Fix code review findings in 'line' directives

csharp/ql/src/semmle/code/csharp/Preprocessor.qll

@@ -163,7 +163,7 @@ class LineDirective extends PreprocessorDirective, @directive_line {
   /** Gets the succeeding `#line` directive in the file, if any. */
   LineDirective getSuccLineDirective() {
     result =
-      rank[1](LineDirective next |
+      min(LineDirective next |
         next.getFile() = this.getFile() and
         next.getLocation().getStartLine() > this.getLocation().getStartLine()
       |
@@ -216,10 +216,10 @@ class NumericLineDirective extends LineDirective {
   int getLine() { directive_line_values(this, result, _) }
 
   /** Holds if this directive specifies a file name. */
-  predicate hasFileName() { this.getFileName() != "" }
+  predicate hasFileName() { exists(this.getFileName()) }
 
-  /** Gets the file name of this directive. */
-  string getFileName() { directive_line_values(this, _, result) }
+  /** Gets the file name of this directive, if any. */
+  string getFileName() { directive_line_values(this, _, result) and result != "" }
 
   override string getAPrimaryQlClass() { result = "NumericLineDirective" }
 }

csharp/ql/test/library-tests/comments/LineDirectives.expected

@@ -4,7 +4,7 @@ hidden
 | trivia.cs:25:1:25:38 | #line hidden |
 lines
 | trivia.cs:18:1:18:19 | #line ... | 200 | Special |
-| trivia.cs:27:1:27:9 | #line ... | 300 |  |
+| trivia.cs:27:1:27:9 | #line ... | 300 | no file |
 succ
 | trivia.cs:18:1:18:19 | #line ... | trivia.cs:21:1:21:13 | #line default |
 | trivia.cs:21:1:21:13 | #line default | trivia.cs:25:1:25:38 | #line hidden |

csharp/ql/test/library-tests/comments/LineDirectives.ql

@@ -5,7 +5,8 @@ query predicate default(DefaultLineDirective line) { any() }
 query predicate hidden(HiddenLineDirective line) { any() }
 
 query predicate lines(NumericLineDirective line, int l, string file) {
-  line.getLine() = l and line.getFileName() = file
+  line.getLine() = l and
+  if line.hasFileName() then line.getFileName() = file else file = "no file"
 }
 
 query predicate succ(LineDirective d, LineDirective succ) { d.getSuccLineDirective() = succ }