Add specific message for type errors on dict displays (#3100)

This fixes #304, #1183, and #2538

Author: dmoisset

mypy/checkexpr.py

@@ -1745,7 +1745,7 @@ def visit_dict_expr(self, e: DictExpr) -> Type:
                 [None],
                 self.chk.named_generic_type('builtins.dict', [kt, vt]),
                 self.named_type('builtins.function'),
-                name='<list>',
+                name='<dict>',
                 variables=[ktdef, vtdef])
             rv = self.check_call(constructor, args, [nodes.ARG_POS] * len(args), e)[0]
         else:

mypy/messages.py

@@ -522,7 +522,13 @@ def incompatible_argument(self, n: int, m: int, callee: CallableType, arg_type:
             name = callee.name[1:-1]
             n -= 1
             msg = '{} item {} has incompatible type {}'.format(
-                name[0].upper() + name[1:], n, self.format_simple(arg_type))
+                name.title(), n, self.format_simple(arg_type))
+        elif callee.name == '<dict>':
+            name = callee.name[1:-1]
+            n -= 1
+            key_type, value_type = cast(TupleType, arg_type).items
+            msg = '{} entry {} has incompatible type {}: {}'.format(
+                name.title(), n, self.format_simple(key_type), self.format_simple(value_type))
         elif callee.name == '<list-comprehension>':
             msg = 'List comprehension has incompatible type List[{}]'.format(
                 strip_quotes(self.format(arg_type)))

test-data/unit/check-expressions.test

@@ -1522,8 +1522,8 @@ def g() -> Iterator[int]:
 [case testDictWithKeywordArgsOnly]
 from typing import Dict, Any
 d1 = dict(a=1, b=2) # type: Dict[str, int]
-d2 = dict(a=1, b='') # type: Dict[str, int] # E: List item 1 has incompatible type "Tuple[str, str]"
-d3 = dict(a=1) # type: Dict[int, int] # E: List item 0 has incompatible type "Tuple[str, int]"
+d2 = dict(a=1, b='') # type: Dict[str, int] # E: Dict entry 1 has incompatible type "str": "str"
+d3 = dict(a=1) # type: Dict[int, int] # E: Dict entry 0 has incompatible type "str": "int"
 d4 = dict(a=1, b=1)
 d4.xyz # E: Dict[str, int] has no attribute "xyz"
 d5 = dict(a=1, b='') # type: Dict[str, Any]

test-data/unit/check-modules.test

@@ -1359,7 +1359,7 @@ def do_something(dic: Row) -> None:
 def do_another() -> Row:
     return {}
 
-do_something({'good': 'bad'}) # E: List item 0 has incompatible type "Tuple[str, str]"
+do_something({'good': 'bad'}) # E: Dict entry 0 has incompatible type "str": "str"
 reveal_type(do_another()) # E: Revealed type is 'builtins.dict[builtins.str, builtins.int]'
 
 [file ex2a.py]

test-data/unit/pythoneval.test

@@ -1065,7 +1065,7 @@ d3.xyz # E
 d4 = dict(a=1, b='') # type: Dict[str, Any]
 result = dict(x=[], y=[]) # type: Dict[str, List[str]]
 [out]
-_program.py:3: error: List item 1 has incompatible type "Tuple[str, str]"
+_program.py:3: error: Dict entry 1 has incompatible type "str": "str"
 _program.py:5: error: Dict[str, int] has no attribute "xyz"
 
 [case testDefaultDict]
@@ -1097,7 +1097,7 @@ MyDDict(dict)[0]
 _program.py:6: error: Argument 1 to "defaultdict" has incompatible type List[_T]; expected Callable[[], str]
 _program.py:9: error: Invalid index type "str" for "dict"; expected type "int"
 _program.py:9: error: Incompatible types in assignment (expression has type "int", target has type "str")
-_program.py:19: error: List item 0 has incompatible type "Tuple[str, List[<uninhabited>]]"
+_program.py:19: error: Dict entry 0 has incompatible type "str": List[<uninhabited>]
 _program.py:23: error: Invalid index type "str" for "dict"; expected type "int"
 
 [case testNoSubcriptionOfStdlibCollections]