Support build dependencies

Resolves: python-poetry#2789

poetry/console/commands/build.py

@@ -1,9 +1,9 @@
 from cleo import option
 
-from .env_command import EnvCommand
+from poetry.console.commands.installer_command import InstallerCommand
 
 
-class BuildCommand(EnvCommand):
+class BuildCommand(InstallerCommand):
 
     name = "build"
     description = "Builds a package, as a tarball and a wheel by default."
@@ -33,4 +33,11 @@ def handle(self):
         )
 
         builder = Builder(self.poetry)
-        builder.build(fmt)
+
+        executable = None
+        if self.poetry.package.build_requires:
+            # ensure build requirements are available if specified
+            self.installer.categories({"build"}).run()
+            executable = self.installer.env.python
+
+        builder.build(fmt, executable=executable)

poetry/installation/base_installer.py

@@ -1,4 +1,8 @@
 class BaseInstaller:
+    @property
+    def env(self):
+        return getattr(self, "_env", None)
+
     def install(self, package):
         raise NotImplementedError
 

poetry/installation/installer.py

@@ -1,3 +1,4 @@
+from typing import Iterable
 from typing import List
 from typing import Optional
 from typing import Union
@@ -11,6 +12,7 @@
 from poetry.repositories import Pool
 from poetry.repositories import Repository
 from poetry.repositories.installed_repository import InstalledRepository
+from poetry.utils.env import Env
 from poetry.utils.extras import get_extra_package_names
 from poetry.utils.helpers import canonicalize_name
 
@@ -47,10 +49,12 @@ def __init__(
         self._verbose = False
         self._write_lock = True
         self._dev_mode = True
+        self._build_mode = True
         self._execute_operations = True
         self._lock = False
 
         self._whitelist = []
+        self._categories = set()
 
         self._extras = []
 
@@ -66,6 +70,10 @@ def __init__(
 
         self._installed_repository = installed
 
+    @property
+    def env(self):  # type: () -> Env
+        return self._env
+
     @property
     def executor(self):
         return self._executor
@@ -132,6 +140,14 @@ def dev_mode(self, dev_mode=True):  # type: (bool) -> Installer
     def is_dev_mode(self):  # type: () -> bool
         return self._dev_mode
 
+    def build_mode(self, build_mode=True):  # type: (bool) -> Installer
+        self._build_mode = build_mode
+
+        return self
+
+    def is_build_mode(self):  # type: () -> bool
+        return self._build_mode or self._dev_mode
+
     def update(self, update=True):  # type: (bool) -> Installer
         self._update = update
 
@@ -163,6 +179,13 @@ def whitelist(self, packages):  # type: (dict) -> Installer
 
         return self
 
+    def categories(
+        self, categories=None
+    ):  # type: (Optional[Iterable[str]]) -> Installer
+        self._categories = {category for category in categories or []}
+
+        return self
+
     def extras(self, extras):  # type: (list) -> Installer
         self._extras = extras
 
@@ -241,6 +264,10 @@ def _do_install(self, local_repo):
             root = root.clone()
             del root.dev_requires[:]
 
+        if not self.is_build_mode():
+            root = root.clone()
+            del root.build_requires[:]
+
         if self._io.is_verbose():
             self._io.write_line("")
             self._io.write_line(
@@ -455,6 +482,8 @@ def _get_operations_from_lock(
                     is_installed = True
                     if locked.category == "dev" and not self.is_dev_mode():
                         ops.append(Uninstall(locked))
+                    elif locked.category == "build" and not self.is_build_mode():
+                        ops.append(Uninstall(locked))
                     elif locked.optional and locked.name not in extra_packages:
                         # Installed but optional and not requested in extras
                         ops.append(Uninstall(locked))
@@ -506,11 +535,19 @@ def _filter_operations(
                 if package.name not in extra_packages:
                     op.skip("Not required")
 
+            if self._categories and package.category not in self._categories:
+                op.skip("Category ({}) not enabled".format(package.category))
+
             # If the package is a dev package and dev packages
             # are not requested, we skip it
             if package.category == "dev" and not self.is_dev_mode():
                 op.skip("Dev dependencies not requested")
 
+            # If the package is a build package and build packages
+            # are not requested, we skip it
+            if package.category == "build" and not self.is_build_mode():
+                op.skip("Build dependencies not requested")
+
     def _get_extra_packages(self, repo):  # type: (Repository) -> List[str]
         """
         Returns all package names required by extras.

poetry/puzzle/solver.py

@@ -338,6 +338,8 @@ def _get_tags_for_package(self, package, graph, depth=0):
 
         if "main" in categories:
             category = "main"
+        elif "build" in categories:
+            category = "build"
         else:
             category = "dev"