[query] fix & improve pprint for hl.Struct (#12901)

CHANGELOG: `hl.Struct` now has a correct and useful implementation of
pprint.

For structs with keys that were not identifiers, we produced incorrect
`repr` output. For `pprint`, we just `pprint`'ed a dictionary (so you
cannot even tell that the object was an `hl.Struct`). This PR:

1. Fixes `hl.Struct.__str__` to use the kwargs or dictionary
representation based on whether the keys are Python identifiers.
2. Teaches `StructPrettyPrinter` to first try to `repr` the struct (this
is what the default pretty printer does)
3. Teaches `StructPrettyPrinter` to properly pretty print a struct as an
`hl.Struct` preferring the kwarg representation when appropriate.
4. Teaches `_same` to use pretty printing when showing differing
records.

hail/python/hail/table.py

@@ -3,6 +3,7 @@
 import pandas
 import numpy as np
 import pyspark
+import pprint
 from typing import Optional, Dict, Callable, Sequence, Union
 
 from hail.expr.expressions import Expression, StructExpression, \
@@ -3669,7 +3670,7 @@ def _same(self, other, tolerance=1e-6, absolute=False, reorder_fields=False):
 
         if not hl.eval(_values_similar(t[left_global_value], t[right_global_value], tolerance, absolute)):
             g = hl.eval(t.globals)
-            print(f'Table._same: globals differ: {g[left_global_value]}, {g[right_global_value]}')
+            print(f'Table._same: globals differ:\n{pprint.pformat(g[left_global_value])}\n{pprint.pformat(g[right_global_value])}')
             return False
 
         if not t.all(hl.is_defined(t[left_value]) & hl.is_defined(t[right_value])
@@ -3678,7 +3679,7 @@ def _same(self, other, tolerance=1e-6, absolute=False, reorder_fields=False):
             t = t.filter(~ _values_similar(t[left_value], t[right_value], tolerance, absolute))
             bad_rows = t.take(10)
             for r in bad_rows:
-                print(f'  Row mismatch at key={r._key}:\n    L: {r[left_value]}\n    R: {r[right_value]}')
+                print(f'  Row mismatch at key={r._key}:\n    Left:\n{pprint.pformat(r[left_value])}\n    Right:\n{pprint.pformat(r[right_value])}')
             return False
 
         return True

hail/python/hail/utils/struct.py

@@ -81,7 +81,17 @@ def __repr__(self):
         return str(self)
 
     def __str__(self):
-        return 'Struct({})'.format(', '.join('{}={}'.format(k, repr(v)) for k, v in self._fields.items()))
+        if all(k.isidentifier() for k in self._fields):
+            return (
+                'Struct('
+                + ', '.join(f'{k}={repr(v)}' for k, v in self._fields.items())
+                + ')'
+            )
+        return (
+            'Struct(**{'
+            + ', '.join(f'{repr(k)}: {repr(v)}' for k, v in self._fields.items())
+            + '})'
+        )
 
     def __eq__(self, other):
         return isinstance(other, Struct) and self._fields == other._fields
@@ -241,10 +251,50 @@ def to_dict(struct):
 
 
 class StructPrettyPrinter(pprint.PrettyPrinter):
-    def _format(self, obj, *args, **kwargs):
+    def _format(self, obj, stream, indent, allowance, context, level, *args, **kwargs):
         if isinstance(obj, Struct):
-            obj = to_dict(obj)
-        return _old_printer._format(self, obj, *args, **kwargs)
+            rep = self._repr(obj, context, level)
+            max_width = self._width - indent - allowance
+            if len(rep) <= max_width:
+                stream.write(rep)
+                return
+
+            stream.write('Struct(')
+            indent += len('Struct(')
+            if all(k.isidentifier() for k in obj):
+                n = len(obj.items())
+                for i, (k, v) in enumerate(obj.items()):
+                    is_first = i == 0
+                    is_last = i == n - 1
+
+                    if not is_first:
+                        stream.write(' ' * indent)
+                    stream.write(k)
+                    stream.write('=')
+                    this_indent = indent + len(k) + len('=')
+                    self._format(v, stream, this_indent, allowance, context, level, *args, **kwargs)
+                    if not is_last:
+                        stream.write(',\n')
+            else:
+                stream.write('**{')
+                indent += len('**{')
+                n = len(obj.items())
+                for i, (k, v) in enumerate(obj.items()):
+                    is_first = i == 0
+                    is_last = i == n - 1
+
+                    if not is_first:
+                        stream.write(' ' * indent)
+                    stream.write(repr(k))
+                    stream.write(': ')
+                    this_indent = indent + len(repr(k)) + len(': ')
+                    self._format(v, stream, this_indent, allowance, context, level, *args, **kwargs)
+                    if not is_last:
+                        stream.write(',\n')
+                stream.write('}')
+            stream.write(')')
+        else:
+            _old_printer._format(self, obj, stream, indent, allowance, context, level, *args, **kwargs)
 
 
 pprint.PrettyPrinter = StructPrettyPrinter  # monkey-patch pprint