PY-21166 No inspection if unknown format code is used in formatted string

python/src/com/jetbrains/python/PyBundle.properties

@@ -391,6 +391,7 @@ INSP.too.many.args.for.fmt.string=Too many arguments for format string
 INSP.too.few.args.for.fmt.string=Too few arguments for format string
 INSP.incompatible.options=The format options in chunk "{0}" are incompatible
 INSP.unused.mapping = Mapping key "{0}" is unused
+INSP.unsupported.format.character=Unsupported format character ''{0}''
 
 # PyMethodOverridingInspection
 INSP.NAME.method.over=Method signature does not match signature of overridden method

python/src/com/jetbrains/python/inspections/PyStringFormatInspection.java

@@ -522,10 +522,15 @@ public class PyStringFormatInspection extends PyInspection {
         }
 
         final char conversionType = chunk.getConversionType();
-        if (NEW_STYLE_FORMAT_CONVERSIONS.containsKey(conversionType)) {
-          final String[] s = NEW_STYLE_FORMAT_CONVERSIONS.get(conversionType).split(" or ");
-          addTypes(types, Arrays.asList(s));
-          hasTypeOptions = true;
+        if (conversionType != Character.MIN_VALUE) {
+          if (NEW_STYLE_FORMAT_CONVERSIONS.containsKey(conversionType)) {
+            final String[] s = NEW_STYLE_FORMAT_CONVERSIONS.get(conversionType).split(" or ");
+            addTypes(types, Arrays.asList(s));
+            hasTypeOptions = true;
+          }
+          else {
+            registerProblem(myFormatExpression, PyBundle.message("INSP.unsupported.format.character", conversionType));
+          }
         }
 
         if (!types.isEmpty()) {

python/src/com/jetbrains/python/inspections/PyStringFormatParser.java

@@ -451,7 +451,7 @@ public class PyStringFormatParser {
         chunk.setPrecision(parseWhileCharacterInSet(DIGITS));
       }
 
-      if (isAtSet(NEW_STYLE_CONVERSION_TYPES)) {
+      if (myPos < end - 1) {
         chunk.setConversionType(myLiteral.charAt(myPos));
       }
     } 

python/testData/inspections/PyStringFormatInspection/UnsupportedFormatSpecifierNewStyleFormatting.py

@@ -0,0 +1 @@
+print(<warning descr="Unsupported format character 'q'">'{:+q}; {:+f}'</warning>.format(3.14, -3.14))

python/testSrc/com/jetbrains/python/inspections/PyStringFormatInspectionTest.java

@@ -203,7 +203,12 @@ public class PyStringFormatInspectionTest extends PyTestCase {
       }
     });
   }
-  
+
+  //PY-21166
+  public void testUnsupportedFormatSpecifierNewStyleFormatting() {
+    doTest();
+  }
+
   private void doTest() {
     myFixture.configureByFile(TEST_DIRECTORY + getTestName(false) + ".py");
     myFixture.enableInspections(PyStringFormatInspection.class);