PY-46178 Protect against illegal fragment expression in f-string-like completion

It's not enough to just prepend an arbitrary string with "f" to treat it like
a well-formed f-string. If its part following "IntellijIdeaRulezzz " placeholder
contains special characters, such as "&" in URLs, it can break parsing of
a generated fragment to the extent we are no longer able to recover a string
literal from it (it all gets treated as a single embedded expression).
Forcibly closing a started fragment with "} " seems sufficient to guard against
the subsequent string content.

GitOrigin-RevId: fe682511475b800f013ace5e6e52fca9286cd418

python/python-psi-impl/src/com/jetbrains/python/codeInsight/completion/PyFStringLikeCompletionContributor.java

@@ -3,7 +3,6 @@ package com.jetbrains.python.codeInsight.completion;
 import com.intellij.codeInsight.completion.*;
 import com.intellij.codeInsight.lookup.LookupElement;
 import com.intellij.codeInsight.lookup.LookupElementDecorator;
-import com.intellij.featureStatistics.FeatureUsageTracker;
 import com.intellij.openapi.editor.Document;
 import com.intellij.patterns.PsiElementPattern;
 import com.intellij.psi.PsiReference;
@@ -72,7 +71,12 @@ public class PyFStringLikeCompletionContributor extends CompletionContributor {
         if (prefixCannotStartReference) {
           return;
         }
-        PyExpression fString = PyUtil.createExpressionFromFragment("f" + stringElemText, stringLiteral.getParent());
+
+        String fStringText = new StringBuilder()
+          .append("f").append(stringElemText)
+          .insert(relOffset + 1 + CompletionUtilCore.DUMMY_IDENTIFIER.length(), "} ")
+          .toString();
+        PyExpression fString = PyUtil.createExpressionFromFragment(fStringText, stringLiteral.getParent());
         assert fString != null;
         PsiReference reference = fString.findReferenceAt(relOffset + 1);
         if (reference == null) {

python/testData/completion/fStringLikeCompletionInsideUrl.py

@@ -0,0 +1,2 @@
+city = "spb"
+foo = "https://weather.talkpython.fm/api/weather?city={<caret>&state=&country=&units=imperial"

python/testSrc/com/jetbrains/python/Py3CompletionTest.java

@@ -468,6 +468,14 @@ public class Py3CompletionTest extends PyTestCase {
     assertTrue(ContainerUtil.exists(variants, v -> v.getLookupString().equals("my_expr")));
   }
 
+  // PY-46178
+  public void testFStringLikeCompletionInsideUrl() {
+    final String testName = getTestName(true);
+    myFixture.configureByFile(testName + ".py");
+    myFixture.completeBasic();
+    assertContainsElements(myFixture.getLookupElementStrings(), "city");
+  }
+
   // PY-46056
   public void testImportCompletionHintForSameDirectoryModuleInOrdinaryPackage() {
     doTestVariantTailText("ordinaryPackage/sample.py", "logging", null);