fixed Convert triple-quoted string: loses data in case of double quote inside the string and leads to syntax error

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

@@ -95,16 +95,8 @@ public class PyConvertTripleQuotedStringIntention extends BaseIntentionAction {
       subString = convertToValidSubString(trimmed.substring(0, trimmed.length() - 3), firstQuote);
     }
     else {
-      s = StringUtil.escapeStringCharacters(s);
       StringBuilder stringBuilder = new StringBuilder();
-      for (Character ch : s.toCharArray()) {
-        if (ch == firstQuote) {
-          stringBuilder.append("\\").append(firstQuote);
-        }
-        else {
-          stringBuilder.append(ch);
-        }
-      }
+      stringBuilder = StringUtil.escapeStringCharacters(s.length(), s, String.valueOf(firstQuote), true, stringBuilder);
       subString = stringBuilder.toString();
     }
     return subString;

python/testData/intentions/afterConvertTripleQuotedString1.py

@@ -0,0 +1,3 @@
+s = ("\n"
+     "my quote\" some text after it\n"
+)

python/testData/intentions/beforeConvertTripleQuotedString1.py

@@ -0,0 +1,3 @@
+s = """
+my q<caret>uote" some text after it
+"""

python/testSrc/com/jetbrains/python/PyIntentionTest.java

@@ -237,10 +237,15 @@ public class PyIntentionTest extends PyTestCase {
   public void testConvertVariadicParam() { //PY-2264
     doTest(PyBundle.message("INTN.convert.variadic.param"));
   }
+
   public void testConvertTripleQuotedString() { //PY-2697
     doTest(PyBundle.message("INTN.triple.quoted.string"));
   }
 
+  public void testConvertTripleQuotedString1() { //PY-7774
+    doTest(PyBundle.message("INTN.triple.quoted.string"));
+  }
+
   public void testTransformConditionalExpression() { //PY-3094
     doTest(PyBundle.message("INTN.transform.into.if.else.statement"));
   }