go.tools/go/types: report init dependencies via method values

- one-line fix
- comprehensive set of test cases added

Fixes golang/go#7963.

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/100320043

go/types/call.go

@@ -408,6 +408,8 @@ func (check *checker) selector(x *operand, e *ast.SelectorExpr) {
 			sig.recv = nil
 			x.typ = &sig
 
+			check.addDeclDep(obj)
+
 		default:
 			unreachable()
 		}

go/types/check_test.go

@@ -57,6 +57,7 @@ var tests = [][]string{
 	{"testdata/cycles4.src"},
 	{"testdata/init0.src"},
 	{"testdata/init1.src"},
+	{"testdata/init2.src"},
 	{"testdata/decls0.src"},
 	{"testdata/decls1.src"},
 	{"testdata/decls2a.src", "testdata/decls2b.src"},

go/types/testdata/init0.src

@@ -96,11 +96,11 @@ func (T1) m() bool { _ = x11; return false }
 
 var x11 /* ERROR initialization cycle */ = T1.m(T1{})
 
-// no cycles via method values
+// cycles via method values
 
 type T2 struct{}
 
 func (T2) m() bool { _ = x12; return false }
 
 var t1 T2
-var x12 = t1.m
+var x12 /* ERROR initialization cycle */ = t1.m

go/types/testdata/init1.src

@@ -14,7 +14,7 @@ func (T0) m() int { return y0 }
 
 var x0 = T0{}
 
-var y0 = x0.m() // no cycle reported
+var y0 /* ERROR initialization cycle */ = x0.m()
 
 type T1 struct{}
 
@@ -24,7 +24,7 @@ var x1 interface {
 	m() int
 } = T1{}
 
-var y1 = x1.m() // no cycle reported
+var y1 = x1.m() // no cycle reported, x1 is of interface type
 
 // issue 6703 (modified)
 
@@ -50,7 +50,7 @@ func (T3) m() int {
 	return 0
 }
 
-var x4 = T4{}.m // <<<< added {}
+var x4 /* ERROR initialization cycle */ = T4{}.m // <<<< added {}
 
 var y4 = x4
 
@@ -61,7 +61,7 @@ func (T4) m() int {
 	return 0
 }
 
-var x5 = T5{}.m() // <<<< added ()
+var x5 /* ERROR initialization cycle */ = T5{}.m() // <<<< added ()
 
 var y5 = x5
 

go/types/testdata/init2.src

@@ -0,0 +1,139 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// initialization cycles
+
+package init2
+
+// cycles through functions
+
+func f1() int { _ = x1; return 0 }
+var x1 /* ERROR initialization cycle */ = f1
+
+func f2() int { _ = x2; return 0 }
+var x2 /* ERROR initialization cycle */ = f2()
+
+// cycles through method expressions
+
+type T3 int
+func (T3) m() int { _ = x3; return 0 }
+var x3 /* ERROR initialization cycle */ = T3.m
+
+type T4 int
+func (T4) m() int { _ = x4; return 0 }
+var x4 /* ERROR initialization cycle */ = T4.m(0)
+
+type T3p int
+func (*T3p) m() int { _ = x3p; return 0 }
+var x3p /* ERROR initialization cycle */ = (*T3p).m
+
+type T4p int
+func (*T4p) m() int { _ = x4p; return 0 }
+var x4p /* ERROR initialization cycle */ = (*T4p).m(nil)
+
+// cycles through method expressions of embedded methods
+
+type T5 struct { E5 }
+type E5 int
+func (E5) m() int { _ = x5; return 0 }
+var x5 /* ERROR initialization cycle */ = T5.m
+
+type T6 struct { E6 }
+type E6 int
+func (E6) m() int { _ = x6; return 0 }
+var x6 /* ERROR initialization cycle */ = T6.m(T6{0})
+
+type T5p struct { E5p }
+type E5p int
+func (*E5p) m() int { _ = x5p; return 0 }
+var x5p /* ERROR initialization cycle */ = (*T5p).m
+
+type T6p struct { E6p }
+type E6p int
+func (*E6p) m() int { _ = x6p; return 0 }
+var x6p /* ERROR initialization cycle */ = (*T6p).m(nil)
+
+// cycles through method values
+
+type T7 int
+func (T7) m() int { _ = x7; return 0 }
+var x7 /* ERROR initialization cycle */ = T7(0).m
+
+type T8 int
+func (T8) m() int { _ = x8; return 0 }
+var x8 /* ERROR initialization cycle */ = T8(0).m()
+
+type T7p int
+func (*T7p) m() int { _ = x7p; return 0 }
+var x7p /* ERROR initialization cycle */ = new(T7p).m
+
+type T8p int
+func (*T8p) m() int { _ = x8p; return 0 }
+var x8p /* ERROR initialization cycle */ = new(T8p).m()
+
+type T7v int
+func (T7v) m() int { _ = x7v; return 0 }
+var x7var T7v
+var x7v /* ERROR initialization cycle */ = x7var.m
+
+type T8v int
+func (T8v) m() int { _ = x8v; return 0 }
+var x8var T8v
+var x8v /* ERROR initialization cycle */ = x8var.m()
+
+type T7pv int
+func (*T7pv) m() int { _ = x7pv; return 0 }
+var x7pvar *T7pv
+var x7pv /* ERROR initialization cycle */ = x7pvar.m
+
+type T8pv int
+func (*T8pv) m() int { _ = x8pv; return 0 }
+var x8pvar *T8pv
+var x8pv /* ERROR initialization cycle */ = x8pvar.m()
+
+// cycles through method values of embedded methods
+
+type T9 struct { E9 }
+type E9 int
+func (E9) m() int { _ = x9; return 0 }
+var x9 /* ERROR initialization cycle */ = T9{0}.m
+
+type T10 struct { E10 }
+type E10 int
+func (E10) m() int { _ = x10; return 0 }
+var x10 /* ERROR initialization cycle */ = T10{0}.m()
+
+type T9p struct { E9p }
+type E9p int
+func (*E9p) m() int { _ = x9p; return 0 }
+var x9p /* ERROR initialization cycle */ = new(T9p).m
+
+type T10p struct { E10p }
+type E10p int
+func (*E10p) m() int { _ = x10p; return 0 }
+var x10p /* ERROR initialization cycle */ = new(T10p).m()
+
+type T9v struct { E9v }
+type E9v int
+func (E9v) m() int { _ = x9v; return 0 }
+var x9var T9v
+var x9v /* ERROR initialization cycle */ = x9var.m
+
+type T10v struct { E10v }
+type E10v int
+func (E10v) m() int { _ = x10v; return 0 }
+var x10var T10v
+var x10v /* ERROR initialization cycle */ = x10var.m()
+
+type T9pv struct { E9pv }
+type E9pv int
+func (*E9pv) m() int { _ = x9pv; return 0 }
+var x9pvar *T9pv
+var x9pv /* ERROR initialization cycle */ = x9pvar.m
+
+type T10pv struct { E10pv }
+type E10pv int
+func (*E10pv) m() int { _ = x10pv; return 0 }
+var x10pvar *T10pv
+var x10pv /* ERROR initialization cycle */ = x10pvar.m()