feat(v1.7): conditional property assignment (Condition/SkipWhen)

docs/SPEC-v1.7-projection-and-conditional.md

@@ -7,7 +7,7 @@ v1.7 closes three AutoMapper-parity gaps surfaced by the [Duende.IdentityServer.
 | # | Feature | Issue | Effort | Status |
 |---|---------|-------|--------|--------|
 | 1 | Per-property LINQ projection (`SelectProperty`) | [#125](https://github.com/superyyrrzz/ForgeMap/issues/125) | Low | Planned |
-| 2 | Conditional property assignment (`Condition`, `SkipWhen`) | [#126](https://github.com/superyyrrzz/ForgeMap/issues/126) | Medium | Planned |
+| 2 | Conditional property assignment (`Condition`, `SkipWhen`) | [#126](https://github.com/superyyrrzz/ForgeMap/issues/126) | Medium | Implemented |
 | 3 | Entity↔primitive mapping (`[ExtractProperty]`, `[WrapProperty]`) | [#127](https://github.com/superyyrrzz/ForgeMap/issues/127) | Medium | Planned |
 
 Features 1 and 3 compose naturally: `SelectProperty` extracts a primitive from each element in a collection, while `[ExtractProperty]` / `[WrapProperty]` handle the single-element case. Both target the same join-table-entity pattern from opposite ends.

src/ForgeMap.Abstractions/ForgePropertyAttribute.cs

@@ -90,4 +90,24 @@ public ForgePropertyAttribute(string sourceProperty, string destinationProperty)
     /// on the same destination property.
     /// </summary>
     public string? SelectProperty { get; set; }
+
+    /// <summary>
+    /// Name of a predicate method on the forger class. Called with the source property value;
+    /// when it returns false, the destination assignment is skipped.
+    /// Signature: <c>bool MethodName(TSourceProperty value)</c>. Static or instance, any accessibility.
+    /// Mutually exclusive with <see cref="SkipWhen"/> on the same <c>[ForgeProperty]</c>.
+    /// Cannot be combined with <c>[ForgeFrom]</c> or <c>[ForgeWith]</c> on the same destination property.
+    /// Not supported on properties bound to a constructor parameter, an <c>init</c> setter, or a <c>required</c> member.
+    /// </summary>
+    public string? Condition { get; set; }
+
+    /// <summary>
+    /// Name of a predicate method on the forger class. Called with the source object;
+    /// when it returns true, the destination assignment is skipped.
+    /// Signature: <c>bool MethodName(TSource source)</c>. Static or instance, any accessibility.
+    /// Mutually exclusive with <see cref="Condition"/> on the same <c>[ForgeProperty]</c>.
+    /// Cannot be combined with <c>[ForgeFrom]</c> or <c>[ForgeWith]</c> on the same destination property.
+    /// Not supported on properties bound to a constructor parameter, an <c>init</c> setter, or a <c>required</c> member.
+    /// </summary>
+    public string? SkipWhen { get; set; }
 }

src/ForgeMap.Generator/AnalyzerReleases.Unshipped.md

@@ -10,6 +10,11 @@ FM0056 | ForgeMap | Error | SelectPropertyMemberNotFound
 FM0057 | ForgeMap | Error | SelectPropertyElementTypeIncompatible
 FM0058 | ForgeMap | Error | SelectPropertyConflictsWithConverter
 FM0059 | ForgeMap | Disabled | SelectPropertyApplied
+FM0060 | ForgeMap | Error | ConditionAndSkipWhenBothSet
+FM0061 | ForgeMap | Error | ConditionalPredicateInvalid
+FM0062 | ForgeMap | Error | ConditionalNotSupportedOnInitOrCtor
+FM0063 | ForgeMap | Error | ConditionalConflictsWithForgeFromOrWith
+FM0064 | ForgeMap | Disabled | ConditionalAssignmentApplied
 FM0072 | ForgeMap | Error | SelectPropertyConflictsWithForgeFromOrWith
 FM0073 | ForgeMap | Error | SelectPropertyDestinationNotEnumerable
 FM0075 | ForgeMap | Warning | SelectPropertyNotSupportedOnForgeInto

src/ForgeMap.Generator/DiagnosticDescriptors.cs

@@ -504,4 +504,44 @@ internal static class DiagnosticDescriptors
         category: Category,
         defaultSeverity: DiagnosticSeverity.Warning,
         isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor ConditionAndSkipWhenBothSet = new(
+        id: "FM0060",
+        title: "Condition and SkipWhen are mutually exclusive",
+        messageFormat: "Property '{0}' has both Condition and SkipWhen set on the same [ForgeProperty] — choose one",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor ConditionalPredicateInvalid = new(
+        id: "FM0061",
+        title: "Conditional predicate method not found or has wrong signature",
+        messageFormat: "Predicate method '{0}' for property '{1}' was not found on the forger class or has the wrong signature; expected: bool {0}({2})",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor ConditionalNotSupportedOnInitOrCtor = new(
+        id: "FM0062",
+        title: "Condition/SkipWhen cannot be applied to init, required, or constructor-bound properties",
+        messageFormat: "Condition/SkipWhen cannot be applied to property '{0}' because it is set via constructor or init/required. Use [ForgeFrom] to choose between alternative constructions, or drop init if you need conditional post-construction assignment.",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor ConditionalConflictsWithForgeFromOrWith = new(
+        id: "FM0063",
+        title: "Condition/SkipWhen conflicts with [ForgeFrom] / [ForgeWith]",
+        messageFormat: "Property '{0}' has Condition/SkipWhen and is also targeted by [ForgeFrom] or [ForgeWith] — choose one",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor ConditionalAssignmentApplied = new(
+        id: "FM0064",
+        title: "Conditional assignment applied for property",
+        messageFormat: "Conditional assignment applied for property '{0}' via '{1}'",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Info,
+        isEnabledByDefault: false);
 }