go/types: improve errors for method calls with pointer receivers

The compiler has better error messages for methods called without a
pointer receiver when one is expected. This change is similar to
CL 229801, but for method calls.

Also, added better error messages for functions called with the wrong
capitalization. I left the third TODO in this switch statement almost
as-is because I'm not sure that the extra complexity is worth it -
I adjusted the error to look like the one the compiler reports.

Fixes golang/go#38658

Change-Id: Ie0ca2503e12f3659f112f0135cc27db1b027fdcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/230380
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/call.go

@@ -9,6 +9,7 @@ package types
 import (
 	"go/ast"
 	"go/token"
+	"unicode"
 )
 
 func (check *Checker) call(x *operand, e *ast.CallExpr) exprKind {
@@ -375,12 +376,24 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 		switch {
 		case index != nil:
 			// TODO(gri) should provide actual type where the conflict happens
-			check.errorf(e.Sel.Pos(), "ambiguous selector %s", sel)
+			check.errorf(e.Sel.Pos(), "ambiguous selector %s.%s", x.expr, sel)
 		case indirect:
-			// TODO(gri) be more specific with this error message
-			check.errorf(e.Sel.Pos(), "%s is not in method set of %s", sel, x.typ)
+			check.errorf(e.Sel.Pos(), "cannot call pointer method %s on %s", sel, x.typ)
 		default:
-			// TODO(gri) should check if capitalization of sel matters and provide better error message in that case
+			// Check if capitalization of sel matters and provide better error
+			// message in that case.
+			if len(sel) > 0 {
+				var changeCase string
+				if r := rune(sel[0]); unicode.IsUpper(r) {
+					changeCase = string(unicode.ToLower(r)) + sel[1:]
+				} else {
+					changeCase = string(unicode.ToUpper(r)) + sel[1:]
+				}
+				if obj, _, _ = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
+					check.errorf(e.Sel.Pos(), "%s.%s undefined (type %s has no field or method %s, but does have %s)", x.expr, sel, x.typ, sel, changeCase)
+					break
+				}
+			}
 			check.errorf(e.Sel.Pos(), "%s.%s undefined (type %s has no field or method %s)", x.expr, sel, x.typ, sel)
 		}
 		goto Error

src/go/types/testdata/decls3.src

@@ -19,7 +19,7 @@ func _() {
 	)
 
 	var t T3
-	_ = t.X /* ERROR "ambiguous selector" */
+	_ = t.X /* ERROR "ambiguous selector t.X" */
 }
 
 func _() {
@@ -31,7 +31,7 @@ func _() {
 	)
 
 	var t T4
-	_ = t.X /* ERROR "ambiguous selector" */
+	_ = t.X /* ERROR "ambiguous selector t.X" */
 }
 
 func issue4355() {
@@ -44,7 +44,7 @@ func issue4355() {
 	)
 
 	var t T5
-	_ = t.X /* ERROR "ambiguous selector" */
+	_ = t.X /* ERROR "ambiguous selector t.X" */
 }
 
 func _() {
@@ -54,7 +54,7 @@ func _() {
 	type T struct{ A; B }
 
 	var t T
-	_ = t.State /* ERROR "ambiguous selector" */
+	_ = t.State /* ERROR "ambiguous selector t.State" */
 }
 
 // Embedded fields can be predeclared types.
@@ -221,16 +221,16 @@ func _() {
 	_ = S2{}.B
 	_ = S2{}.C
 	_ = S2{}.D /* ERROR "no field or method" */
-	_ = S3{}.S1 /* ERROR "ambiguous selector" */
+	_ = S3{}.S1 /* ERROR "ambiguous selector \(S3 literal\).S1" */
 	_ = S3{}.A
-	_ = S3{}.B /* ERROR "ambiguous selector" */
+	_ = S3{}.B /* ERROR "ambiguous selector" \(S3 literal\).B */
 	_ = S3{}.D
 	_ = S3{}.E
 	_ = S4{}.A
 	_ = S4{}.B /* ERROR "no field or method" */
-	_ = S5{}.X /* ERROR "ambiguous selector" */
+	_ = S5{}.X /* ERROR "ambiguous selector \(S5 literal\).X" */
 	_ = S5{}.Y
-	_ = S10{}.X /* ERROR "ambiguous selector" */
+	_ = S10{}.X /* ERROR "ambiguous selector \(S10 literal\).X" */
 	_ = S10{}.Y
 }
 
@@ -306,4 +306,4 @@ type R22 R21
 type R23 R21
 type R24 R21
 
-var _ = R0{}.X /* ERROR "ambiguous selector" */
+var _ = R0{}.X /* ERROR "ambiguous selector \(R0 literal\).X" */

src/go/types/testdata/decls4.src

@@ -190,8 +190,8 @@ type eD struct {
 }
 
 var (
-	_ = eD{}.xf /* ERROR ambiguous selector */
-	_ = eD{}.xm /* ERROR ambiguous selector */
+	_ = eD{}.xf /* ERROR ambiguous selector \(eD literal\).xf */
+	_ = eD{}.xm /* ERROR ambiguous selector \(eD literal\).xm */
 )
 
 var (

src/go/types/testdata/expr3.src

@@ -155,10 +155,10 @@ func (*T) m() {}
 func method_expressions() {
 	_ = T.a /* ERROR "no field or method" */
 	_ = T.x /* ERROR "has no method" */
-	_ = T.m /* ERROR "not in method set" */
+	_ = T.m /* ERROR "cannot call pointer method m on T" */
 	_ = (*T).m
 
-	var f func(*T) = T.m /* ERROR "not in method set" */
+	var f func(*T) = T.m /* ERROR "cannot call pointer method m on T" */
 	var g func(*T) = (*T).m
 	_, _ = f, g
 

src/go/types/testdata/issue28251.src

@@ -41,7 +41,7 @@ type (
 )
 
 func (T4) m4() {}
-func _() { (T{}).m4 /* ERROR m4 is not in method set of T */ () }
+func _() { (T{}).m4 /* ERROR "cannot call pointer method m4 on T" */ () }
 func _() { (&T{}).m4() }
 
 type (
@@ -51,7 +51,7 @@ type (
 )
 
 func (T6) m6() {}
-func _() { (T{}).m6 /* ERROR m6 is not in method set of T */ () }
+func _() { (T{}).m6 /* ERROR "cannot call pointer method m6 on T" */ () }
 func _() { (&T{}).m6() }
 
 type (

src/go/types/testdata/issues.src

@@ -130,9 +130,13 @@ func issue10260() {
 		t2 *T2
 	)
 
-	var x I1 = T1 /* ERROR cannot use .*: missing method foo \(foo has pointer receiver\) */ {}
+	var x I1
+	x = T1 /* ERROR cannot use .*: missing method foo \(foo has pointer receiver\) */ {}
 	_ = x /* ERROR .* cannot have dynamic type T1 \(missing method foo \(foo has pointer receiver\)\) */ .(T1)
 
+	T1{}.foo /* ERROR cannot call pointer method foo on T1 */ ()
+	x.Foo /* ERROR "x.Foo undefined \(type I1 has no field or method Foo, but does have foo\)" */ ()
+
 	_ = i2 /* ERROR i2 .* cannot have dynamic type \*T1 \(wrong type for method foo \(have func\(\), want func\(x int\)\)\) */ .(*T1)
 
 	i1 = i0 /* ERROR cannot use .* missing method foo */
@@ -341,7 +345,7 @@ type E1 struct{ f int }
 type E2 struct{ f int }
 
 func issue26234b(x T) {
-	_ = x.f /* ERROR ambiguous selector f */
+	_ = x.f /* ERROR ambiguous selector x.f */
 }
 
 func issue26234c() {

src/go/types/testdata/methodsets.src

@@ -29,7 +29,7 @@ type T3 struct {
 func _() {
 	var (
 		_ func(T0) = T0.v0
-		_ = T0.p0 /* ERROR "not in method set" */
+		_ = T0.p0 /* ERROR "cannot call pointer method p0 on T0" */
 
 		_ func (*T0) = (*T0).v0
 		_ func (*T0) = (*T0).p0
@@ -40,7 +40,7 @@ func _() {
 		_ func(T2) = T2.p2
 
 		_ func(T3) = T3.v0
-		_ func(T3) = T3.p0 /* ERROR "not in method set" */
+		_ func(T3) = T3.p0 /* ERROR "cannot call pointer method p0 on T3" */
 		_ func(T3) = T3.v1
 		_ func(T3) = T3.p1
 		_ func(T3) = T3.v2
@@ -135,7 +135,7 @@ func _() {
 func _() {
 	var (
 		_ func() = T0{}.v0
-		_ func() = T0{}.p0 /* ERROR "not in method set" */
+		_ func() = T0{}.p0 /* ERROR "cannot call pointer method p0 on T0" */
 
 		_ func() = (&T0{}).v0
 		_ func() = (&T0{}).p0
@@ -145,7 +145,7 @@ func _() {
 		// no values for T2
 
 		_ func() = T3{}.v0
-		_ func() = T3{}.p0 /* ERROR "not in method set" */
+		_ func() = T3{}.p0 /* ERROR "cannot call pointer method p0 on T3" */
 		_ func() = T3{}.v1
 		_ func() = T3{}.p1
 		_ func() = T3{}.v2
@@ -163,7 +163,7 @@ func _() {
 // Method calls with value receivers
 func _() {
 	T0{}.v0()
-	T0{}.p0 /* ERROR "not in method set" */ ()
+	T0{}.p0 /* ERROR "cannot call pointer method p0 on T0" */ ()
 
 	(&T0{}).v0()
 	(&T0{}).p0()
@@ -173,7 +173,7 @@ func _() {
 	// no values for T2
 
 	T3{}.v0()
-	T3{}.p0 /* ERROR "not in method set" */ ()
+	T3{}.p0 /* ERROR "cannot call pointer method p0 on T3" */ ()
 	T3{}.v1()
 	T3{}.p1()
 	T3{}.v2()