Kotlin: locate generated data-class copy params at their property

A data class's generated `copy(...)` has one value parameter per
primary-constructor property. The K1 frontend records each such
parameter (and its type accesses) at the source location of the
corresponding property; the K2 frontend leaves them with undefined
offsets, which the extractor emits as a `0:0:0:0` location.

This divergence is purely a K2 information regression: the richer K1
location is unambiguously better (it points at the real property in
source, enabling location-based queries), so we converge K2 onto K1
rather than the other way around.

Because K2 exposes no PSI back-mapping, the location cannot be
recomputed from source; instead we recover it from the IR. For a value
parameter of a `GENERATED_DATA_CLASS_MEMBER` function whose own offsets
are undefined, we look up the primary-constructor parameter at the same
index and reuse its location.

Guards keep the change surgical:
  - `vp.startOffset >= 0` bails out, so K1 (which already has real
    offsets) is untouched.
  - the origin must be `GENERATED_DATA_CLASS_MEMBER`.
  - the primary-ctor parameter name must match and carry real offsets,
    which restricts the remap to `copy`-style parameters and excludes
    members such as `equals(other)`.

Relearned both suites: only data-class `copy` parameter rows change
(K2 now matches K1). data-classes/PrintAst.expected becomes byte
-identical across suites; the residual diffs in methods/{exprs,
parameters}.expected are pre-existing, unrelated divergences.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -1329,6 +1329,35 @@ open class KotlinFileExtractor(
     private fun hasSynthesizedParameterNames(f: IrFunction) =
         f.descriptor.hasSynthesizedParameterNames()
 
+    /**
+     * Returns the location of the primary-constructor parameter corresponding to a generated
+     * data-class `copy` value parameter, or null if [vp] is not such a parameter.
+     *
+     * A data class's generated `copy(...)` has one value parameter per primary-constructor
+     * property, defaulting to the current value. K1 records these parameters at the source
+     * location of the corresponding property; K2 leaves them with undefined offsets (a
+     * `0:0:0:0` location). To keep the richer K1 information under both frontends, we recover
+     * the property location from the primary constructor via the IR.
+     *
+     * Guards ensure this only affects the K2 case (K1 parameters already carry real offsets)
+     * and only `copy`-style parameters (matched by name against the primary-constructor
+     * parameter at the same index), so members such as `equals(other)` are left untouched.
+     */
+    private fun getGeneratedDataClassCopyParamLocation(
+        vp: IrValueParameter,
+        idx: Int
+    ): Label<DbLocation>? {
+        if (vp.startOffset >= 0) return null
+        val fn = vp.parent as? IrFunction ?: return null
+        if (fn.origin != IrDeclarationOrigin.GENERATED_DATA_CLASS_MEMBER) return null
+        val ctorParam =
+            fn.parentClassOrNull?.primaryConstructor?.codeQlValueParameters?.getOrNull(idx)
+                ?: return null
+        if (ctorParam.name.asString() != vp.name.asString() || ctorParam.startOffset < 0)
+            return null
+        return tw.getLocation(ctorParam)
+    }
+
     private fun extractValueParameter(
         vp: IrValueParameter,
         parent: Label<out DbCallable>,
@@ -1340,7 +1369,10 @@ open class KotlinFileExtractor(
         locOverride: Label<DbLocation>? = null
     ): TypeResults {
         with("value parameter", vp) {
-            val location = locOverride ?: getLocation(vp, classTypeArgsIncludingOuterClasses)
+            val location =
+                locOverride
+                    ?: getGeneratedDataClassCopyParamLocation(vp, idx)
+                    ?: getLocation(vp, classTypeArgsIncludingOuterClasses)
             val maybeAlteredType =
                 (vp.parent as? IrFunction)?.let {
                     if (overridesCollectionsMethodWithAlteredParameterTypes(it))

java/ql/test-kotlin2/library-tests/data-classes/PrintAst.expected

@@ -17,11 +17,11 @@ dc.kt:
 #    0|     3: [Method] copy
 #    0|       3: [TypeAccess] ProtoMapValue
 #-----|       4: (Parameters)
-#    0|         0: [Parameter] bytes
-#    0|           0: [TypeAccess] byte[]
-#    0|         1: [Parameter] strs
-#    0|           0: [TypeAccess] String[]
-#    0|             0: [TypeAccess] String
+#    1|         0: [Parameter] bytes
+#    1|           0: [TypeAccess] byte[]
+#    1|         1: [Parameter] strs
+#    1|           0: [TypeAccess] String[]
+#    1|             0: [TypeAccess] String
 #    0|       5: [BlockStmt] { ... }
 #    0|         0: [ReturnStmt] return ...
 #    0|           0: [ClassInstanceExpr] new ProtoMapValue(...)

java/ql/test-kotlin2/library-tests/methods/exprs.expected

@@ -48,7 +48,6 @@
 | dataClass.kt:0:0:0:0 | String | TypeAccess |
 | dataClass.kt:0:0:0:0 | String | TypeAccess |
 | dataClass.kt:0:0:0:0 | String | TypeAccess |
-| dataClass.kt:0:0:0:0 | String | TypeAccess |
 | dataClass.kt:0:0:0:0 | boolean | TypeAccess |
 | dataClass.kt:0:0:0:0 | copy(...) | MethodCall |
 | dataClass.kt:0:0:0:0 | false | BooleanLiteral |
@@ -60,7 +59,6 @@
 | dataClass.kt:0:0:0:0 | int | TypeAccess |
 | dataClass.kt:0:0:0:0 | int | TypeAccess |
 | dataClass.kt:0:0:0:0 | int | TypeAccess |
-| dataClass.kt:0:0:0:0 | int | TypeAccess |
 | dataClass.kt:0:0:0:0 | new DataClass(...) | ClassInstanceExpr |
 | dataClass.kt:0:0:0:0 | other | VarAccess |
 | dataClass.kt:0:0:0:0 | other | VarAccess |
@@ -114,6 +112,7 @@
 | dataClass.kt:1:22:1:31 | int | TypeAccess |
 | dataClass.kt:1:22:1:31 | int | TypeAccess |
 | dataClass.kt:1:22:1:31 | int | TypeAccess |
+| dataClass.kt:1:22:1:31 | int | TypeAccess |
 | dataClass.kt:1:22:1:31 | this | ThisAccess |
 | dataClass.kt:1:22:1:31 | this.x | VarAccess |
 | dataClass.kt:1:22:1:31 | x | VarAccess |
@@ -125,6 +124,7 @@
 | dataClass.kt:1:34:1:46 | String | TypeAccess |
 | dataClass.kt:1:34:1:46 | String | TypeAccess |
 | dataClass.kt:1:34:1:46 | String | TypeAccess |
+| dataClass.kt:1:34:1:46 | String | TypeAccess |
 | dataClass.kt:1:34:1:46 | Unit | TypeAccess |
 | dataClass.kt:1:34:1:46 | this | ThisAccess |
 | dataClass.kt:1:34:1:46 | this | ThisAccess |

java/ql/test-kotlin2/library-tests/methods/parameters.expected

@@ -1,6 +1,6 @@
 | clinit.kt:3:1:3:20 | setTopLevelInt | clinit.kt:3:1:3:20 | <set-?> | 0 |
-| dataClass.kt:0:0:0:0 | copy | dataClass.kt:0:0:0:0 | x | 0 |
-| dataClass.kt:0:0:0:0 | copy | dataClass.kt:0:0:0:0 | y | 1 |
+| dataClass.kt:0:0:0:0 | copy | dataClass.kt:1:22:1:31 | x | 0 |
+| dataClass.kt:0:0:0:0 | copy | dataClass.kt:1:34:1:46 | y | 1 |
 | dataClass.kt:0:0:0:0 | copy$default | dataClass.kt:0:0:0:0 | p0 | 0 |
 | dataClass.kt:0:0:0:0 | copy$default | dataClass.kt:0:0:0:0 | p1 | 1 |
 | dataClass.kt:0:0:0:0 | copy$default | dataClass.kt:0:0:0:0 | p2 | 2 |