaticMethodNames(ctx),
+            ctx.Source,
+            ctx.Target,
+            nonNullableTarget,
+            targetIsNullable
+        );
+    }
+
+    private static bool IsConversionEnabled(MappingBuilderContext ctx)
+    {
+        //checks DateTime type for backward compatibility
+        return ctx.IsConversionEnabled(
+            IsDateTimeToDateOnlyConversion(ctx) ? MappingConversionType.DateTimeToDateOnly
+            : IsDateTimeToTimeOnlyConversion(ctx) ? MappingConversionType.DateTimeToTimeOnly
+            : MappingConversionType.StaticConvertMethods
+        );
+    }
+
+    private static bool IsDateTimeToDateOnlyConversion(MappingBuilderContext ctx)
+    {
+        return ctx.Source.SpecialType == SpecialType.System_DateTime
+            && ctx.Types.DateOnly != null
+            && ctx.Target is INamedTypeSymbol namedSymbol
+            && SymbolEqualityComparer.Default.Equals(namedSymbol, ctx.Types.DateOnly);
+    }
+
+    private static bool IsDateTimeToTimeOnlyConversion(MappingBuilderContext ctx)
+    {
+        return ctx.Source.SpecialType == SpecialType.System_DateTime
+            && ctx.Types.TimeOnly != null
+            && ctx.Target is INamedTypeSymbol namedSymbol
+            && SymbolEqualityComparer.Default.Equals(namedSymbol, ctx.Types.TimeOnly);
+    }
+
+    private static StaticMethodMapping? TryGetStaticMethodMapping(
+        SymbolAccessor symbolAccessor,
+        List<IMethodSymbol> allMethods,
+        IEnumerable<string> methodNames,
+        ITypeSymbol sourceType,
+        ITypeSymbol targetType,
+        ITypeSymbol nonNullableTargetType,
+        bool targetIsNullable
+    )
+    {
+        // Get all methods with a single parameter whose type is suitable for assignment to the source type, group them by name,
+        // and convert them to a dictionary whose key is the method name.
+        // The keys in the dictionary are compared case-insensitively to handle possible `Uint` vs `UInt` cases, etc.
+        var allMethodCandidates = allMethods
+            .Where(m => m is { IsStatic: true, ReturnsVoid: false, IsAsync: false, Parameters.Length: 1 })
+            .GroupBy(x => x.Name, x => x, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(x => x.Key, x => x.ToList(), StringComparer.OrdinalIgnoreCase);
+
+        foreach (var methodName in methodNames)
+        {
+            if (!allMethodCandidates.TryGetValue(methodName, out var candidates))
+                continue;
+
+            if (targetIsNullable)
+            {
+                continue;
+            }
+
+            var method = candidates.Find(x => symbolAccessor.ValidateSignature(x, nonNullableTargetType, sourceType));
+
+            if (method != null)
+                return new StaticMethodMapping(method);
+        }
+
+        return null;
+    }
+
+    private static IEnumerable<string> GetTargetStaticMethodNames(MappingBuilderContext ctx)
+    {
+        if (ctx.Source.IsArrayType(out var arrayType))
+        {
+            yield return $"CreateFrom{arrayType.ElementType.Name}Array";
+            yield return $"From{arrayType.ElementType.Name}Array";
+
+            if (!arrayType.ElementType.HasKeyword(out var keywordName))
+                yield break;
+
+            yield return $"CreateFrom{keywordName}Array";
+
+            yield return $"From{keywordName}Array";
+
+            yield return "FromArray";
+            yield return "CreateFromArray";
+            yield return "CreateFrom";
+            yield return "Create";
+            yield break;
+        }
+
+        yield return $"CreateFrom{ctx.Source.Name}";
+        yield return $"From{ctx.Source.Name}";
+
+        if (ctx.Source.HasKeyword(out var sourceKeyword))
+        {
+            yield return $"CreateFrom{sourceKeyword}";
+            yield return $"From{sourceKeyword}";
+        }
+
+        yield return "CreateFrom";
+        yield return "Create";
+    }
+
+    private static IEnumerable<string> GetSourceStaticMethodNames(MappingBuilderContext ctx)
+    {
+        var nonNullableTarget = ctx.Target.NonNullable();
+
+        yield return $"To{nonNullableTarget.Name}";
+
+        if (nonNullableTarget.HasKeyword(out var keywordName))
+            yield return $"To{keywordName}";
+
+        if (!nonNullableTarget.IsArrayType(out var arrayTypeSymbol))
+            yield break;
+
+        var nonNullableElementType = arrayTypeSymbol.ElementType.NonNullable();
+
+        yield return $"To{nonNullableElementType.Name}Array";
+
+        if (nonNullableElementType.HasKeyword(out var elementTypeName))
+            yield return $"To{elementTypeName}Array";
+    }
+}

src/Riok.Mapperly/Descriptors/MappingBuilders/MappingBuilder.cs

@@ -27,10 +27,10 @@ public class MappingBuilder(MappingCollection mappings, MapperDeclaration mapper
         StringToEnumMappingBuilder.TryBuildMapping,
         EnumToStringMappingBuilder.TryBuildMapping,
         EnumToEnumMappingBuilder.TryBuildMapping,
-        DateTimeToDateOnlyMappingBuilder.TryBuildMapping,
-        DateTimeToTimeOnlyMappingBuilder.TryBuildMapping,
         ExplicitCastMappingBuilder.TryBuildMapping,
         ToStringMappingBuilder.TryBuildMapping,
+        ConvertInstanceMethodMappingBuilder.TryBuildMapping,
+        ConvertStaticMethodMappingBuilder.TryBuildMapping,
         NewInstanceObjectMemberMappingBuilder.TryBuildMapping,
     ];