compiler: change 'declared and not used' to 'declared but not used'

Go v1.14 has changed this error message, so now that v1.14 is the
minimum Go version supported, change it also in Scriggo.

For #385

compiler/checker.go

@@ -289,7 +289,7 @@ func (tc *typechecker) exitScope() {
 			cut = i
 		}
 		if len(unused) > 0 {
-			panic(tc.errorf(unused[len(unused)-1].node, "%s declared and not used", unused[len(unused)-1].ident))
+			panic(tc.errorf(unused[len(unused)-1].node, "%s declared but not used", unused[len(unused)-1].ident))
 		}
 		tc.unusedVars = tc.unusedVars[:cut]
 	}

compiler/checker_statements.go

@@ -806,7 +806,7 @@ nodesLoop:
 					// Append the new nodes removing the function literal.
 					nodes = append(nodes[:i], append(newNodes, nodes[i+1:]...)...)
 					tc.scriptFuncDecl = backup
-					// Avoid error 'declared and not used' by "using" the
+					// Avoid error 'declared but not used' by "using" the
 					// identifier.
 					tc.checkIdentifier(ident, true)
 					i += 2

compiler/checker_test.go

@@ -640,7 +640,7 @@ const noNewVariables = "no new variables on left side of :="
 const cannotUseBlankAsValue = "cannot use _ as value"
 
 func declaredNotUsed(v string) string {
-	return v + " declared and not used"
+	return v + " declared but not used"
 }
 
 func redeclaredInThisBlock(v string) string {
@@ -1308,7 +1308,7 @@ var checkerStmts = map[string]string{
 	// `nil.F()`:     `use of untyped nil`, // TODO: panics.
 	`_()`: `cannot use _ as value`,
 
-	// Variable declared and not used.
+	// Variable declared but not used.
 	`a := 0; { _ = a }`:          ok,
 	`{ { a := 0 } }`:             declaredNotUsed("a"),
 	`{ const A = 0; var B = 0 }`: declaredNotUsed("B"),

test/compare/run_test.go

@@ -32,7 +32,7 @@ func Test_errorcheck(t *testing.T) {
 			src: joinLines([]string{
 				`package main`,
 				`func main() {`,
-				`	x := 3 // ERROR "x declared and not used"`,
+				`	x := 3 // ERROR "x declared but not used"`,
 				`}`,
 			}),
 			ext: ".go",

test/compare/testdata/errors/bad_for.go

@@ -3,5 +3,5 @@
 package main
 
 func main() {
-	for i := range []int{} { } // ERROR "i declared and not used"
+	for i := range []int{} { } // ERROR "i declared but not used"
 }

test/compare/testdata/github.com-golang-go/fixedbugs/bug373.go

@@ -1,4 +1,4 @@
-// skip : 'declared and not used' not reported in type switch https://github.com/open2b/scriggo/issues/474
+// skip : 'declared but not used' not reported in type switch https://github.com/open2b/scriggo/issues/474
 
 // errorcheck
 
@@ -11,7 +11,7 @@
 package main
 
 func f(x interface{}) {
-	switch t := x.(type) {  case int: } // ERROR "declared and not used"
+	switch t := x.(type) {  case int: } // ERROR "declared but not used"
 }
 
 func g(x interface{}) {

test/compare/testdata/github.com-golang-go/fixedbugs/bug421.go

@@ -1,4 +1,4 @@
-// skip : false positive 'x declared and not used'
+// skip : false positive 'x declared but not used'
 
 // errorcheck
 

test/compare/testdata/github.com-golang-go/typeswitch2.go

@@ -40,9 +40,9 @@ func whatis(x interface{}) string {
 
 func notused(x interface{}) {
 	// The first t is in a different scope than the 2nd t; it cannot
-	// be accessed (=> declared and not used error); but it is legal
+	// be accessed (=> declared but not used error); but it is legal
 	// to declare it.
-	switch t := 0; t := x.(type) { // ERROR "declared and not used"
+	switch t := 0; t := x.(type) { // ERROR "declared but not used"
 	case int:
 		_ = t // this is using the t of "t := x.(type)"
 	}