Python: Fix import root computation for windows and 3.7

Author: markshannon

python/ql/src/semmle/python/Files.qll

@@ -339,9 +339,21 @@ abstract class Container extends @container {
 
     /** Holds if this folder is the root folder for the standard library. */
     predicate isStdLibRoot(int major, int minor) {
-        allowable_version(major, minor) and
-        this.isImportRoot() and
-        this.getBaseName().regexpMatch("python" + major + "." + minor)
+        major = major_version() and minor = minor_version() and
+        this.isStdLibRoot()
+    }
+
+    /** Holds if this folder is the root folder for the standard library. */
+    predicate isStdLibRoot() {
+        /* Look for a standard lib module and find its import path
+         * We use `os` as it is the most likely to be imported and
+         * `tty` because it is small for testing.
+         */
+        exists(Module m |
+            m.getName() = "os" or m.getName() = "tty"
+            |
+            m.getFile().getImportRoot() = this
+        )
     }
 
     /** Gets the path element from which this container would be loaded. */
@@ -375,12 +387,6 @@ private string get_path(string name) {
     py_flags_versioned(name, result, _)
 }
 
-private predicate allowable_version(int major, int minor) {
-    major = 2 and minor in [6..7]
-    or
-    major = 3 and minor in [3..6]
-}
-
 class Location extends @location {
 
     /** Gets the file for this location */

python/ql/src/semmle/python/Module.qll

@@ -158,7 +158,7 @@ class Module extends Module_, Scope, AstNode {
 
     /** Holds if this module is in the standard library */
     predicate inStdLib() {
-        this.inStdLib(_, _)
+        this.getLoadPath().isStdLibRoot()
     }
 
     override

python/ql/src/semmle/python/dependencies/TechInventory.qll

@@ -50,7 +50,7 @@ class DistPackage extends ExternalPackage {
             parent = this.(ModuleObject).getPath().getParent() and
             parent.isImportRoot() and
             /* Not in standard library */
-            not parent.isStdLibRoot(_, _) and
+            not parent.isStdLibRoot() and
             /* Not in the source */
             not exists(parent.getRelativePath())
         )