Fix for empty JoinedStr Str parts in 3.6 & 3.7

Author: dflook

src/python_minifier/expression_printer.py

@@ -14,13 +14,13 @@ def __init__(self):
         self.unicode_literals = False
 
         self.precedences = {
-            'Lambda': 2,
-            'IfExp': 3,
+            'Lambda': 2,  # Lamdda
+            'IfExp': 3,  # IfExp
             'comprehension': 3.5,
-            'Or': 4,
+            'Or': 4,  # BoolOp
             'And': 5,
             'Not': 6,
-            'In': 7, 'NotIn': 7, 'Is': 7, 'IsNot': 7, 'Lt': 7, 'LtE': 7, 'Gt': 7, 'GtE': 7, 'NotEq': 7, 'Eq': 7,
+            'In': 7, 'NotIn': 7, 'Is': 7, 'IsNot': 7, 'Lt': 7, 'LtE': 7, 'Gt': 7, 'GtE': 7, 'NotEq': 7, 'Eq': 7,  # Compare
             'BitOr': 8,
             'BitXor': 9,
             'BitAnd': 10,
@@ -190,11 +190,18 @@ def visit_Dict(self, node):
 
             if k is None:
                 self.code += '**'
+
+                if 0 < self.precedence(v) <=7:
+                    self.code += '('
+                    self._expression(v)
+                    self.code += ')'
+                else:
+                    self._expression(v)
             else:
                 self._expression(k)
                 self.code += ':'
 
-            self._expression(v)
+                self._expression(v)
 
         self.code += '}'
 

src/python_minifier/f_string.py

@@ -104,7 +104,11 @@ def __str__(self):
         return min(candidates, key=len)
 
     def str_for(self, s, quote):
-        return str(MiniString(s, quote)).replace('{', '{{').replace('}', '}}')
+        mini_s =  str(MiniString(s, quote)).replace('{', '{{').replace('}', '}}')
+
+        if mini_s == '':
+            return '\\\n'
+        return mini_s
 
 
 class FormattedValue(ExpressionPrinter):

src/python_minifier/module_printer.py

@@ -1,4 +1,5 @@
 import ast
+import sys
 
 from .expression_printer import ExpressionPrinter
 
@@ -160,7 +161,14 @@ def visit_Return(self, node):
 
         self.token_break()
         self.code += 'return'
-        if node.value is not None:
+        if isinstance(node.value, ast.Tuple):
+            if sys.version_info < (3, 8) and hasattr(ast, 'Starred') and [n for n in node.value.elts if isinstance(n, ast.Starred)]:
+                self.code += '('
+                self._testlist(node.value)
+                self.code += ')'
+            else:
+                self._testlist(node.value)
+        elif node.value is not None:
             self._testlist(node.value)
         self.end_statement()
 

test/test_dict_expansion.py

@@ -0,0 +1,26 @@
+import ast
+import sys
+import pytest
+from python_minifier import unparse
+from python_minifier.ast_compare import compare_ast
+
+def test_dict_expanson():
+    if sys.version_info < (3, 5):
+        pytest.skip('dict expansion not allowed in python < 3.5')
+
+    source = [
+        r'{**a>>9}',
+        r'{**(a or b)}',
+        r'{**(a and b)}',
+        r'{**a+b}',
+        r'{**(lambda a:a)}',
+        r'{**(a<b)}',
+        r'{**(yield a())}',
+        r'{**(a if a else a)}'
+    ]
+
+    for expression in source:
+        expected_ast = ast.parse(expression)
+        minified = unparse(expected_ast)
+        compare_ast(expected_ast, ast.parse(minified))
+        assert expression == minified

test/test_empty_fstring.py

@@ -0,0 +1,19 @@
+import ast
+import sys
+import pytest
+from python_minifier import unparse
+from python_minifier.ast_compare import compare_ast
+
+def test_fstring_empty_str():
+    if sys.version_info < (3, 6):
+        pytest.skip('f-string expressions not allowed in python < 3.6')
+
+    source = r'''
+f"""\
+{fg_br}"""
+'''
+
+    print(source)
+    expected_ast = ast.parse(source)
+    actual_ast = unparse(expected_ast)
+    compare_ast(expected_ast, ast.parse(actual_ast))

test/test_iterable_unpacking.py

@@ -0,0 +1,22 @@
+import ast
+import sys
+import pytest
+from python_minifier import unparse
+from python_minifier.ast_compare import compare_ast
+
+def test_return():
+    if sys.version_info < (3, 0):
+        pytest.skip('Iterable unpacking in return not allowed in python < 3.0')
+
+    elif sys.version_info < (3, 8):
+        # Parenthesis are required
+        source = 'def a():return(True,*[False])'
+
+    else:
+        # Parenthesis not required
+        source = 'def a():return True,*[False]'
+
+    expected_ast = ast.parse(source)
+    minified = unparse(expected_ast)
+    compare_ast(expected_ast, ast.parse(minified))
+    assert source == minified