cmd/compile/internal/syntax, types2: move cmpPos to pos.Cmp

Make position comparison generally available.

Change-Id: I94b6f658fa19a15b30574dbb2181879115c131a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/307215
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/syntax/pos.go

@@ -59,6 +59,45 @@ func (pos Pos) RelCol() uint {
 	return pos.Col()
 }
 
+// Cmp compares the positions p and q and returns a result r as follows:
+//
+//	r <  0: p is before q
+//	r == 0: p and q are the same position (but may not be identical)
+//	r >  0: p is after q
+//
+// If p and q are in different files, p is before q if the filename
+// of p sorts lexicographically before the filename of q.
+func (p Pos) Cmp(q Pos) int {
+	pname := p.RelFilename()
+	qname := q.RelFilename()
+	switch {
+	case pname < qname:
+		return -1
+	case pname > qname:
+		return +1
+	}
+
+	pline := p.Line()
+	qline := q.Line()
+	switch {
+	case pline < qline:
+		return -1
+	case pline > qline:
+		return +1
+	}
+
+	pcol := p.Col()
+	qcol := q.Col()
+	switch {
+	case pcol < qcol:
+		return -1
+	case pcol > qcol:
+		return +1
+	}
+
+	return 0
+}
+
 func (pos Pos) String() string {
 	rel := position_{pos.RelFilename(), pos.RelLine(), pos.RelCol()}
 	abs := position_{pos.Base().Pos().RelFilename(), pos.Line(), pos.Col()}

src/cmd/compile/internal/syntax/testing.go

@@ -33,10 +33,10 @@ var errRx = regexp.MustCompile(`^ *ERROR *"?([^"]*)"?`)
 // for each Error is the position of the token immediately preceding
 // the comment, the Error message is the message msg extracted from
 // the comment, with all errors that are on the same line collected
-// in a slice. If there is no preceding token (the `ERROR` comment
-// appears in the beginning of the file), then the recorded position
-// is unknown (line, col = 0, 0). If there are no ERROR comments, the
-// result is nil.
+// in a slice, in source order. If there is no preceding token (the
+// `ERROR` comment appears in the beginning of the file), then the
+// recorded position is unknown (line, col = 0, 0). If there are no
+// ERROR comments, the result is nil.
 func ErrorMap(src io.Reader) (errmap map[uint][]Error) {
 	// position of previous token
 	var base *PosBase

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

@@ -383,45 +383,12 @@ func (check *Checker) cycleError(cycle []Object) {
 	check.report(&err)
 }
 
-// TODO(gri) This functionality should probably be with the Pos implementation.
-func cmpPos(p, q syntax.Pos) int {
-	// TODO(gri) is RelFilename correct here?
-	pname := p.RelFilename()
-	qname := q.RelFilename()
-	switch {
-	case pname < qname:
-		return -1
-	case pname > qname:
-		return +1
-	}
-
-	pline := p.Line()
-	qline := q.Line()
-	switch {
-	case pline < qline:
-		return -1
-	case pline > qline:
-		return +1
-	}
-
-	pcol := p.Col()
-	qcol := q.Col()
-	switch {
-	case pcol < qcol:
-		return -1
-	case pcol > qcol:
-		return +1
-	}
-
-	return 0
-}
-
 // firstInSrc reports the index of the object with the "smallest"
 // source position in path. path must not be empty.
 func firstInSrc(path []Object) int {
 	fst, pos := 0, path[0].Pos()
 	for i, t := range path[1:] {
-		if cmpPos(t.Pos(), pos) < 0 {
+		if t.Pos().Cmp(pos) < 0 {
 			fst, pos = i+1, t.Pos()
 		}
 	}

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

@@ -81,7 +81,7 @@ func (s *Scope) Lookup(name string) Object {
 // whose scope is the scope of the package that exported them.
 func (s *Scope) LookupParent(name string, pos syntax.Pos) (*Scope, Object) {
 	for ; s != nil; s = s.parent {
-		if obj := s.elems[name]; obj != nil && (!pos.IsKnown() || cmpPos(obj.scopePos(), pos) <= 0) {
+		if obj := s.elems[name]; obj != nil && (!pos.IsKnown() || obj.scopePos().Cmp(pos) <= 0) {
 			return s, obj
 		}
 	}
@@ -153,7 +153,7 @@ func (s *Scope) End() syntax.Pos { return s.end }
 // The result is guaranteed to be valid only if the type-checked
 // AST has complete position information.
 func (s *Scope) Contains(pos syntax.Pos) bool {
-	return cmpPos(s.pos, pos) <= 0 && cmpPos(pos, s.end) < 0
+	return s.pos.Cmp(pos) <= 0 && pos.Cmp(s.end) < 0
 }
 
 // Innermost returns the innermost (child) scope containing

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

@@ -66,7 +66,7 @@ func (check *Checker) usage(scope *Scope) {
 		}
 	}
 	sort.Slice(unused, func(i, j int) bool {
-		return cmpPos(unused[i].pos, unused[j].pos) < 0
+		return unused[i].pos.Cmp(unused[j].pos) < 0
 	})
 	for _, v := range unused {
 		check.softErrorf(v.pos, "%s declared but not used", v.name)