1 files changed, 101 insertions, 0 deletions
diff --git a/pyproject_requirements_txt.py b/pyproject_requirements_txt.py
new file mode 100644
index 0000000..5ff1f26
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+++ b/pyproject_requirements_txt.py
@@ -0,0 +1,101 @@
+"""Best-effort parser for requirements.txt files"""
+
+import urllib.parse
+from pathlib import Path
+import sys
+import os
+import re
+
+# `#` starts a comment only at end of line and after whitespace
+COMMENT_RE = re.compile(r'(^|\s+)#.*$')
+
+# Assume URLs start with a scheme; don't look for "egg=" URLs otherwise
+URL_START_RE = re.compile(r'^[-_+a-zA-Z0-9]+://')
+
+ENV_VAR_RE = re.compile(r'(?P<var>\$\{(?P<name>[A-Z0-9_]+)\})')
+PKGNAME_RE = re.compile(r'^[-_a-zA-Z0-9]+')
+
+# The requirements.txt format evolved rather organically; expect weirdness.
+
+def convert_requirements_txt(lines, path:Path = None):
+    """Convert lines of a requirements file to PEP 440-style requirement strs
+
+    This does NOT handle all of requirements.txt features (only pip can do
+    that), but tries its best.
+
+    The resulting requirements might not actually be valid (either because
+    they're wrong in the file, or because we missed a special case).
+
+    path is the path to the requirements.txt file, used for options like `-r`.
+    """
+    requirements = []
+    lines = combine_logical_lines(lines)
+    lines = strip_comments(lines)
+    lines = expand_env_vars(lines)
+    if path:
+        filename = path.name
+    else:
+        filename = '<requirements file>'
+    for line in lines:
+        if URL_START_RE.match(line):
+            # Handle URLs with "egg=..." fragments
+            # see https://pip.pypa.io/en/stable/cli/pip_install/#vcs-support
+            parsed_url = urllib.parse.urlparse(line)
+            parsed_fragment = urllib.parse.parse_qs(parsed_url.fragment)
+            if 'egg' in parsed_fragment:
+                # Prepend the package name to the URL.
+                match = PKGNAME_RE.match(parsed_fragment['egg'][0])
+                if match:
+                    pkg_name = match[0]
+                    requirements.append(f'{pkg_name}@{line}')
+                    continue
+            # If that didn't work, pass the line on;
+            # the caller will deal with invalid requirements
+            requirements.append(line)
+        elif line.startswith('-r'):
+            recursed_path = line[2:].strip()
+            if path:
+                recursed_path = path.parent / recursed_path
+            recursed_path = Path(recursed_path)
+            with recursed_path.open() as f:
+                requirements.extend(convert_requirements_txt(f, recursed_path))
+        elif line.startswith('-'):
+            raise ValueError(f'{filename}: unsupported requirements file option: {line}')
+        else:
+            requirements.append(line)
+    return requirements
+
+def combine_logical_lines(lines):
+    """Combine logical lines together (backslash line-continuation)"""
+    pieces = []
+    for line in lines:
+        line = line.rstrip('\n')
+        # Whole-line comments *only* are removed before line-contionuation
+        if COMMENT_RE.match(line):
+            continue
+        if line.endswith('\\'):
+            pieces.append(line[:-1])
+        else:
+            # trailing whitespace is only removed from full logical lines
+            pieces.append(line.rstrip())
+            yield ''.join(pieces)
+            pieces = []
+    yield ''.join(pieces)
+
+
+def strip_comments(lines):
+    for line in lines:
+        line, *rest = COMMENT_RE.split(line, maxsplit=1)
+        line = line.strip()
+        if line:
+            yield line
+
+
+def expand_env_vars(lines):
+    def repl(match):
+        value = os.getenv(match['name'])
+        if value is None:
+            return match['var']
+        return value
+    for line in lines:
+        yield ENV_VAR_RE.sub(repl, line)