Remove backtrack strategy options

src/resolvelib/reporters.py

@@ -61,5 +61,5 @@ def rejecting_candidate(
     def pinning(self, candidate: CT) -> None:
         """Called when adding a candidate to the potential solution."""
 
-    def fallback(self, from_: str, to: str) -> None:
-        """Called when falling back from one backtrack strategy to another."""
+    def fallback(self) -> None:
+        """Called when falling back from backjumping to backtracking."""

src/resolvelib/resolvers.py

@@ -31,9 +31,6 @@
 
 if TYPE_CHECKING:
     from .providers import Preference
-    from typing_extensions import Literal
-
-    BacktrackStrategy = Literal["backjump_fallback", "backjump", "backtrack"]
 
     class Result(NamedTuple, Generic[RT, CT, KT]):
         mapping: Mapping[KT, CT]
@@ -104,11 +101,10 @@ def __init__(
         self,
         provider: AbstractProvider[RT, CT, KT],
         reporter: BaseReporter[RT, CT, KT],
-        backtrack_strategy: BacktrackStrategy = "backjump_fallback",
     ) -> None:
         self._p = provider
         self._r = reporter
-        self._backtrack_strategy: BacktrackStrategy = backtrack_strategy
+        self._started_fallback = False
         self._fallback_states: Optional[list[State[RT, CT, KT]]] = None
         self._states: list[State[RT, CT, KT]] = []
 
@@ -295,10 +291,7 @@ def _backjump_iteration(
         incompatible_state = False
         name, candidate, broken_state = None, None, None
 
-        if (
-            self._backtrack_strategy == "backjump_fallback"
-            and self._fallback_states is None
-        ):
+        if self._fallback_states is None:
             fallback_states = [
                 State(
                     s.mapping.copy(),
@@ -330,11 +323,7 @@ def _backjump_iteration(
 
             # Backup states first time a backjump goes
             # further than a backtrack would have
-            if (
-                self._backtrack_strategy == "backjump_fallback"
-                and self._fallback_states is None
-                and backjump_count == 2
-            ):
+            if self._fallback_states is None and backjump_count == 2:
                 self._fallback_states = fallback_states
 
         if name is None or candidate is None or broken_state is None:
@@ -400,7 +389,7 @@ def _backjump(self, causes: list[RequirementInformation[RT, CT]]) -> bool:
 
             name, candidate, incompatibilities_from_broken = None, None, None
 
-            if self._backtrack_strategy in ("backjump", "backjump_fallback"):
+            if not self._started_fallback:
                 try:
                     (
                         name,
@@ -410,18 +399,15 @@ def _backjump(self, causes: list[RequirementInformation[RT, CT]]) -> bool:
                         causes=causes, incompatible_deps=incompatible_deps
                     )
                 except ResolutionImpossible:
-                    if (
-                        self._backtrack_strategy == "backjump"
-                        or self._fallback_states is None
-                    ):
+                    if self._fallback_states is None:
                         raise
 
                     # Backjumping failed but fallback to backtracking was requested
                     self._states = self._fallback_states
-                    self._backtrack_strategy = "backtrack"
-                    self._r.fallback("backjump_fallback", "backtrack")
+                    self._started_fallback = True
+                    self._r.fallback()
 
-            if self._backtrack_strategy == "backtrack":
+            if self._started_fallback:
                 (
                     name,
                     candidate,