Rust: Fix bad join

Author: paldepind

rust/ql/lib/codeql/rust/elements/internal/FunctionImpl.qll

@@ -4,6 +4,7 @@
  * INTERNAL: Do not use.
  */
 
+private import codeql.files.FileSystem
 private import codeql.rust.elements.internal.generated.Function
 private import codeql.rust.elements.Comment
 
@@ -28,6 +29,30 @@ module Impl {
   class Function extends Generated::Function {
     override string toStringImpl() { result = "fn " + this.getName().getText() }
 
+    pragma[nomagic]
+    private predicate hasPotentialCommentAt(File f, int line) {
+      f = this.getLocation().getFile() and
+      // When a function is preceded by comments its start line is the line of
+      // the first comment. Hence all relevant comments are found by including
+      // comments from the start line and up to the line with the function
+      // name.
+      line in [this.getLocation().getStartLine() .. this.getName().getLocation().getStartLine()]
+    }
+
+    /**
+     * Gets a comment preceding this function.
+     *
+     * A comment is considered preceding if it occurs immediately before this
+     * function or if only other comments occur between the comment and this
+     * function.
+     */
+    Comment getAPrecedingComment() {
+      exists(File f, int line |
+        this.hasPotentialCommentAt(f, line) and
+        result.getLocation().hasLocationFileInfo(f, line, _, _, _)
+      )
+    }
+
     /**
      * Gets a comment preceding this function.
      *

rust/ql/lib/utils/test/InlineMadTest.qll

@@ -5,7 +5,7 @@ private module InlineMadTestLang implements InlineMadTestLangSig {
   class Callable = R::Function;
 
   string getComment(R::Function callable) {
-    result = callable.getPrecedingComment().getCommentText()
+    result = callable.getAPrecedingComment().getCommentText()
   }
 }
 

rust/ql/test/library-tests/type-inference/type-inference.ql

@@ -11,9 +11,9 @@ module ResolveTest implements TestSig {
   string getARelevantTag() { result = ["method", "fieldof"] }
 
   private predicate functionHasValue(Function f, string value) {
-    f.getPrecedingComment().getCommentText() = value
+    f.getAPrecedingComment().getCommentText() = value
     or
-    not exists(f.getPrecedingComment()) and
+    not exists(f.getAPrecedingComment()) and
     value = f.getName().getText()
   }