go/types, types2: move tparamIndex from unify.go into infer.go

Minor code reorganization: the next version of unify.go doesn't
need this function anymore, so move it where it is still used.

Change-Id: I6744a2361b5dfe2564ec73787a7a110e85ac9f1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/463230
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Auto-Submit: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>

Author: griesemer

src/cmd/compile/internal/types2/infer.go

@@ -775,3 +775,18 @@ func (w *cycleFinder) varList(list []*Var) {
 		w.typ(v.typ)
 	}
 }
+
+// If tpar is a type parameter in list, tparamIndex returns the type parameter index.
+// Otherwise, the result is < 0. tpar must not be nil.
+func tparamIndex(list []*TypeParam, tpar *TypeParam) int {
+	// Once a type parameter is bound its index is >= 0. However, there are some
+	// code paths (namely tracing and type hashing) by which it is possible to
+	// arrive here with a type parameter that has not been bound, hence the check
+	// for 0 <= i below.
+	// TODO(rfindley): investigate a better approach for guarding against using
+	// unbound type parameters.
+	if i := tpar.index; 0 <= i && i < len(list) && list[i] == tpar {
+		return i
+	}
+	return -1
+}

src/cmd/compile/internal/types2/unify.go

@@ -156,21 +156,6 @@ func (u *unifier) index(typ Type) int {
 	return -1
 }
 
-// If tpar is a type parameter in list, tparamIndex returns the type parameter index.
-// Otherwise, the result is < 0. tpar must not be nil.
-func tparamIndex(list []*TypeParam, tpar *TypeParam) int {
-	// Once a type parameter is bound its index is >= 0. However, there are some
-	// code paths (namely tracing and type hashing) by which it is possible to
-	// arrive here with a type parameter that has not been bound, hence the check
-	// for 0 <= i below.
-	// TODO(rfindley): investigate a better approach for guarding against using
-	// unbound type parameters.
-	if i := tpar.index; 0 <= i && i < len(list) && list[i] == tpar {
-		return i
-	}
-	return -1
-}
-
 // setIndex sets the type slot index for the i'th type parameter
 // (and all its joined parameters) to tj. The type parameter
 // must have a (possibly nil) type slot associated with it.