provider: allow fallback to installed packages

src/poetry/puzzle/provider.py

@@ -35,6 +35,7 @@
 from poetry.packages import DependencyPackage
 from poetry.packages.package_collection import PackageCollection
 from poetry.puzzle.exceptions import OverrideNeeded
+from poetry.repositories.exceptions import PackageNotFound
 from poetry.utils.helpers import download_file
 from poetry.vcs.git import Git
 
@@ -46,10 +47,12 @@
 
  from poetry.core.packages.dependency import Dependency
  from poetry.core.packages.package import Package
+ from poetry.core.packages.specification import PackageSpecification
  from poetry.core.semver.version_constraint import VersionConstraint
  from poetry.core.version.markers import BaseMarker
 
  from poetry.repositories import Pool
+ from poetry.repositories import Repository
  from poetry.utils.env import Env
 
 
@@ -124,6 +127,7 @@ def __init__(
  pool: Pool,
  io: Any,
  env: Env | None = None,
+ installed: Repository | None = None,
  ) -> None:
  self._package = package
  self._pool = pool
@@ -136,6 +140,7 @@ def __init__(
  self._deferred_cache: dict[Dependency, Package] = {}
  self._load_deferred = True
  self._source_root: Path | None = None
+ self._installed = installed
 
  @property
  def pool(self) -> Pool:
@@ -185,6 +190,36 @@ def validate_package_for_dependency(
  f" package's name: {package.name}"
  )
 
+ def search_for_installed_packages(
+ self,
+ specification: PackageSpecification,
+ ) -> list[Package]:
+ """
+ Search for installed packages, when available, that provides the given
+ specification.
+
+ This is useful when dealing with packages that are under development, not
+ published on package sources and/or only available via system installations.
+ """
+ if not self._installed:
+ return []
+
+ logger.debug(
+ "Falling back to installed packages to discover metadata for <c2>%s</>",
+ specification.complete_name,
+ )
+ packages = [
+ package
+ for package in self._installed.packages
+ if package.provides(specification)
+ ]
+ logger.debug(
+ "Found <c2>%d</> compatible packages for <c2>%s</>",
+ len(packages),
+ specification.complete_name,
+ )
+ return packages
+
  def search_for(
  self,
  dependency: (
@@ -227,6 +262,9 @@ def search_for(
  reverse=True,
  )
 
+ if not packages:
+ packages = self.search_for_installed_packages(dependency)
+
  return PackageCollection(dependency, packages)
 
  def search_for_vcs(self, dependency: VCSDependency) -> list[Package]:
@@ -478,15 +516,25 @@ def complete_package(self, package: DependencyPackage) -> DependencyPackage:
  "url",
  "git",
  }:
- package = DependencyPackage(
- package.dependency,
- self._pool.package(
- package.name,
- package.version.text,
- extras=list(package.dependency.extras),
- repository=package.dependency.source_name,
- ),
- )
+ try:
+ package = DependencyPackage(
+ package.dependency,
+ self._pool.package(
+ package.name,
+ package.version.text,
+ extras=list(package.dependency.extras),
+ repository=package.dependency.source_name,
+ ),
+ )
+ except PackageNotFound as e:
+ for pkg in self.search_for_installed_packages(package.dependency):
+ package = DependencyPackage(
+ package.dependency,
+ pkg,
+ )
+ break
+ else:
+ raise e from e
  requires = package.requires
  else:
  requires = package.requires

src/poetry/puzzle/solver.py

@@ -58,7 +58,9 @@ def __init__(
  self._io = io
 
  if provider is None:
- provider = Provider(self._package, self._pool, self._io)
+ provider = Provider(
+ self._package, self._pool, self._io, installed=installed
+ )
 
  self._provider = provider
  self._overrides: list[dict[DependencyPackage, dict[str, Dependency]]] = []

tests/puzzle/test_solver.py

@@ -87,7 +87,12 @@ def solver(
  io: NullIO,
 ) -> Solver:
  return Solver(
- package, pool, installed, locked, io, provider=Provider(package, pool, io)
+ package,
+ pool,
+ installed,
+ locked,
+ io,
+ provider=Provider(package, pool, io, installed=installed),
  )
 
 
@@ -174,6 +179,36 @@ def test_install_non_existing_package_fail(
  solver.solve()
 
 
+def test_install_unpublished_package_does_not_fail(
+ installed: InstalledRepository,
+ solver: Solver,
+ repo: Repository,
+ package: ProjectPackage,
+):
+ package.add_dependency(Factory.create_dependency("B", "1"))
+
+ package_a = get_package("A", "1.0")
+ package_b = get_package("B", "1")
+ package_b.add_dependency(Factory.create_dependency("A", "1.0"))
+
+ repo.add_package(package_a)
+ installed.add_package(package_b)
+
+ transaction = solver.solve()
+
+ check_solver_result(
+ transaction,
+ [
+ {"job": "install", "package": package_a},
+ {
+ "job": "install",
+ "package": package_b,
+ "skipped": True, # already installed
+ },
+ ],
+ )
+
+
 def test_solver_with_deps(solver: Solver, repo: Repository, package: ProjectPackage):
  package.add_dependency(Factory.create_dependency("A", "*"))