Rust: Minor tweaks

Author: paldepind

rust/ql/lib/codeql/rust/internal/TypeInference.qll

@@ -2154,12 +2154,13 @@ private predicate methodCallHasImplCandidate(MethodCall mc, Impl impl) {
 
 private module BlanketImplementation {
   /**
-   * Holds if `impl` is a blanket implementation, that is, an implementation of a
-   * trait for a type parameter.
+   * Gets the type parameter for which `impl` is a blanket implementation, if
+   * any.
    */
   private TypeParamItemNode getBlanketImplementationTypeParam(Impl impl) {
     result = impl.(ImplItemNode).resolveSelfTy() and
     result = impl.getGenericParamList().getAGenericParam() and
+    // This impl block is not superseded by the expansion of an attribute macro.
     not exists(impl.getAttributeMacroExpansion())
   }
 
@@ -2173,8 +2174,17 @@ private module BlanketImplementation {
   }
 
   /**
-   * Holds if `impl1` and `impl2` are duplicates and `impl2` is more "canonical"
-   * than `impl1`.
+   * Holds if `impl1` and `impl2` are duplicates and `impl2` is strictly more
+   * "canonical" than `impl1`.
+   *
+   * Libraries can often occur several times in the database for different
+   * library versions. This causes the same blanket implementations to exist
+   * multiple times, and these add no useful information.
+   *
+   * We detect these duplicates based on some simple heuristics (same trait
+   * name, file name, etc.). For these duplicates we select the one with the
+   * greatest file name (which usually is also the one with the greatest library
+   * version in the path)
    */
   predicate duplicatedImpl(Impl impl1, Impl impl2) {
     exists(string fileName, string traitName, int arity, string tpName |
@@ -2185,23 +2195,10 @@ private module BlanketImplementation {
     )
   }
 
-  predicate hasNoDuplicates(Impl impl) {
+  predicate isCanonicalImpl(Impl impl) {
     not duplicatedImpl(impl, _) and isBlanketImplementation(impl)
   }
 
-  /**
-   * We currently consider blanket implementations to be in scope "globally",
-   * even though they actually need to be imported to be used. One downside of
-   * this is that the libraries included in the database can often occur several
-   * times for different library versions. This causes the same blanket
-   * implementations to exist multiple times, and these add no useful
-   * information.
-   *
-   * We detect these duplicates based on some files heuristic (same trait name,
-   * file name, etc.). For these duplicates we select the one with the greatest
-   * file name (which usually is also the one with the greatest library version
-   * in the path)
-   */
   Impl getCanonicalImpl(Impl impl) {
     result =
       max(Impl impl0, Location l |
@@ -2210,7 +2207,7 @@ private module BlanketImplementation {
         impl0 order by l.getFile().getAbsolutePath(), l.getStartLine()
       )
     or
-    hasNoDuplicates(impl) and result = impl
+    isCanonicalImpl(impl) and result = impl
   }
 
   predicate isCanonicalBlanketImplementation(Impl impl) { impl = getCanonicalImpl(impl) }
@@ -2223,11 +2220,10 @@ private module BlanketImplementation {
     t =
       min(Trait trait, int i |
         trait = getBlanketImplementationTypeParam(impl).resolveBound(i) and
-        // Exclude traits that are "trivial" in the sense that they are known to
-        // not narrow things down very much.
+        // Exclude traits that are known to not narrow things down very much.
         not trait.getName().getText() =
           [
-            "Sized", "Clone", "Fn", "FnOnce", "FnMut",
+            "Sized", "Clone",
             // The auto traits
             "Send", "Sync", "Unpin", "UnwindSafe", "RefUnwindSafe"
           ]
@@ -2257,7 +2253,7 @@ private module BlanketImplementation {
       f = impl.resolveTraitTy().getAssocItem(name)
     ) and
     // If the method is already available through one of the trait bounds on the
-    // type parameter (because they share a common trait ancestor) then ignore
+    // type parameter (because they share a common ancestor trait) then ignore
     // it.
     not getBlanketImplementationTypeParam(impl).resolveABound().(TraitItemNode).getASuccessor(name) =
       f