Cherry-pick PR microsoft#47500 into release-4.5

Component commits:
43c3f45 Modify debug assertion to avoid crashing on SyntaxList

9570a59 PR changes

e9a2355 More PR feedback

Author: jakebailey

src/services/utilities.ts

@@ -1304,7 +1304,7 @@ namespace ts {
 
                     if (lookInPreviousChild) {
                         // actual start of the node is past the position - previous token should be at the end of previous child
-                        const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ i, sourceFile);
+                        const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ i, sourceFile, n.kind);
                         return candidate && findRightmostToken(candidate, sourceFile);
                     }
                     else {
@@ -1320,7 +1320,7 @@ namespace ts {
             // the only known case is when position is at the end of the file.
             // Try to find the rightmost token in the file without filtering.
             // Namely we are skipping the check: 'position < node.end'
-            const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ children.length, sourceFile);
+            const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ children.length, sourceFile, n.kind);
             return candidate && findRightmostToken(candidate, sourceFile);
         }
     }
@@ -1339,19 +1339,21 @@ namespace ts {
             return n;
         }
 
-        const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ children.length, sourceFile);
+        const candidate = findRightmostChildNodeWithTokens(children, /*exclusiveStartPosition*/ children.length, sourceFile, n.kind);
         return candidate && findRightmostToken(candidate, sourceFile);
     }
 
     /**
      * Finds the rightmost child to the left of `children[exclusiveStartPosition]` which is a non-all-whitespace token or has constituent tokens.
      */
-    function findRightmostChildNodeWithTokens(children: Node[], exclusiveStartPosition: number, sourceFile: SourceFile): Node | undefined {
+    function findRightmostChildNodeWithTokens(children: Node[], exclusiveStartPosition: number, sourceFile: SourceFile, parentKind: SyntaxKind): Node | undefined {
         for (let i = exclusiveStartPosition - 1; i >= 0; i--) {
             const child = children[i];
 
             if (isWhiteSpaceOnlyJsxText(child)) {
-                Debug.assert(i > 0, "`JsxText` tokens should not be the first child of `JsxElement | JsxSelfClosingElement`");
+                if (i === 0 && (parentKind === SyntaxKind.JsxText || parentKind === SyntaxKind.JsxSelfClosingElement)) {
+                    Debug.fail("`JsxText` tokens should not be the first child of `JsxElement | JsxSelfClosingElement`");
+                }
             }
             else if (nodeHasTokens(children[i], sourceFile)) {
                 return children[i];

tests/cases/fourslash/quickInfoOnClosingJsx.ts

@@ -0,0 +1,8 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: foo.tsx
+////let x = <div>
+////    /*$*/</div >
+
+goTo.marker("$");
+verify.not.quickInfoExists();