Address review comments

Author: hvitved

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

@@ -240,7 +240,7 @@ private predicate typeEqualityLeft(AstNode n1, TypePath path1, AstNode n2, TypeP
     any(PrefixExpr pe |
       pe.getOperatorName() = "*" and
       pe.getExpr() = n1 and
-      path1 = TypePath::consInverse(TRefTypeParameter(), path2)
+      path1.isCons(TRefTypeParameter(), path2)
     )
 }
 
@@ -926,7 +926,7 @@ private Type inferRefExprType(Expr e, TypePath path) {
     e = re.getExpr() and
     exists(TypePath exprPath, TypePath refPath, Type exprType |
       result = inferType(re, exprPath) and
-      exprPath = TypePath::consInverse(TRefTypeParameter(), refPath) and
+      exprPath.isCons(TRefTypeParameter(), refPath) and
       exprType = inferType(e)
     |
       if exprType = TRefType()
@@ -940,8 +940,9 @@ private Type inferRefExprType(Expr e, TypePath path) {
 
 pragma[nomagic]
 private Type inferTryExprType(TryExpr te, TypePath path) {
-  exists(TypeParam tp |
-    result = inferType(te.getExpr(), TypePath::consInverse(TTypeParamTypeParameter(tp), path))
+  exists(TypeParam tp, TypePath path0 |
+    result = inferType(te.getExpr(), path0) and
+    path0.isCons(TTypeParamTypeParameter(tp), path)
   |
     tp = any(ResultEnum r).getGenericParamList().getGenericParam(0)
     or
@@ -1017,7 +1018,7 @@ private module Cached {
     pragma[nomagic]
     Type getTypeAt(TypePath path) {
       exists(TypePath path0 | result = inferType(this, path0) |
-        path0 = TypePath::consInverse(TRefTypeParameter(), path)
+        path0.isCons(TRefTypeParameter(), path)
         or
         not path0.isCons(TRefTypeParameter(), _) and
         not (path0.isEmpty() and result = TRefType()) and

shared/typeinference/codeql/typeinference/internal/TypeInference.qll

@@ -228,22 +228,26 @@ module Make1<LocationSig Location, InputSig1<Location> Input1> {
      * so there is no need to check the length of `result`.
      */
     bindingset[this, result]
-    TypePath appendInverse(TypePath suffix) {
-      if result.isEmpty()
-      then this.isEmpty() and suffix.isEmpty()
-      else
-        if this.isEmpty()
-        then suffix = result
-        else (
-          result = this and suffix.isEmpty()
-          or
-          result = this + "." + suffix
-        )
+    TypePath appendInverse(TypePath suffix) { suffix = result.stripPrefix(this) }
+
+    /** Gets the path obtained by removing `prefix` from this path. */
+    bindingset[this, prefix]
+    TypePath stripPrefix(TypePath prefix) {
+      if prefix.isEmpty()
+      then result = this
+      else (
+        this = prefix and
+        result.isEmpty()
+        or
+        this = prefix + "." + result
+      )
     }
 
     /** Holds if this path starts with `tp`, followed by `suffix`. */
     bindingset[this]
-    predicate isCons(TypeParameter tp, TypePath suffix) { this = TypePath::consInverse(tp, suffix) }
+    predicate isCons(TypeParameter tp, TypePath suffix) {
+      suffix = this.stripPrefix(TypePath::singleton(tp))
+    }
   }
 
   /** Provides predicates for constructing `TypePath`s. */
@@ -260,15 +264,6 @@ module Make1<LocationSig Location, InputSig1<Location> Input1> {
      */
     bindingset[suffix]
     TypePath cons(TypeParameter tp, TypePath suffix) { result = singleton(tp).append(suffix) }
-
-    /**
-     * Gets the type path obtained by appending the singleton type path `tp`
-     * onto `suffix`.
-     */
-    bindingset[result]
-    TypePath consInverse(TypeParameter tp, TypePath suffix) {
-      result = singleton(tp).appendInverse(suffix)
-    }
   }
 
   /**