Don't force getting body psi if null is predicted by stubs but allow it for resolve

We can't avoid loading AST in general, because there're no stubs for
expression bodies.

compiler/psi/src/org/jetbrains/kotlin/psi/KtNamedFunction.java

@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.psi.psiUtil.KtPsiUtilKt;
 import org.jetbrains.kotlin.psi.stubs.KotlinFunctionStub;
 import org.jetbrains.kotlin.psi.stubs.elements.KtStubElementTypes;
 import org.jetbrains.kotlin.psi.typeRefHelpers.TypeRefHelpersKt;
+import org.jetbrains.kotlin.util.AstLoadingFilter;
 
 import java.util.Collections;
 import java.util.List;
@@ -122,7 +123,14 @@ public class KtNamedFunction extends KtTypeParameterListOwnerStub<KotlinFunction
     @Override
     @Nullable
     public KtExpression getBodyExpression() {
-        return findChildByClass(KtExpression.class);
+        KotlinFunctionStub stub = getStub();
+        if (stub != null && !stub.hasBody()) {
+            return null;
+        }
+
+        return AstLoadingFilter.forceAllowTreeLoading(this.getContainingFile(), () ->
+                findChildByClass(KtExpression.class)
+        );
     }
 
     @Override

compiler/psi/src/org/jetbrains/kotlin/psi/KtPropertyAccessor.java

@@ -24,6 +24,7 @@ import org.jetbrains.annotations.Nullable;
 import org.jetbrains.kotlin.lexer.KtTokens;
 import org.jetbrains.kotlin.psi.stubs.KotlinPropertyAccessorStub;
 import org.jetbrains.kotlin.psi.stubs.elements.KtStubElementTypes;
+import org.jetbrains.kotlin.util.AstLoadingFilter;
 
 import java.util.Collections;
 import java.util.List;
@@ -86,7 +87,14 @@ public class KtPropertyAccessor extends KtDeclarationStub<KotlinPropertyAccessor
     @Nullable
     @Override
     public KtExpression getBodyExpression() {
-        return findChildByClass(KtExpression.class);
+        KotlinPropertyAccessorStub stub = getStub();
+        if (stub != null && !stub.hasBody()) {
+            return null;
+        }
+
+        return AstLoadingFilter.forceAllowTreeLoading(this.getContainingFile(), () ->
+                findChildByClass(KtExpression.class)
+        );
     }
 
     @Override