PY-21245 Handle quotes in lookup items inside multiline string literals better

Namely, allow lookup items that contain quotes in some cases if the
containing string literal is multiline, hence there is still a suitable
type of quotes to wrap injected string literal into.

The orignal error described in the issue has been fixed earlier as
part of other changes for PY-21161.

python/src/com/jetbrains/python/codeInsight/intentions/PyConvertToFStringIntention.java

@@ -355,7 +355,7 @@ public class PyConvertToFStringIntention extends PyBaseIntentionAction {
     if (adjusted == null) return false;
 
     newStringText.append(adjusted.getText());
-    final String quotedAttrsAndItems = quoteItemsInFragments(field, stringInfo.getSingleQuote());
+    final String quotedAttrsAndItems = quoteItemsInFragments(field, stringInfo);
     if (quotedAttrsAndItems == null) return false;
 
     newStringText.append(quotedAttrsAndItems);
@@ -396,7 +396,7 @@ public class PyConvertToFStringIntention extends PyBaseIntentionAction {
   }
 
   @Nullable
-  private static String quoteItemsInFragments(@NotNull PyNewStyleStringFormatParser.Field field, char hostStringQuote) {
+  private static String quoteItemsInFragments(@NotNull PyNewStyleStringFormatParser.Field field, @NotNull StringNodeInfo hostStringInfo) {
     List<String> escaped = new ArrayList<>();
     for (String part : field.getAttributesAndLookups()) {
       if (part.startsWith(".")) {
@@ -411,11 +411,17 @@ public class PyConvertToFStringIntention extends PyBaseIntentionAction {
           escaped.add(part);
           continue;
         }
-        final char quote = flipQuote(hostStringQuote);
-        if (indexText.indexOf(hostStringQuote) >= 0 || indexText.indexOf(quote) >= 0) {
-          return null;
+        final char originalQuote = hostStringInfo.getSingleQuote();
+        char targetQuote = flipQuote(originalQuote);
+        // there are no escapes inside the fragment, so the lookup key cannot contain 
+        // the host string quote unless it's a multiline string literal
+        if (indexText.indexOf(targetQuote) >= 0) {
+          if (!hostStringInfo.isTripleQuoted() || indexText.indexOf(originalQuote) >= 0) {
+            return null;
+          }
+          targetQuote = originalQuote;
         }
-        escaped.add("[" + quote + indexText + quote + "]");
+        escaped.add("[" + targetQuote + indexText + targetQuote + "]");
       }
     }
     return StringUtil.join(escaped, "");

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsAlternativeQuoteOfMultilineHost.py

@@ -0,0 +1 @@
+'''{x["]}'''.format(x=d)

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsAlternativeQuoteOfMultilineHost_after.py

@@ -0,0 +1 @@
+f'''{d['"']}'''

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsBothTypesOfQuotesInsideMultilineHost.py

@@ -0,0 +1,3 @@
+'''
+{0["']}
+'''.format(d)

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsBothTypesOfQuotesInsideMultilineHost_after.py

@@ -0,0 +1,3 @@
+'''
+{0["']}
+'''.format(d)

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsQuoteOfMultilineHost.py

@@ -0,0 +1 @@
+'''{x[']}'''.format(x=d)

python/testData/intentions/PyConvertToFStringIntentionTest/formatMethodIndexContainsQuoteOfMultilineHost_after.py

@@ -0,0 +1 @@
+f'''{d["'"]}'''

python/testSrc/com/jetbrains/python/intentions/PyConvertToFStringIntentionTest.java

@@ -94,11 +94,27 @@ public class PyConvertToFStringIntentionTest extends PyIntentionTestCase {
   public void testFormatMethodItemAccess() {
     doTest();
   }
-
+  
+  // PY-21245
   public void testFormatMethodIndexContainsHostAlternativeQuote() {
     doTest();
   }
   
+  // PY-21245
+  public void testFormatMethodIndexContainsQuoteOfMultilineHost() {
+    doTest();    
+  }
+  
+  // PY-21245
+  public void testFormatMethodIndexContainsAlternativeQuoteOfMultilineHost() {
+    doTest();    
+  }
+
+  // PY-21245
+  public void testFormatMethodIndexContainsBothTypesOfQuotesInsideMultilineHost() {
+    doTest();
+  }
+
   public void testFormatMethodIndexContainsBackslash() {
     doTest();
   }