Fix completions triggered on existing private identifier property access (#36191)

Author: andrewbranch

src/services/completions.ts

@@ -877,7 +877,7 @@ namespace ts.Completions {
 
         // Check if the caret is at the end of an identifier; this is a partial identifier that we want to complete: e.g. a.toS|
         // Skip this partial identifier and adjust the contextToken to the token that precedes it.
-        if (contextToken && position <= contextToken.end && (isIdentifier(contextToken) || isKeyword(contextToken.kind))) {
+        if (contextToken && position <= contextToken.end && (isIdentifierOrPrivateIdentifier(contextToken) || isKeyword(contextToken.kind))) {
             const start = timestamp();
             contextToken = findPrecedingToken(contextToken.getFullStart(), sourceFile, /*startNode*/ undefined)!; // TODO: GH#18217
             log("getCompletionData: Get previous token 2: " + (timestamp() - start));

tests/cases/fourslash/completionsECMAPrivateMember.ts

@@ -0,0 +1,21 @@
+/// <reference path="fourslash.ts" />
+
+// @target: esnext
+
+////class K {
+////  #value: number;
+////
+////  foo() {
+////     this.#va/**/
+////  }
+////}
+
+verify.completions({
+  marker: "",
+  exact: [{
+    name: "#value",
+    insertText: undefined
+  }, {
+    name: "foo"
+  }]
+});