global: move license annotation to extensions entry

Having it in links implied the existence of a separate library file that
was linked against. This isn't always true, including on Windows where
the object files for the library can be compiled into the main Python
binary directly.

Author: indygreg

README.rst

@@ -359,6 +359,33 @@ extensions
       The string value may be ``NULL``, which may need special handling by
       consumers.
 
+   licenses
+      Array of strings containing the license shortname identifiers from the
+      SPDX license list (https://spdx.org/licenses/).
+
+      If this field is missing, licenses are unknown. Empty array denotes no known
+      licenses.
+
+      The license applies to additional libraries needed by this extension, not
+      the extension itself, as extensions should be licensed the same as the
+      Python distribution.
+
+      (Version 2 or above only.)
+
+   license_path
+      Paths to text files containing the licenses for this extension.
+
+      (Version 2 or above only.)
+
+   license_public_domain
+      Bool indicating that the license for the extension is in the public
+      domain.
+
+      There is no SPDX identifier for public domain. And we want to be explicit
+      about something being in the public domain because of the legal implications.
+
+      (Version 2 or above only.)
+
    links
       An array of linking requirement maps. (See below for data format.)
 
@@ -399,25 +426,3 @@ system
 
    System libraries are typically passed into the linker by name only and
    found using default library search paths.
-
-licenses
-   Array of strings containing the license shortname identifiers from the
-   SPDX license list (https://spdx.org/licenses/).
-
-   If this field is missing, licenses are unknown. Empty array denotes no known
-   licenses.
-
-   (Version 2 or above only.)
-
-license_path
-   Path to a text file containing the license for this library.
-
-   (Version 2 or above only.)
-
-license_public_domain
-   Bool indicating that the library is in the public domain.
-
-   There is no SPDX identifier for public domain. And we want to be explicit
-   about something being in the public domain because of the legal implications.
-
-   (Version 2 or above only.)

cpython-linux/build.py

@@ -25,7 +25,7 @@
     DOWNLOADS,
 )
 from pythonbuild.utils import (
-    add_license_to_link_entry,
+    add_licenses_to_extension_entry,
     download_entry,
 )
 
@@ -544,23 +544,24 @@ def process_setup_line(line, variant=None):
                     'path_static': 'build/lib/lib%s.a' % libname,
                 }
 
-                add_license_to_link_entry(entry)
-
                 links.append(entry)
             else:
                 links.append({
                     'name': libname,
                     'system': True,
                 })
 
-        bi['extensions'].setdefault(extension, []).append({
+        entry = {
             'in_core': False,
             'init_fn': 'PyInit_%s' % extension,
             'links': links,
             'objs': objs,
             'variant': d['variant'],
-        })
+        }
+
+        add_licenses_to_extension_entry(entry)
 
+        bi['extensions'].setdefault(extension, []).append(entry)
 
     found_start = False
 

cpython-macos/build.py

@@ -22,7 +22,7 @@
     DOWNLOADS,
 )
 from pythonbuild.utils import (
-    add_license_to_link_entry,
+    add_licenses_to_extension_entry,
     create_tar_from_directory,
     download_entry,
     extract_tar_to_directory,
@@ -244,22 +244,24 @@ def process_setup_line(line):
                     'path_static': 'build/lib/lib%s.a' % libname,
                 }
 
-                add_license_to_link_entry(entry)
-
                 links.append(entry)
             else:
                 links.append({
                     'name': libname,
                     'system': True,
                 })
 
-        bi['extensions'][extension] = [{
+        entry = {
             'in_core': False,
             'init_fn': 'PyInit_%s' % extension,
             'links': links,
             'objs': objs,
             'variant': 'default',
-        }]
+        }
+
+        add_licenses_to_extension_entry(entry)
+
+        bi['extensions'][extension] = [entry]
 
     found_start = False
 

pythonbuild/utils.py

@@ -159,21 +159,34 @@ def compress_python_archive(source_path: pathlib.Path,
     return dest_path
 
 
-def add_license_to_link_entry(entry):
-    """Add licenses keys to a ``link`` entry for JSON distribution info."""
-    name = entry['name']
+def add_licenses_to_extension_entry(entry):
+    """Add licenses keys to a ``extensions`` entry for JSON distribution info."""
 
-    for value in DOWNLOADS.values():
-        if name not in value.get('library_names', []):
-            continue
+    have_licenses = False
+    licenses = set()
+    license_paths = set()
+    license_public_domain = None
 
-        # Don't add licenses annotations if they aren't defined. This leaves
-        # things as "unknown" to consumers.
-        if 'licenses' not in value:
-            continue
+    for link in entry['links']:
+        name = link['name']
 
-        entry['licenses'] = value['licenses']
-        entry['license_path'] = 'licenses/%s' % value['license_file']
-        entry['license_public_domain'] = value.get('license_public_domain', False)
+        for value in DOWNLOADS.values():
+            if name not in value.get('library_names', []):
+                continue
 
+            # Don't add licenses annotations if they aren't defined. This leaves
+            # things as "unknown" to consumers.
+            if 'licenses' not in value:
+                continue
+
+            have_licenses = True
+            licenses |= set(value['licenses'])
+            license_paths.add('licenses/%s' % value['license_file'])
+            license_public_domain = value.get('license_public_domain', False)
+
+    if not have_licenses:
         return
+
+    entry['licenses'] = sorted(licenses)
+    entry['license_paths'] = sorted(license_paths)
+    entry['license_public_domain'] = license_public_domain