Python: Move exception modelling to DataFlowDispatch.qll

This analysis will is needed for the reachability modelling (which
tracks things like which exceptions are caught by which handles), so it
makes more sense for it to move to `DataFlowDispatch` for now.

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -2114,3 +2114,113 @@ module DuckTyping {
     f.getADecorator().(Name).getId() = "property"
   }
 }
+
+/**
+ * Provides a class hierarchy for exception types, covering both builtin
+ * exceptions (from typeshed models) and user-defined exception classes.
+ */
+module ExceptionTypes {
+  private import semmle.python.ApiGraphs
+  private import semmle.python.frameworks.data.internal.ApiGraphModels
+
+  /** Holds if `name` is a builtin exception class name. */
+  predicate builtinException(string name) {
+    typeModel("builtins.BaseException~Subclass", "builtins." + name, "")
+  }
+
+  /** Holds if builtin exception `sub` is a direct subclass of builtin exception `base`. */
+  private predicate builtinExceptionSubclass(string base, string sub) {
+    typeModel("builtins." + base + "~Subclass", "builtins." + sub, "")
+  }
+
+  /** An exception type, either a builtin exception or a user-defined exception class. */
+  newtype TExceptType =
+    /** A user-defined exception class. */
+    TUserExceptType(Class c) or
+    /** A builtin exception class, identified by name. */
+    TBuiltinExceptType(string name) { builtinException(name) }
+
+  /** An exception type, either a builtin exception or a user-defined exception class. */
+  class ExceptType extends TExceptType {
+    /** Gets the name of this exception type. */
+    string getName() { none() }
+
+    /** Gets a data-flow node that refers to this exception type. */
+    DataFlow::Node getAUse() { none() }
+
+    /** Gets a direct superclass of this exception type. */
+    ExceptType getADirectSuperclass() { none() }
+
+    /** Gets a string representation of this exception type. */
+    string toString() { result = this.getName() }
+
+    /**
+     * Holds if this element is at the specified location.
+     * The location spans column `startColumn` of line `startLine` to
+     * column `endColumn` of line `endLine` in file `filepath`.
+     * For more information, see
+     * [Providing locations in CodeQL queries](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+     */
+    predicate hasLocationInfo(
+      string filePath, int startLine, int startColumn, int endLine, int endColumn
+    ) {
+      none()
+    }
+  }
+
+  /** A user-defined exception class. */
+  class UserExceptType extends ExceptType, TUserExceptType {
+    Class cls;
+
+    UserExceptType() { this = TUserExceptType(cls) }
+
+    /** Gets the underlying class. */
+    Class asClass() { result = cls }
+
+    override string getName() { result = cls.getName() }
+
+    override DataFlow::Node getAUse() { result = classTracker(cls) }
+
+    override ExceptType getADirectSuperclass() {
+      result.(UserExceptType).asClass() = getADirectSuperclass(cls)
+      or
+      result.(BuiltinExceptType).getAUse().asExpr() = cls.getABase()
+    }
+
+    override predicate hasLocationInfo(
+      string filePath, int startLine, int startColumn, int endLine, int endColumn
+    ) {
+      cls.getLocation().hasLocationInfo(filePath, startLine, startColumn, endLine, endColumn)
+    }
+  }
+
+  /** A builtin exception class, identified by name. */
+  class BuiltinExceptType extends ExceptType, TBuiltinExceptType {
+    string name;
+
+    BuiltinExceptType() { this = TBuiltinExceptType(name) }
+
+    /** Gets the builtin name. */
+    string asBuiltinName() { result = name }
+
+    override string getName() { result = name }
+
+    override DataFlow::Node getAUse() { API::builtin(name).asSource().flowsTo(result) }
+
+    override ExceptType getADirectSuperclass() {
+      builtinExceptionSubclass(result.(BuiltinExceptType).asBuiltinName(), name) and
+      result != this
+    }
+
+    override predicate hasLocationInfo(
+      string filePath, int startLine, int startColumn, int endLine, int endColumn
+    ) {
+      filePath = "" and
+      startLine = 0 and
+      startColumn = 0 and
+      endLine = 0 and
+      endColumn = 0
+    }
+  }
+}
+

python/ql/src/Exceptions/IncorrectExceptOrder.ql

@@ -15,74 +15,7 @@
 
 import python
 import semmle.python.dataflow.new.internal.DataFlowDispatch
-import semmle.python.ApiGraphs
-import semmle.python.frameworks.data.internal.ApiGraphModels
-
-predicate builtinException(string name) {
-  typeModel("builtins.BaseException~Subclass", "builtins." + name, "")
-}
-
-predicate builtinExceptionSubclass(string base, string sub) {
-  typeModel("builtins." + base + "~Subclass", "builtins." + sub, "")
-}
-
-newtype TExceptType =
-  TClass(Class c) or
-  TBuiltin(string name) { builtinException(name) }
-
-class ExceptType extends TExceptType {
-  Class asClass() { this = TClass(result) }
-
-  string asBuiltinName() { this = TBuiltin(result) }
-
-  predicate isBuiltin() { this = TBuiltin(_) }
-
-  string getName() {
-    result = this.asClass().getName()
-    or
-    result = this.asBuiltinName()
-  }
-
-  string toString() { result = this.getName() }
-
-  DataFlow::Node getAUse() {
-    result = classTracker(this.asClass())
-    or
-    API::builtin(this.asBuiltinName()).asSource().flowsTo(result)
-  }
-
-  ExceptType getADirectSuperclass() {
-    result.asClass() = getADirectSuperclass(this.asClass())
-    or
-    result.isBuiltin() and
-    result.getAUse().asExpr() = this.asClass().getABase()
-    or
-    builtinExceptionSubclass(result.asBuiltinName(), this.asBuiltinName()) and
-    this != result
-  }
-
-  /**
-   * Holds if this element is at the specified location.
-   * The location spans column `startColumn` of line `startLine` to
-   * column `endColumn` of line `endLine` in file `filepath`.
-   * For more information, see
-   * [Providing locations in CodeQL queries](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
-   */
-  predicate hasLocationInfo(
-    string filePath, int startLine, int startColumn, int endLine, int endColumn
-  ) {
-    this.asClass()
-        .getLocation()
-        .hasLocationInfo(filePath, startLine, startColumn, endLine, endColumn)
-    or
-    this.isBuiltin() and
-    filePath = "" and
-    startLine = 0 and
-    startColumn = 0 and
-    endLine = 0 and
-    endColumn = 0
-  }
-}
+private import ExceptionTypes
 
 predicate incorrectExceptOrder(ExceptStmt ex1, ExceptType cls1, ExceptStmt ex2, ExceptType cls2) {
   exists(int i, int j, Try t |