cmd/compile/internal/types2: enable TestSelection API test

This test was never fully ported from go/types. Implement
a conversion function from syntax.Pos to string index so
that the test can be enabled again.

Also renamed the local variable syntax to segment to avoid
confusion with the syntax package.

Change-Id: I1b34e50ec138403798efb14c828545780f565507
Reviewed-on: https://go-review.googlesource.com/c/go/+/344253
Trust: Robert Griesemer <[email protected]>
Trust: Dan Scales <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>
Reviewed-by: Dan Scales <[email protected]>

Author: griesemer

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

@@ -17,10 +17,6 @@ import (
 	. "cmd/compile/internal/types2"
 )
 
-func unimplemented() {
-	panic("unimplemented")
-}
-
 // genericPkg is a source prefix for packages that contain generic code.
 const genericPkg = "package generic_"
 
@@ -1168,8 +1164,6 @@ func (m testImporter) Import(path string) (*Package, error) {
 }
 
 func TestSelection(t *testing.T) {
-	t.Skip("requires fixes around source positions")
-
 	selections := make(map[*syntax.SelectorExpr]*Selection)
 
 	imports := make(testImporter)
@@ -1293,11 +1287,9 @@ func main() {
 	for e, sel := range selections {
 		_ = sel.String() // assertion: must not panic
 
-		unimplemented()
-		_ = e
-		// start := fset.Position(e.Pos()).Offset
-		// end := fset.Position(e.End()).Offset
-		// syntax := mainSrc[start:end] // (all SelectorExprs are in main, not lib)
+		start := indexFor(mainSrc, syntax.StartPos(e))
+		end := indexFor(mainSrc, syntax.EndPos(e))
+		segment := mainSrc[start:end] // (all SelectorExprs are in main, not lib)
 
 		direct := "."
 		if sel.Indirect() {
@@ -1307,13 +1299,11 @@ func main() {
 			sel.String(),
 			fmt.Sprintf("%s%v", direct, sel.Index()),
 		}
-		unimplemented()
-		_ = got
-		// want := wantOut[syntax]
-		// if want != got {
-		// 	t.Errorf("%s: got %q; want %q", syntax, got, want)
-		// }
-		// delete(wantOut, syntax)
+		want := wantOut[segment]
+		if want != got {
+			t.Errorf("%s: got %q; want %q", segment, got, want)
+		}
+		delete(wantOut, segment)
 
 		// We must explicitly assert properties of the
 		// Signature's receiver since it doesn't participate
@@ -1323,17 +1313,29 @@ func main() {
 			got := sig.Recv().Type()
 			want := sel.Recv()
 			if !Identical(got, want) {
-				unimplemented()
-				// t.Errorf("%s: Recv() = %s, want %s", syntax, got, want)
+				t.Errorf("%s: Recv() = %s, want %s", segment, got, want)
 			}
 		} else if sig != nil && sig.Recv() != nil {
 			t.Errorf("%s: signature has receiver %s", sig, sig.Recv().Type())
 		}
 	}
 	// Assert that all wantOut entries were used exactly once.
-	for syntax := range wantOut {
-		t.Errorf("no syntax.Selection found with syntax %q", syntax)
+	for segment := range wantOut {
+		t.Errorf("no syntax.Selection found with syntax %q", segment)
+	}
+}
+
+// indexFor returns the index into s corresponding to the position pos.
+func indexFor(s string, pos syntax.Pos) int {
+	i, line := 0, 1 // string index and corresponding line
+	target := int(pos.Line())
+	for line < target && i < len(s) {
+		if s[i] == '\n' {
+			line++
+		}
+		i++
 	}
+	return i + int(pos.Col()-1) // columns are 1-based
 }
 
 func TestIssue8518(t *testing.T) {