fix(40365): handle deprecated properties of merged interfaces (#51640)

Author: a-tarasyuk

src/compiler/checker.ts

@@ -2272,6 +2272,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function isDeprecatedSymbol(symbol: Symbol) {
+        if (length(symbol.declarations) > 1) {
+            const parentSymbol = getParentOfSymbol(symbol);
+            if (parentSymbol && parentSymbol.flags & SymbolFlags.Interface) {
+                return some(symbol.declarations, d => !!(getCombinedNodeFlags(d) & NodeFlags.Deprecated));
+            }
+        }
         return !!(getDeclarationNodeFlagsFromSymbol(symbol) & NodeFlags.Deprecated);
     }
 

tests/cases/fourslash/jsdocDeprecated_suggestion19.ts

@@ -0,0 +1,22 @@
+///<reference path="fourslash.ts" />
+
+////interface I {
+////    x: number;
+////    y: number;
+////}
+////interface I {
+////    /** @deprecated  */
+////    x: number;
+////}
+////const foo: I = { x: 1, y: 1 };
+////foo.[|x|];
+
+const [range] = test.ranges();
+verify.getSuggestionDiagnostics([
+    {
+        "code": 6385,
+        "message": "'x' is deprecated.",
+        "reportsDeprecated": true,
+        "range": range
+    },
+]);