C#: Reduce size of getAThrownException()

csharp/ql/src/semmle/code/csharp/controlflow/ControlFlowElement.qll

@@ -19,6 +19,11 @@ class ControlFlowElement extends ExprOrStmtParent, @control_flow_element {
   /** Gets the enclosing callable of this element, if any. */
   Callable getEnclosingCallable() { none() }
 
+  /** Gets the assembly that this element was compiled into. */
+  Assembly getAssembly() {
+    result = this.getEnclosingCallable().getDeclaringType().getALocation()
+  }
+
   /**
    * Gets a control flow node for this element. That is, a node in the
    * control flow graph that corresponds to this element.

csharp/ql/src/semmle/code/csharp/controlflow/internal/Completion.qll

@@ -185,14 +185,28 @@ private class Overflowable extends UnaryOperation {
   }
 }
 
+private class CoreLib extends Assembly {
+  CoreLib() { this = any(SystemExceptionClass c).getALocation() }
+}
+
+/**
+ * Holds if assembly `a` was definitely compiled with core library `core`.
+ */
+pragma[noinline]
+private predicate assemblyCompiledWithCoreLib(Assembly a, CoreLib core) {
+  a.getAnAttribute().getType().getBaseClass*().(SystemAttributeClass).getALocation() = core
+}
+
 /** A control flow element that is inside a `try` block. */
 private class TriedControlFlowElement extends ControlFlowElement {
-  TriedControlFlowElement() { this = any(TryStmt try).getATriedElement() }
+  TryStmt try;
+
+  TriedControlFlowElement() { this = try.getATriedElement() }
 
   /**
    * Gets an exception class that is potentially thrown by this element, if any.
    */
-  Class getAThrownException() {
+  private Class getAThrownException0() {
     this instanceof Overflowable and
     result instanceof SystemOverflowExceptionClass
     or
@@ -249,6 +263,40 @@ private class TriedControlFlowElement extends ControlFlowElement {
     this instanceof StringLiteral and
     result instanceof SystemOutOfMemoryExceptionClass
   }
+
+  private CoreLib getCoreLibFromACatchClause() {
+    exists(SpecificCatchClause scc | scc = try.getACatchClause() |
+      result = scc.getCaughtExceptionType().getBaseClass*().(SystemExceptionClass).getALocation()
+    )
+  }
+
+  private CoreLib getCoreLib() {
+    result = this.getCoreLibFromACatchClause()
+    or
+    not exists(this.getCoreLibFromACatchClause()) and
+    assemblyCompiledWithCoreLib(this.getAssembly(), result)
+  }
+
+  pragma[noinline]
+  private Class getAThrownExceptionFromPlausibleCoreLib(string name) {
+    result = this.getAThrownException0() and
+    name = result.getQualifiedName() and
+    (
+      not exists(this.getCoreLib())
+      or
+      this.getCoreLib() = result.getALocation()
+    )
+  }
+
+  Class getAThrownException() {
+    exists(string name | result = this.getAThrownExceptionFromPlausibleCoreLib(name) |
+      result = min(Class c |
+          c = this.getAThrownExceptionFromPlausibleCoreLib(name)
+        |
+          c order by c.getLocation().(Assembly).getFullName()
+        )
+    )
+  }
 }
 
 pragma[noinline]

csharp/ql/src/semmle/code/csharp/frameworks/System.qll

@@ -56,6 +56,11 @@ class SystemArrayClass extends SystemClass {
   SystemArrayClass() { this.hasName("Array") }
 }
 
+/** `System.Attribute` class. */
+class SystemAttributeClass extends SystemClass {
+  SystemAttributeClass() { this.hasName("Attribute") }
+}
+
 /** The `System.Boolean` structure. */
 class SystemBooleanStruct extends BoolType {
   /** Gets the `Parse(string)` method. */