From b1b941b3195ac49849ccb461b61a0395431be2c2 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 17:17:30 +1300
Subject: [PATCH 1/7] Reimplementation of sorting units by dimensions

Adapt PR#1841 to the new Pint formatter.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/_format_helpers.py | 61 ++++++++++++++++++++-
 pint/delegates/formatter/full.py            | 16 +++++-
 pint/delegates/formatter/html.py            |  1 +
 pint/delegates/formatter/latex.py           |  4 ++
 pint/delegates/formatter/plain.py           |  1 +
 pint/testsuite/test_issues.py               | 49 +++++++++++++++++
 6 files changed, 128 insertions(+), 4 deletions(-)

diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index 2ed4ba985..868663b99 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -268,6 +268,61 @@ def format_compound_unit(
     return out
 
 
+def dim_sort(items: Iterable[tuple[str, Number]], registry: UnitRegistry):
+    """Sort a list of units by dimensional order (from `registry.formatter.dim_order`).
+
+    Parameters
+    ----------
+    items : tuple
+        a list of tuples containing (unit names, exponent values).
+    registry : UnitRegistry
+        the registry to use for looking up the dimensions of each unit.
+
+    Returns
+    -------
+    list
+        the list of units sorted by most significant dimension first.
+
+    Raises
+    ------
+    KeyError
+        If unit cannot be found in the registry.
+    """
+    
+    if registry is None:
+        return items
+    ret_dict = dict()
+    dim_order = registry.formatter.dim_order
+    for unit_name, unit_exponent in items:
+        cname = registry.get_name(unit_name)
+        if not cname:
+            continue
+        cname_dims = registry.get_dimensionality(cname)
+        if len(cname_dims) == 0:
+            cname_dims = {"[]": None}
+        dim_types = iter(dim_order)
+        while True:
+            try:
+                dim = next(dim_types)
+                if dim in cname_dims:
+                    if dim not in ret_dict:
+                        ret_dict[dim] = list()
+                    ret_dict[dim].append(
+                        (
+                            unit_name,
+                            unit_exponent,
+                        )
+                    )
+                    break
+            except StopIteration:
+                raise KeyError(
+                    f"Unit {unit_name} (aka {cname}) has no recognized dimensions"
+                )
+
+    ret = sum([ret_dict[dim] for dim in dim_order if dim in ret_dict], [])
+    return ret
+
+
 def formatter(
     items: Iterable[tuple[str, Number]],
     as_ratio: bool = True,
@@ -309,6 +364,8 @@ def formatter(
          (Default value = lambda x: f"{x:n}")
     sort : bool, optional
         True to sort the formatted units alphabetically (Default value = True)
+    sort_func : callable
+        If not None, `sort_func` returns its sorting of the formatted units
 
     Returns
     -------
@@ -320,14 +377,14 @@ def formatter(
     if sort is False:
         warn(
             "The boolean `sort` argument is deprecated. "
-            "Use `sort_fun` to specify the sorting function (default=sorted) "
+            "Use `sort_func` to specify the sorting function (default=sorted) "
             "or None to keep units in the original order."
         )
         sort_func = None
     elif sort is True:
         warn(
             "The boolean `sort` argument is deprecated. "
-            "Use `sort_fun` to specify the sorting function (default=sorted) "
+            "Use `sort_func` to specify the sorting function (default=sorted) "
             "or None to keep units in the original order."
         )
         sort_func = sorted
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index fae26d524..a8dc1ec56 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -11,9 +11,9 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Literal, Optional, Any
+from typing import TYPE_CHECKING, Callable, Literal, Optional, Any
 import locale
-from ...compat import babel_parse, Unpack
+from ...compat import babel_parse, Number, Unpack
 from ...util import iterable
 
 from ..._typing import Magnitude
@@ -38,6 +38,18 @@ class FullFormatter:
     _formatters: dict[str, Any] = {}
 
     default_format: str = ""
+    # TODO: This can be over-riden by the registry definitions file
+    dim_order = (
+        "[substance]",
+        "[mass]",
+        "[current]",
+        "[luminosity]",
+        "[length]",
+        "[]",
+        "[time]",
+        "[temperature]",
+    )
+    default_sort_func: Optional[Callable[Iterable[tuple[str, Number]]], Iterable[tuple[str, Number]]] = None
 
     locale: Optional[Locale] = None
     babel_length: Literal["short", "long", "narrow"] = "long"
diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index 3dc14330c..ea88fb13b 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -87,6 +87,7 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(x, unit._REGISTRY),
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/latex.py b/pint/delegates/formatter/latex.py
index aacf8cdf5..cf2b57848 100644
--- a/pint/delegates/formatter/latex.py
+++ b/pint/delegates/formatter/latex.py
@@ -173,6 +173,9 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
+        if unit._REGISTRY.formatter.default_sort_func:
+            # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
+            units = unit._REGISTRY.formatter.default_sort_func(units, unit._REGISTRY)
 
         preprocessed = {rf"\mathrm{{{latex_escape(u)}}}": p for u, p in units}
         formatted = formatter(
@@ -183,6 +186,7 @@ def format_unit(
             division_fmt=r"\frac[{}][{}]",
             power_fmt="{}^[{}]",
             parentheses_fmt=r"\left({}\right)",
+            sort_func=None,
         )
         return formatted.replace("[", "{").replace("]", "}")
 
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index 4b9616631..01c352bf9 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -269,6 +269,7 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(x, unit._REGISTRY),
         )
 
     def format_quantity(
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index 3db01fb4e..167d6bb4d 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1155,3 +1155,52 @@ def test_issues_1505():
     assert isinstance(
         ur.Quantity("m/s").magnitude, decimal.Decimal
     )  # unexpected fail (magnitude should be a decimal)
+
+
+def test_issues_1841(subtests):
+    import pint
+    from pint.delegates.formatter._format_helpers import dim_sort
+
+    ur = UnitRegistry()
+    ur.formatter.default_sort_func = dim_sort
+
+    for x, spec, result in (
+            (ur.Unit(UnitsContainer(hour=1,watt=1)), "P~", "W·h"),
+            (ur.Unit(UnitsContainer(ampere=1,volt=1)), "P~", "V·A"),
+            (ur.Unit(UnitsContainer(meter=1,newton=1)), "P~", "N·m"),
+    ):
+        with subtests.test(spec):
+            ur.default_format = spec
+            breakpoint()
+            assert f"{x}" == result, f"Failed for {spec}, {result}"
+
+
+@pytest.mark.xfail
+def test_issues_1841_xfail():
+    import pint
+    from pint import formatting as fmt
+    import pint.delegates.formatter._format_helpers
+    from pint.delegates.formatter._format_helpers import dim_sort
+
+    # sets compact display mode by default
+    ur = UnitRegistry()
+    ur.default_format = "~P"
+    ur.formatter.default_sort_func = dim_sort
+
+    q = ur.Quantity("2*pi radian * hour")
+
+    # Note that `radian` (and `bit` and `count`) are treated as dimensionless.
+    # And note that dimensionless quantities are stripped by this process,
+    # leading to errorneous output.  Suggestions?
+    breakpoint()
+    assert (
+        fmt.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
+        == "radian * hour"
+    )
+    assert (
+        fmt.format_unit(q.u._units, spec="", registry=ur, sort_dims=False)
+        == "hour * radian"
+    )
+
+    # this prints "2*pi hour * radian", not "2*pi radian * hour" unless sort_dims is True
+    # print(q)

From f6fbcc0fb428cf479f24aa5e9b010b05bf8eb3e8 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 17:25:06 +1300
Subject: [PATCH 2/7] Fix up pre-commit formatting

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 CHANGES                                     | 4 +++-
 pint/delegates/formatter/_format_helpers.py | 2 +-
 pint/delegates/formatter/full.py            | 6 ++++--
 pint/delegates/formatter/html.py            | 4 +++-
 pint/delegates/formatter/plain.py           | 4 +++-
 pint/testsuite/test_issues.py               | 9 +++------
 6 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/CHANGES b/CHANGES
index 6b1d0484e..c65d1f1d0 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,7 +4,9 @@ Pint Changelog
 0.24 (unreleased)
 -----------------
 
-- Nothing changed yet.
+- Add `dim_sort` function to _formatter_helpers.
+- Add `dim_order` and `default_sort_func` properties to FullFormatter.
+  (PR #????, fixes Issue #1841)
 
 
 0.23 (2023-12-08)
diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index 868663b99..a736c8d5f 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -288,7 +288,7 @@ def dim_sort(items: Iterable[tuple[str, Number]], registry: UnitRegistry):
     KeyError
         If unit cannot be found in the registry.
     """
-    
+
     if registry is None:
         return items
     ret_dict = dict()
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index a8dc1ec56..5864809b3 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -11,7 +11,7 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Callable, Literal, Optional, Any
+from typing import TYPE_CHECKING, Callable, Iterable, Literal, Optional, Any
 import locale
 from ...compat import babel_parse, Number, Unpack
 from ...util import iterable
@@ -49,7 +49,9 @@ class FullFormatter:
         "[time]",
         "[temperature]",
     )
-    default_sort_func: Optional[Callable[Iterable[tuple[str, Number]]], Iterable[tuple[str, Number]]] = None
+    default_sort_func: Optional[
+        Callable[Iterable[tuple[str, Number]]], Iterable[tuple[str, Number]]
+    ] = None
 
     locale: Optional[Locale] = None
     babel_length: Literal["short", "long", "narrow"] = "long"
diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index ea88fb13b..cc7d9ad07 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -87,7 +87,9 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(x, unit._REGISTRY),
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            ),
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index 01c352bf9..37150f9d2 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -269,7 +269,9 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(x, unit._REGISTRY),
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            ),
         )
 
     def format_quantity(
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index 167d6bb4d..7917b891a 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1158,16 +1158,15 @@ def test_issues_1505():
 
 
 def test_issues_1841(subtests):
-    import pint
     from pint.delegates.formatter._format_helpers import dim_sort
 
     ur = UnitRegistry()
     ur.formatter.default_sort_func = dim_sort
 
     for x, spec, result in (
-            (ur.Unit(UnitsContainer(hour=1,watt=1)), "P~", "W·h"),
-            (ur.Unit(UnitsContainer(ampere=1,volt=1)), "P~", "V·A"),
-            (ur.Unit(UnitsContainer(meter=1,newton=1)), "P~", "N·m"),
+        (ur.Unit(UnitsContainer(hour=1, watt=1)), "P~", "W·h"),
+        (ur.Unit(UnitsContainer(ampere=1, volt=1)), "P~", "V·A"),
+        (ur.Unit(UnitsContainer(meter=1, newton=1)), "P~", "N·m"),
     ):
         with subtests.test(spec):
             ur.default_format = spec
@@ -1177,9 +1176,7 @@ def test_issues_1841(subtests):
 
 @pytest.mark.xfail
 def test_issues_1841_xfail():
-    import pint
     from pint import formatting as fmt
-    import pint.delegates.formatter._format_helpers
     from pint.delegates.formatter._format_helpers import dim_sort
 
     # sets compact display mode by default

From 65fd12c832654a32216deb0ac726e3854d2fa77d Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 17:25:58 +1300
Subject: [PATCH 3/7] Update CHANGES

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 CHANGES | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index c65d1f1d0..048765ec0 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6,7 +6,7 @@ Pint Changelog
 
 - Add `dim_sort` function to _formatter_helpers.
 - Add `dim_order` and `default_sort_func` properties to FullFormatter.
-  (PR #????, fixes Issue #1841)
+  (PR #1926, fixes Issue #1841)
 
 
 0.23 (2023-12-08)

From 45515865cc446ea4c7107d9d9f3ef4b3f6ed99db Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 19:54:48 +1300
Subject: [PATCH 4/7] Update test_issues.py

Remove `breakpoint`s that should have been linted out by pre-commit.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/testsuite/test_issues.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index 7917b891a..f23c1bb84 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1170,7 +1170,6 @@ def test_issues_1841(subtests):
     ):
         with subtests.test(spec):
             ur.default_format = spec
-            breakpoint()
             assert f"{x}" == result, f"Failed for {spec}, {result}"
 
 
@@ -1189,7 +1188,6 @@ def test_issues_1841_xfail():
     # Note that `radian` (and `bit` and `count`) are treated as dimensionless.
     # And note that dimensionless quantities are stripped by this process,
     # leading to errorneous output.  Suggestions?
-    breakpoint()
     assert (
         fmt.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
         == "radian * hour"

From 7b9bc340b3db1ed49ea26d98fa89875efc3c8dde Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 21:02:23 +1300
Subject: [PATCH 5/7] Ensure called `default_sort_func` is not None

It would be easier to just default to `sorted` instead of `None`, but since `None` is an option, we have to test for it anyway.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/html.py  | 10 +++++++---
 pint/delegates/formatter/plain.py | 10 +++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index cc7d9ad07..98329bcca 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -78,6 +78,12 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
+        if unit._REGISTRY.formatter.default_sort_func is not None:
+            sort_func = lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            )
+        else:
+            sort_func = None
 
         return formatter(
             units,
@@ -87,9 +93,7 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=sort_func,
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index 37150f9d2..850e2eab5 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -259,6 +259,12 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
+        if unit._REGISTRY.formatter.default_sort_func is not None:
+            sort_func = lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            )
+        else:
+            sort_func = None
 
         return formatter(
             units,
@@ -269,9 +275,7 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=sort_func,
         )
 
     def format_quantity(

From a47b5e92d206ececae9e542b1c82a9fc061d3e83 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Tue, 23 Jan 2024 22:46:28 +1300
Subject: [PATCH 6/7] Fix default_sort_func

The default sort function needs to be able to handle a registry passed to it, so to make `sorted` the default behavior, we have to create a lambda that strips the registry parameter before calling `sorted`.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/full.py  | 14 +++++++++++---
 pint/delegates/formatter/html.py  | 11 +++--------
 pint/delegates/formatter/latex.py |  5 ++---
 pint/delegates/formatter/plain.py | 11 +++--------
 4 files changed, 19 insertions(+), 22 deletions(-)

diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index 5864809b3..98f22fdb6 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -24,7 +24,12 @@
 from ._to_register import REGISTERED_FORMATTERS
 
 if TYPE_CHECKING:
-    from ...facets.plain import PlainQuantity, PlainUnit, MagnitudeT
+    from ...facets.plain import (
+        GenericPlainRegistry,
+        PlainQuantity,
+        PlainUnit,
+        MagnitudeT,
+    )
     from ...facets.measurement import Measurement
     from ...compat import Locale
 
@@ -50,8 +55,11 @@ class FullFormatter:
         "[temperature]",
     )
     default_sort_func: Optional[
-        Callable[Iterable[tuple[str, Number]]], Iterable[tuple[str, Number]]
-    ] = None
+        Callable[
+            [Iterable[tuple[str, Number]], GenericPlainRegistry],
+            Iterable[tuple[str, Number]],
+        ]
+    ] = lambda self, x, registry: sorted(x)
 
     locale: Optional[Locale] = None
     babel_length: Literal["short", "long", "narrow"] = "long"
diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index 98329bcca..024a8c052 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -78,13 +78,6 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
-        if unit._REGISTRY.formatter.default_sort_func is not None:
-            sort_func = lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            )
-        else:
-            sort_func = None
-
         return formatter(
             units,
             as_ratio=True,
@@ -93,7 +86,9 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
-            sort_func=sort_func,
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            ),
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/latex.py b/pint/delegates/formatter/latex.py
index cf2b57848..fcf2494d3 100644
--- a/pint/delegates/formatter/latex.py
+++ b/pint/delegates/formatter/latex.py
@@ -173,9 +173,8 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
-        if unit._REGISTRY.formatter.default_sort_func:
-            # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
-            units = unit._REGISTRY.formatter.default_sort_func(units, unit._REGISTRY)
+        # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
+        units = unit._REGISTRY.formatter.default_sort_func(units, unit._REGISTRY)
 
         preprocessed = {rf"\mathrm{{{latex_escape(u)}}}": p for u, p in units}
         formatted = formatter(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index 850e2eab5..b6ce3c372 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -259,13 +259,6 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
-        if unit._REGISTRY.formatter.default_sort_func is not None:
-            sort_func = lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            )
-        else:
-            sort_func = None
-
         return formatter(
             units,
             as_ratio=True,
@@ -275,7 +268,9 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-            sort_func=sort_func,
+            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
+                x, unit._REGISTRY
+            ),
         )
 
     def format_quantity(

From 32f543dd3f884f82d86454781f342d7c52cff16f Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Wed, 24 Jan 2024 09:36:45 +1300
Subject: [PATCH 7/7] Refactor sort_func into `format_compound_unit`

This is a much more logical place to put it.  Note that the default formatters (plain, html, latex) all now call `formatter` with sort_func=None so that we don't accidentally use `sorted` as a default argument.  But those who call `formatter` directly for their own purposes can call with a sort_func of their choosing that will do what they want it to do.

This also fixes a latent bug where we failed to call `sort_func` in one of the paths of `plain.py`.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/_format_helpers.py | 3 +++
 pint/delegates/formatter/html.py            | 4 +---
 pint/delegates/formatter/latex.py           | 2 --
 pint/delegates/formatter/plain.py           | 6 +++---
 4 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index a736c8d5f..ca9e86a1b 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -265,6 +265,9 @@ def format_compound_unit(
     if locale is not None:
         out = localized_form(out, use_plural, length or "long", locale)
 
+    if registry:
+        out = registry.formatter.default_sort_func(out, registry)
+
     return out
 
 
diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index 024a8c052..773cd87ae 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -86,9 +86,7 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=None,
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/latex.py b/pint/delegates/formatter/latex.py
index fcf2494d3..a5df38ef3 100644
--- a/pint/delegates/formatter/latex.py
+++ b/pint/delegates/formatter/latex.py
@@ -173,8 +173,6 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
-        # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
-        units = unit._REGISTRY.formatter.default_sort_func(units, unit._REGISTRY)
 
         preprocessed = {rf"\mathrm{{{latex_escape(u)}}}": p for u, p in units}
         formatted = formatter(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index b6ce3c372..31b47bd95 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -77,6 +77,7 @@ def format_unit(
             division_fmt=" / ",
             power_fmt="{} ** {}",
             parentheses_fmt=r"({})",
+            sort_func=None,
         )
 
     def format_quantity(
@@ -175,6 +176,7 @@ def format_unit(
             division_fmt="/",
             power_fmt="{}**{}",
             parentheses_fmt=r"({})",
+            sort_func=None,
         )
 
     def format_quantity(
@@ -268,9 +270,7 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=None,
         )
 
     def format_quantity(