Merge pull request github#16399 from hvitved/csharp/unique-get-location

C#: Make `Element.getLocation` (mostly) functional

Author: hvitved

csharp/ql/lib/semmle/code/csharp/ExprOrStmtParent.qll

@@ -51,8 +51,6 @@ class TopLevelExprParent extends Element, @top_level_expr_parent {
   final Expr getAChildExpr() { result = this.getChildExpr(_) }
 }
 
-private predicate hasNoSourceLocation(Element e) { not e.getALocation() instanceof SourceLocation }
-
 /** INTERNAL: Do not use. */
 Expr getExpressionBody(Callable c) {
   result = c.getAChildExpr() and
@@ -67,17 +65,46 @@ private ControlFlowElement getBody(Callable c) {
   result = getStatementBody(c)
 }
 
+pragma[nomagic]
+private SourceLocation getASourceLocation(Element e) {
+  result = e.getALocation().(SourceLocation) and
+  not exists(e.getALocation().(SourceLocation).getMappedLocation())
+  or
+  result = e.getALocation().(SourceLocation).getMappedLocation()
+}
+
+pragma[nomagic]
+private predicate hasNoSourceLocation(Element e) { not exists(getASourceLocation(e)) }
+
+pragma[nomagic]
+private Location getFirstSourceLocation(Element e) {
+  result =
+    min(Location l, string filepath, int startline, int startcolumn, int endline, int endcolumn |
+      l = getASourceLocation(e) and
+      l.hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn)
+    |
+      l order by filepath, startline, startcolumn, endline, endcolumn
+    )
+}
+
 cached
 private module Cached {
   cached
   Location bestLocation(Element e) {
-    result = e.getALocation().(SourceLocation) and
-    not exists(e.getALocation().(SourceLocation).getMappedLocation())
-    or
-    result = e.getALocation().(SourceLocation).getMappedLocation()
+    (
+      if e.(Modifiable).isPartial() or e instanceof Namespace
+      then result = getASourceLocation(e)
+      else result = getFirstSourceLocation(e)
+    )
     or
     hasNoSourceLocation(e) and
-    result = min(Location l | l = e.getALocation() | l order by l.getFile().toString())
+    result =
+      min(Location l, string filepath |
+        l = e.getALocation() and
+        l.hasLocationInfo(filepath, _, _, _, _)
+      |
+        l order by filepath
+      )
     or
     not exists(e.getALocation()) and
     result instanceof EmptyLocation

csharp/ql/lib/semmle/code/csharp/Location.qll

@@ -63,7 +63,7 @@ class EmptyLocation extends Location {
  */
 class SourceLocation extends Location, @location_default {
   /** Gets the location that takes into account `#line` directives, if any. */
-  Location getMappedLocation() {
+  SourceLocation getMappedLocation() {
     locations_mapped(this, result) and
     not exists(LineDirective l | l.getALocation() = this)
   }