go/analysis/passes/shift: support constants in float syntax

Adds support for integer constants expressed in float syntax '2.0'.
Also fixes the same issue in gopls/internal/golang/hover.go.

Fixes golang/go#65939

Change-Id: Ic42b4cc7c6aedf7f115e3195044f06001cb6fb12
Reviewed-on: https://go-review.googlesource.com/c/tools/+/567115
TryBot-Result: Gopher Robot <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Run-TryBot: Tim King <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: timothy-king

go/analysis/passes/shift/shift.go

@@ -89,7 +89,8 @@ func checkLongShift(pass *analysis.Pass, node ast.Node, x, y ast.Expr) {
 	if v == nil {
 		return
 	}
-	amt, ok := constant.Int64Val(v)
+	u := constant.ToInt(v) // either an Int or Unknown
+	amt, ok := constant.Int64Val(u)
 	if !ok {
 		return
 	}

go/analysis/passes/shift/testdata/src/a/a.go

@@ -153,3 +153,8 @@ func ShiftDeadCode() {
 		_ = i << 64 // want "too small for shift"
 	}
 }
+
+func issue65939() {
+	a := 1
+	println(a << 2.0)
+}

gopls/internal/golang/hover.go

@@ -873,7 +873,7 @@ func objectString(obj types.Object, qf types.Qualifier, declPos token.Pos, file
 		case *types.Named:
 			// Try to add a formatted duration as an inline comment.
 			pkg := typ.Obj().Pkg()
-			if pkg.Path() == "time" && typ.Obj().Name() == "Duration" {
+			if pkg.Path() == "time" && typ.Obj().Name() == "Duration" && obj.Val().Kind() == constant.Int {
 				if d, ok := constant.Int64Val(obj.Val()); ok {
 					comment = time.Duration(d).String()
 				}