[Python-checkins] gh-94772: Fix off-by-one error in Windows launcher (GH-94779)

[zooba]

https://github.com/python/cpython/commit/407ff6556cc999d692b264466ad8d32304a09bce
commit: 407ff6556cc999d692b264466ad8d32304a09bce
branch: main
author: Paul Moore <p.f.moore at gmail.com>
committer: zooba <steve.dower at microsoft.com>
date: 2022-07-16T10:02:22+01:00
summary:

gh-94772: Fix off-by-one error in Windows launcher (GH-94779)

files:
A Misc/NEWS.d/next/Windows/2022-07-12-20-45-43.gh-issue-94772.uNMmdG.rst
M Lib/test/test_launcher.py
M PC/launcher2.c

diff --git a/Lib/test/test_launcher.py b/Lib/test/test_launcher.py
index cd7b944f98f58..50a2e8c03d647 100644
--- a/Lib/test/test_launcher.py
+++ b/Lib/test/test_launcher.py
@@ -515,6 +515,30 @@ def test_py3_shebang(self):
         self.assertEqual("3.100-arm64", data["SearchInfo.tag"])
         self.assertEqual(f"X.Y-arm64.exe -X fake_arg_for_test -prearg {script} -postarg", data["stdout"].strip())
 
+    def test_py_shebang_nl(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python -prearg\n") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y.exe -prearg {script} -postarg", data["stdout"].strip())
+
+    def test_py2_shebang_nl(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python2 -prearg\n") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-32", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y-32.exe -prearg {script} -postarg", data["stdout"].strip())
+
+    def test_py3_shebang_nl(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python3 -prearg\n") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-arm64", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y-arm64.exe -X fake_arg_for_test -prearg {script} -postarg", data["stdout"].strip())
+
     def test_install(self):
         data = self.run_py(["-V:3.10"], env={"PYLAUNCHER_ALWAYS_INSTALL": "1"}, expect_returncode=111)
         cmd = data["stdout"].strip()
diff --git a/Misc/NEWS.d/next/Windows/2022-07-12-20-45-43.gh-issue-94772.uNMmdG.rst b/Misc/NEWS.d/next/Windows/2022-07-12-20-45-43.gh-issue-94772.uNMmdG.rst
new file mode 100644
index 0000000000000..bb5ab754484eb
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2022-07-12-20-45-43.gh-issue-94772.uNMmdG.rst
@@ -0,0 +1 @@
+Fix incorrect handling of shebang lines in py.exe launcher
diff --git a/PC/launcher2.c b/PC/launcher2.c
index ae11f4f024a90..c8ed1b0f7c8a6 100644
--- a/PC/launcher2.c
+++ b/PC/launcher2.c
@@ -874,7 +874,9 @@ checkShebang(SearchInfo *search)
     while (--bytesRead > 0 && *++b != '\r' && *b != '\n') { }
     wchar_t *shebang;
     int shebangLength;
-    int exitCode = _decodeShebang(search, start, (int)(b - start + 1), onlyUtf8, &shebang, &shebangLength);
+    // We add 1 when bytesRead==0, as in that case we hit EOF and b points
+    // to the last character in the file, not the newline
+    int exitCode = _decodeShebang(search, start, (int)(b - start + (bytesRead == 0)), onlyUtf8, &shebang, &shebangLength);
     if (exitCode) {
         return exitCode;
     }