PY-31991 Formatter strips spaces around topmost expressions in f-strings fragments

Thus we forcibly remove them whenever they are added as a result of "Extract variable"
refactoring.

Probably we could add a dedicated formatter option for that in future.

python/src/com/jetbrains/python/formatter/PythonFormattingModelBuilder.java

@@ -17,7 +17,6 @@ package com.jetbrains.python.formatter;
 
 import com.intellij.formatting.*;
 import com.intellij.lang.ASTNode;
-import com.intellij.openapi.util.TextRange;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiFile;
 import com.intellij.psi.codeStyle.CodeStyleSettings;
@@ -113,6 +112,8 @@ public class PythonFormattingModelBuilder implements FormattingModelBuilderEx, C
       .between(COMMA, RBRACKET).spaceIf(commonSettings.SPACE_WITHIN_BRACKETS | commonSettings.SPACE_AFTER_COMMA)
       .withinPair(LBRACKET, RBRACKET).spaceIf(commonSettings.SPACE_WITHIN_BRACKETS)
 
+      .withinPair(FSTRING_FRAGMENT_START, FSTRING_FRAGMENT_END).spaces(0)
+
       .before(COLON).spaceIf(pySettings.SPACE_BEFORE_PY_COLON)
       .afterInside(LPAR, FROM_IMPORT_STATEMENT).spaces(0, pySettings.FROM_IMPORT_NEW_LINE_AFTER_LEFT_PARENTHESIS)
       .betweenInside(COMMA, RPAR, FROM_IMPORT_STATEMENT).spaceIf(commonSettings.SPACE_AFTER_COMMA,

python/testData/formatter/spacesAroundFStringFragmentExpressionStripped.py

@@ -0,0 +1 @@
+s = f'foo{   42 }bar'

python/testData/formatter/spacesAroundFStringFragmentExpressionStripped_after.py

@@ -0,0 +1 @@
+s = f'foo{42}bar'

python/testData/refactoring/introduceVariable/noExtraSpacesAroundFStringFragmentExpression.after.py

@@ -0,0 +1,2 @@
+a = 42
+s = f'foo{a}bar'

python/testData/refactoring/introduceVariable/noExtraSpacesAroundFStringFragmentExpression.py

@@ -0,0 +1 @@
+s = f'foo{<selection>42</selection>}bar'

python/testSrc/com/jetbrains/python/PyFormatterTest.java

@@ -928,6 +928,11 @@ public class PyFormatterTest extends PyTestCase {
   }
 
   public void testMultilineFStringExpressions() {
-    doTest();
+    runWithLanguageLevel(LanguageLevel.PYTHON36, this::doTest);
+  }
+
+  // PY-31991
+  public void testSpacesAroundFStringFragmentExpressionStripped() {
+    runWithLanguageLevel(LanguageLevel.PYTHON36, this::doTest);
   }
 }

python/testSrc/com/jetbrains/python/refactoring/PyIntroduceVariableTest.java

@@ -5,6 +5,7 @@ import com.intellij.psi.PsiElement;
 import com.intellij.refactoring.util.CommonRefactoringUtil;
 import com.intellij.testFramework.TestDataPath;
 import com.jetbrains.python.PythonFileType;
+import com.jetbrains.python.psi.LanguageLevel;
 import com.jetbrains.python.psi.PyCallExpression;
 import com.jetbrains.python.psi.PyExpression;
 import com.jetbrains.python.psi.PyFunction;
@@ -315,6 +316,11 @@ public class PyIntroduceVariableTest extends PyIntroduceTestCase {
     doTest();
   }
 
+  // PY-31991
+  public void testNoExtraSpacesAroundFStringFragmentExpression() {
+    runWithLanguageLevel(LanguageLevel.PYTHON36, this::doTest);
+  }
+
   @Override
   protected String getTestDataPath() {
     return super.getTestDataPath() + "/refactoring/introduceVariable";