vim-patch:8.0.0251: not easy to select Python 2 or 3 (#9173)

Problem: It is not so easy to write a script that works with both Python 2 and Python 3, even when the Python code works with both.
Solution: Add 'pyxversion', :pyx, etc. (Marc Weber, Ken Takata)

f42dd3c390

src/nvim/ex_cmds2.c

@@ -2809,6 +2809,126 @@ void ex_options(exarg_T *eap)
   cmd_source((char_u *)SYS_OPTWIN_FILE, NULL);
 }
 
+// Detect Python 3 or 2, and initialize 'pyxversion'.
+void init_pyxversion(void)
+{
+  if (p_pyx == 0) {
+    if (!eval_has_provider("python3")) {
+      p_pyx = 3;
+    } else if (!eval_has_provider("python")) {
+      p_pyx = 2;
+    }
+  }
+}
+
+// Does a file contain one of the following strings at the beginning of any
+// line?
+// "#!(any string)python2"  => returns 2
+// "#!(any string)python3"  => returns 3
+// "# requires python 2.x"  => returns 2
+// "# requires python 3.x"  => returns 3
+// otherwise return 0.
+static int requires_py_version(char_u *filename)
+{
+  FILE      *file;
+  int       requires_py_version = 0;
+  int       i, lines;
+
+  lines = (int)p_mls;
+  if (lines < 0) {
+    lines = 5;
+  }
+
+  file = mch_fopen((char *)filename, "r");
+  if (file != NULL) {
+    for (i = 0; i < lines; i++) {
+      if (vim_fgets(IObuff, IOSIZE, file)) {
+        break;
+      }
+      if (i == 0 && IObuff[0] == '#' && IObuff[1] == '!') {
+        // Check shebang.
+        if (strstr((char *)IObuff + 2, "python2") != NULL) {
+          requires_py_version = 2;
+          break;
+        }
+        if (strstr((char *)IObuff + 2, "python3") != NULL) {
+          requires_py_version = 3;
+          break;
+        }
+      }
+      IObuff[21] = '\0';
+      if (STRCMP("# requires python 2.x", IObuff) == 0) {
+        requires_py_version = 2;
+        break;
+      }
+      if (STRCMP("# requires python 3.x", IObuff) == 0) {
+        requires_py_version = 3;
+        break;
+      }
+    }
+    fclose(file);
+  }
+  return requires_py_version;
+}
+
+
+// Source a python file using the requested python version.
+static void source_pyx_file(exarg_T *eap, char_u *fname)
+{
+  exarg_T ex;
+  long int v = requires_py_version(fname);
+
+  init_pyxversion();
+  if (v == 0) {
+    // user didn't choose a preference, 'pyx' is used
+    v = p_pyx;
+  }
+
+  // now source, if required python version is not supported show
+  // unobtrusive message.
+  if (eap == NULL) {
+    memset(&ex, 0, sizeof(ex));
+  } else {
+    ex = *eap;
+  }
+  ex.arg = fname;
+  ex.cmd = (char_u *)(v == 2 ? "pyfile" : "pyfile3");
+
+  if (v == 2) {
+    ex_pyfile(&ex);
+  } else {
+    ex_py3file(&ex);
+  }
+}
+
+// ":pyxfile {fname}"
+void ex_pyxfile(exarg_T *eap)
+{
+  source_pyx_file(eap, eap->arg);
+}
+
+// ":pyx"
+void ex_pyx(exarg_T *eap)
+{
+  init_pyxversion();
+  if (p_pyx == 2) {
+    ex_python(eap);
+  } else {
+    ex_python3(eap);
+  }
+}
+
+// ":pyxdo"
+void ex_pyxdo(exarg_T *eap)
+{
+  init_pyxversion();
+  if (p_pyx == 2) {
+    ex_pydo(eap);
+  } else {
+    ex_pydo3(eap);
+  }
+}
+
 /// ":source {fname}"
 void ex_source(exarg_T *eap)
 {