python/shebang: fix broken shebangs like #!python

Signed-off-by: botantony <[email protected]>

Author: botantony

Library/Homebrew/language/python.rb

@@ -112,7 +112,7 @@ module Shebang
       module_function
 
       # A regex to match potential shebang permutations.
-      PYTHON_SHEBANG_REGEX = %r{^#! ?/usr/bin/(?:env )?python(?:[23](?:\.\d{1,2})?)?( |$)}
+      PYTHON_SHEBANG_REGEX = %r{^#! ?(?:/usr/bin/(?:env )?)?python(?:[23](?:\.\d{1,2})?)?( |$)}
 
       # The length of the longest shebang matching `SHEBANG_REGEX`.
       PYTHON_SHEBANG_MAX_LENGTH = T.let("#! /usr/bin/env pythonx.yyy ".length, Integer)

Library/Homebrew/test/language/python/shebang_spec.rb

@@ -5,6 +5,7 @@
 
 RSpec.describe Language::Python::Shebang do
   let(:file) { Tempfile.new("python-shebang") }
+  let(:broken_file) { Tempfile.new("python-shebang") }
   let(:f) do
     f = {}
 
@@ -40,9 +41,17 @@
       c
     EOS
     file.flush
+
+    broken_file.write <<~EOS
+      #!python
+      a
+      b
+      c
+    EOS
+    broken_file.flush
   end
 
-  after { file.unlink }
+  after { [file, broken_file].each(&:unlink) }
 
   describe "#detected_python_shebang" do
     it "can be used to replace Python shebangs" do
@@ -72,6 +81,20 @@
       EOS
     end
 
+    it "can replace `#!python` shebang" do
+      Utils::Shebang.rewrite_shebang(
+        described_class.detected_python_shebang(f[:versioned_python_dep],
+                                                use_python_from_path: true), broken_file.path
+      )
+
+      expect(File.read(broken_file)).to eq <<~EOS
+        #!/usr/bin/env python3
+        a
+        b
+        c
+      EOS
+    end
+
     it "errors if formula doesn't depend on python" do
       expect do
         Utils::Shebang.rewrite_shebang(