TY: Infer types for const generic defaults

Author: mchernyavsky

src/main/grammars/RustParser.bnf

@@ -451,7 +451,8 @@ private DefaultTypeParameterType ::= '=' TypeReference { pin = 1 }
 ConstParameter ::= OuterAttr* const identifier TypeAscription DefaultConstParameter? {
   pin = 2
   implements = [ "org.rust.lang.core.psi.ext.RsGenericParameter"
-                 "org.rust.lang.core.psi.ext.RsOuterAttributeOwner" ]
+                 "org.rust.lang.core.psi.ext.RsOuterAttributeOwner"
+                 "org.rust.lang.core.psi.ext.RsInferenceContextOwner" ]
   mixin = "org.rust.lang.core.psi.ext.RsConstParameterImplMixin"
   stubClass = "org.rust.lang.core.stubs.RsConstParameterStub"
   elementTypeFactory = "org.rust.lang.core.stubs.StubImplementationsKt.factory"

src/main/kotlin/org/rust/ide/annotator/RsErrorAnnotator.kt

@@ -615,6 +615,7 @@ class RsErrorAnnotator : AnnotatorBase(), HighlightRangeExtension {
     }
 
     private fun checkConstParameter(holder: RsAnnotationHolder, constParameter: RsConstParameter) {
+        collectDiagnostics(holder, constParameter)
         checkConstGenerics(holder, constParameter)
         checkDuplicates(holder, constParameter)
     }

src/main/kotlin/org/rust/ide/inspections/RsDiagnosticBasedInspection.kt

@@ -14,6 +14,7 @@ abstract class RsDiagnosticBasedInspection : RsLocalInspectionTool() {
     override fun buildVisitor(holder: RsProblemsHolder, isOnTheFly: Boolean): RsVisitor = object : RsVisitor() {
         override fun visitFunction(o: RsFunction) = collectDiagnostics(holder, o)
         override fun visitConstant(o: RsConstant) = collectDiagnostics(holder, o)
+        override fun visitConstParameter(o: RsConstParameter) = collectDiagnostics(holder, o)
         override fun visitArrayType(o: RsArrayType) = collectDiagnostics(holder, o)
         override fun visitBaseType(o: RsBaseType) = collectDiagnostics(holder, o)
         override fun visitTraitRef(o: RsTraitRef) = collectDiagnostics(holder, o)

src/main/kotlin/org/rust/lang/core/psi/ext/RsInferenceContextOwner.kt

@@ -19,6 +19,7 @@ val RsInferenceContextOwner.body: RsElement?
     get() = when (this) {
         is RsArrayType -> expr
         is RsConstant -> expr
+        is RsConstParameter -> blockExpr
         is RsFunction -> block
         is RsVariantDiscriminant -> expr
         is RsExpressionCodeFragment -> expr

src/main/kotlin/org/rust/lang/core/types/infer/TypeInference.kt

@@ -204,6 +204,7 @@ class RsInferenceContext(
             else -> {
                 val (retTy, expr) = when (element) {
                     is RsConstant -> element.typeReference?.type to element.expr
+                    is RsConstParameter -> element.typeReference?.type to element.blockExpr
                     is RsArrayType -> TyInteger.USize.INSTANCE to element.expr
                     is RsVariantDiscriminant -> {
                         val enum = element.contextStrict<RsEnumItem>()

src/test/kotlin/org/rust/ide/inspections/typecheck/RsTypeCheckInspectionTest.kt

@@ -29,8 +29,9 @@ class RsTypeCheckInspectionTest : RsInspectionsTestBase(RsTypeCheckInspection::c
 
     fun `test typecheck in const argument`() = checkByText("""
         #![feature(const_generics)]
-        struct S<const N: usize>;
-        trait T<const N: usize> {
+        #![feature(const_generics_defaults)]
+        struct S<const N: usize = <error>{ 1u8 }</error>>;
+        trait T<const N: usize = <error>{ 1u8 }</error>> {
             fn foo<const N: usize>(&self) -> S<{ N }>;
         }
         impl T<<error>1u8</error>> for S<<error>1u8</error>> {