gh-37018: `sage --package properties`
    
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For example:
```
$ ./sage -package properties --format shell gap ecl
git:sage_package_properties
path_ecl='/Users/mkoeppe/s/sage/sage-rebasing/worktree-
pristine/build/pkgs/ecl'
version_with_patchlevel_ecl='21.2.1'
type_ecl='standard'
source_ecl='normal'
trees_ecl='SAGE_LOCAL'
path_gap='/Users/mkoeppe/s/sage/sage-rebasing/worktree-
pristine/build/pkgs/gap'
version_with_patchlevel_gap='4.12.2'
type_gap='standard'
source_gap='normal'
trees_gap='SAGE_LOCAL'
```
The output is suitable as input for `eval` in Bourne shell. (The default
output format is more human-friendly.)

<!-- Why is this change required? What problem does it solve? -->
Split out from:
- #36740

where this new interface is used to eliminate direct references to
`build/pkgs/` from various scripts and reduce code duplication and
complexity in reading SPKG metadata.

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example "Fixes #12345". -->
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### ⌛ Dependencies

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URL: #37018
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

Author: Release Manager

build/sage_bootstrap/app.py

@@ -77,6 +77,37 @@ def list_cls(self, *package_classes, **filters):
         for pkg_name in pc.names:
             print(pkg_name)
 
+    def properties(self, *package_classes, **kwds):
+        """
+        Show the properties of given packages
+
+        $ sage --package properties --format shell maxima
+        path_maxima='........./build/pkgs/maxima'
+        version_with_patchlevel_maxima='5.46.0'
+        type_maxima='standard'
+        source_maxima='normal'
+        trees_maxima='SAGE_LOCAL'
+        """
+        props = kwds.pop('props', ['path', 'version_with_patchlevel', 'type', 'source', 'trees'])
+        format = kwds.pop('format', 'plain')
+        log.debug('Looking up properties')
+        pc = PackageClass(*package_classes)
+        for package_name in pc.names:
+            package = Package(package_name)
+            if format == 'plain':
+                print("{0}:".format(package_name))
+            for p in props:
+                value = getattr(package, p)
+                if value is None:
+                    if p.startswith('version'):
+                        value = 'none'
+                    else:
+                        value = ''
+                if format == 'plain':
+                    print("        {0:28} {1}".format(p + ":", value))
+                else:
+                    print("{0}_{1}='{2}'".format(p, package_name, value))
+
     def name(self, tarball_filename):
         """
         Find the package name given a tarball filename

build/sage_bootstrap/cmdline.py

@@ -83,6 +83,22 @@
 """
 
 
+epilog_properties = \
+"""
+Print properties of given package.
+
+EXAMPLE:
+
+    $ sage --package properties maxima
+    maxima:
+            path:                        /.../build/pkgs/maxima
+            version_with_patchlevel:     5.46.0
+            type:                        standard
+            source:                      normal
+            trees:                       SAGE_LOCAL
+"""
+
+
 epilog_name = \
 """
 Find the package name given a tarball filename
@@ -257,6 +273,19 @@ def make_parser():
         '--exclude-dependencies', action='store_true',
         help='exclude (ordinary) dependencies of the packages recursively')
 
+    parser_properties = subparsers.add_parser(
+        'properties', epilog=epilog_properties,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+        help='Print properties of given packages')
+    parser_properties.add_argument(
+        'package_class', metavar='[package_name|:package_type:]',
+        type=str, nargs='+',
+        help=('package name or designator for all packages of a given type '
+              '(one of :all:, :standard:, :optional:, and :experimental:)'))
+    parser_properties.add_argument(
+        '--format', type=str, default='plain',
+        help='output format (one of plain and shell; default: plain)')
+
     parser_name = subparsers.add_parser(
         'name', epilog=epilog_name,
         formatter_class=argparse.RawDescriptionHelpFormatter,
@@ -404,6 +433,8 @@ def run():
                      exclude=args.exclude,
                      include_dependencies=args.include_dependencies,
                      exclude_dependencies=args.exclude_dependencies)
+    elif args.subcommand == 'properties':
+        app.properties(*args.package_class, format=args.format)
     elif args.subcommand == 'name':
         app.name(args.tarball_filename)
     elif args.subcommand == 'tarball':

build/sage_bootstrap/package.py

@@ -48,6 +48,7 @@ def __init__(self, package_name):
         self._init_type()
         self._init_install_requires()
         self._init_dependencies()
+        self._init_trees()
 
     def __repr__(self):
         return 'Package {0}'.format(self.name)
@@ -293,13 +294,62 @@ def patchlevel(self):
         """
         return self.__patchlevel
 
+    @property
+    def version_with_patchlevel(self):
+        """
+        Return the version, including the Sage-specific patchlevel
+
+        OUTPUT:
+
+        String.
+        """
+        v = self.version
+        if v is None:
+            return v
+        p = self.patchlevel
+        if p < 0:
+            return v
+        return "{0}.p{1}".format(v, p)
+
     @property
     def type(self):
         """
         Return the package type
         """
         return self.__type
 
+    @property
+    def source(self):
+        """
+        Return the package source type
+        """
+        if self.has_file('requirements.txt'):
+            return 'pip'
+        if self.tarball_filename:
+            if self.tarball_filename.endswith('.whl'):
+                return 'wheel'
+            return 'normal'
+        if self.has_file('spkg-install') or self.has_file('spkg-install.in'):
+            return 'script'
+        return 'none'
+
+    @property
+    def trees(self):
+        """
+        Return the installation trees for the package
+
+        OUTPUT:
+
+        A white-space-separated string of environment variable names
+        """
+        if self.__trees is not None:
+            return self.__trees
+        if self.__install_requires is not None:
+            return 'SAGE_VENV'
+        if self.has_file('requirements.txt'):
+            return 'SAGE_VENV'
+        return 'SAGE_LOCAL'
+
     @property
     def distribution_name(self):
         """
@@ -466,3 +516,10 @@ def _init_dependencies(self):
                 self.__dependencies_order_only = f.readline()
         except IOError:
             self.__dependencies_order_only = ''
+
+    def _init_trees(self):
+        try:
+            with open(os.path.join(self.path, 'trees.txt')) as f:
+                self.__trees = f.readline().partition('#')[0].strip()
+        except IOError:
+            self.__trees = None