1 files changed, 156 insertions, 0 deletions
diff --git a/python/mozboot/mozboot/mozconfig.py b/python/mozboot/mozboot/mozconfig.py
new file mode 100644
index 0000000000..a1ae4c8523
--- /dev/null
+++ b/python/mozboot/mozboot/mozconfig.py
@@ -0,0 +1,156 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import filecmp
+import os
+from pathlib import Path
+from typing import Union
+
+MOZ_MYCONFIG_ERROR = """
+The MOZ_MYCONFIG environment variable to define the location of mozconfigs
+is deprecated. If you wish to define the mozconfig path via an environment
+variable, use MOZCONFIG instead.
+""".strip()
+
+MOZCONFIG_LEGACY_PATH_ERROR = """
+You currently have a mozconfig at %s. This implicit location is no longer
+supported. Please move it to %s/.mozconfig or set an explicit path
+via the $MOZCONFIG environment variable.
+""".strip()
+
+DEFAULT_TOPSRCDIR_PATHS = (".mozconfig", "mozconfig")
+DEPRECATED_TOPSRCDIR_PATHS = ("mozconfig.sh", "myconfig.sh")
+DEPRECATED_HOME_PATHS = (".mozconfig", ".mozconfig.sh", ".mozmyconfig.sh")
+
+
+class MozconfigFindException(Exception):
+    """Raised when a mozconfig location is not defined properly."""
+
+
+class MozconfigBuilder(object):
+    def __init__(self):
+        self._lines = []
+
+    def append(self, block):
+        self._lines.extend([line.strip() for line in block.split("\n") if line.strip()])
+
+    def generate(self):
+        return "".join(line + "\n" for line in self._lines)
+
+
+def find_mozconfig(topsrcdir: Union[str, Path], env=os.environ):
+    """Find the active mozconfig file for the current environment.
+
+    This emulates the logic in mozconfig-find.
+
+    1) If ENV[MOZCONFIG] is set, use that
+    2) If $TOPSRCDIR/mozconfig or $TOPSRCDIR/.mozconfig exists, use it.
+    3) If both exist or if there are legacy locations detected, error out.
+
+    The absolute path to the found mozconfig will be returned on success.
+    None will be returned if no mozconfig could be found. A
+    MozconfigFindException will be raised if there is a bad state,
+    including conditions from #3 above.
+    """
+    topsrcdir = Path(topsrcdir)
+
+    # Check for legacy methods first.
+    if "MOZ_MYCONFIG" in env:
+        raise MozconfigFindException(MOZ_MYCONFIG_ERROR)
+
+    env_path = env.get("MOZCONFIG", None) or None
+
+    if env_path is not None:
+        env_path = Path(env_path)
+
+    if env_path is not None:
+        if not env_path.is_absolute():
+            potential_roots = [topsrcdir, Path.cwd()]
+            # Attempt to eliminate duplicates for e.g.
+            # self.topsrcdir == Path.cwd().
+            potential_roots_strings = set(str(p.resolve()) for p in potential_roots)
+            existing = [
+                root
+                for root in potential_roots_strings
+                if (Path(root) / env_path).exists()
+            ]
+            if len(existing) > 1:
+                # There are multiple files, but we might have a setup like:
+                #
+                # somedirectory/
+                #   srcdir/
+                #   objdir/
+                #
+                # MOZCONFIG=../srcdir/some/path/to/mozconfig
+                #
+                # and be configuring from the objdir.  So even though we
+                # have multiple existing files, they are actually the same
+                # file.
+                mozconfigs = [root / env_path for root in existing]
+                if not all(
+                    map(
+                        lambda p1, p2: filecmp.cmp(p1, p2, shallow=False),
+                        mozconfigs[:-1],
+                        mozconfigs[1:],
+                    )
+                ):
+                    raise MozconfigFindException(
+                        "MOZCONFIG environment variable refers to a path that "
+                        + "exists in more than one of "
+                        + ", ".join(potential_roots_strings)
+                        + ". Remove all but one."
+                    )
+            elif not existing:
+                raise MozconfigFindException(
+                    "MOZCONFIG environment variable refers to a path that "
+                    + "does not exist in any of "
+                    + ", ".join(potential_roots_strings)
+                )
+
+            env_path = existing[0] / env_path
+        elif not env_path.exists():  # non-relative path
+            raise MozconfigFindException(
+                "MOZCONFIG environment variable refers to a path that "
+                f"does not exist: {env_path}"
+            )
+
+        if not env_path.is_file():
+            raise MozconfigFindException(
+                "MOZCONFIG environment variable refers to a " f"non-file: {env_path}"
+            )
+
+    srcdir_paths = [topsrcdir / p for p in DEFAULT_TOPSRCDIR_PATHS]
+    existing = [p for p in srcdir_paths if p.is_file()]
+
+    if env_path is None and len(existing) > 1:
+        raise MozconfigFindException(
+            "Multiple default mozconfig files "
+            "present. Remove all but one. " + ", ".join(str(p) for p in existing)
+        )
+
+    path = None
+
+    if env_path is not None:
+        path = env_path
+    elif len(existing):
+        assert len(existing) == 1
+        path = existing[0]
+
+    if path is not None:
+        return Path.cwd() / path
+
+    deprecated_paths = [topsrcdir / s for s in DEPRECATED_TOPSRCDIR_PATHS]
+
+    home = env.get("HOME", None)
+    if home is not None:
+        home = Path(home)
+        deprecated_paths.extend([home / s for s in DEPRECATED_HOME_PATHS])
+
+    for path in deprecated_paths:
+        if path.exists():
+            raise MozconfigFindException(
+                MOZCONFIG_LEGACY_PATH_ERROR % (path, topsrcdir)
+            )
+
+    return None