internal/refactor/inline: improve a confusing error message

Change-Id: I31e587105ffd16dbe32436ce5a090180f5186200
Reviewed-on: https://go-review.googlesource.com/c/tools/+/554061
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

internal/refactor/inline/inline.go

@@ -485,7 +485,7 @@ func inline(logf func(string, ...any), caller *Caller, callee *gobCallee) (*resu
 			// check not shadowed at caller.
 			found := caller.lookup(obj.Name) // always finds something
 			if found.Pos().IsValid() {
-				return nil, fmt.Errorf("cannot inline because built-in %q is shadowed in caller by a %s (line %d)",
+				return nil, fmt.Errorf("cannot inline, because the callee refers to built-in %q, which in the caller is shadowed by a %s (declared at line %d)",
 					obj.Name, objectKind(found),
 					caller.Fset.PositionFor(found.Pos(), false).Line)
 			}
@@ -505,8 +505,9 @@ func inline(logf func(string, ...any), caller *Caller, callee *gobCallee) (*resu
 					// around the refactored signature.
 					found := caller.lookup(obj.Name)
 					if found != nil && !isPkgLevel(found) {
-						return nil, fmt.Errorf("cannot inline because %q is shadowed in caller by a %s (line %d)",
-							obj.Name, objectKind(found),
+						return nil, fmt.Errorf("cannot inline, because the callee refers to %s %q, which in the caller is shadowed by a %s (declared at line %d)",
+							obj.Kind, obj.Name,
+							objectKind(found),
 							caller.Fset.PositionFor(found.Pos(), false).Line)
 					}
 				} else {

internal/refactor/inline/testdata/err-shadow-builtin.txtar

@@ -10,7 +10,7 @@ package a
 
 func _() {
 	const nil = 1
-	_ = f() //@ inline(re"f", re"nil.*shadowed.*by.*const .line 4")
+	_ = f() //@ inline(re"f", re"nil.*shadowed.*by.*const.*line 4")
 }
 
 func f() *int { return nil }
@@ -20,7 +20,7 @@ package a
 
 func _() {
 	type append int
-	g(nil) //@ inline(re"g", re"append.*shadowed.*by.*typename .line 4")
+	g(nil) //@ inline(re"g", re"append.*shadowed.*by.*typename.*line 4")
 }
 
 func g(x []int) { _ = append(x, x...) }
@@ -30,7 +30,7 @@ package a
 
 func _() {
 	type int uint8
-	_ = h(0) //@ inline(re"h", re"int.*shadowed.*by.*typename .line 4")
+	_ = h(0) //@ inline(re"h", re"int.*shadowed.*by.*typename.*line 4")
 }
 
 func h(x int) int { return x + 1 }

internal/refactor/inline/testdata/err-shadow-pkg.txtar

@@ -15,7 +15,7 @@ package a
 func _() {
 	f() //@ inline(re"f", result)
 	const v = 1
-	f() //@ inline(re"f", re"v.*shadowed.*by.*const .line 5")
+	f() //@ inline(re"f", re"v.*shadowed.*by.*const.*line 5")
 }
 
 func f() int { return v }
@@ -28,7 +28,7 @@ package a
 func _() {
 	_ = v //@ inline(re"f", result)
 	const v = 1
-	f() //@ inline(re"f", re"v.*shadowed.*by.*const .line 5")
+	f() //@ inline(re"f", re"v.*shadowed.*by.*const.*line 5")
 }
 
 func f() int { return v }