go/types: fix Info.Implicits entries

Packages of dot imports don't appear in the Info.Implicits map
since they are already taken care of by the Info.Defs map. Fix
documentation.

Implicitly dot-imported objects of a package shouldn't appear
in the Info.Implicits map because the documentation never said
so and there's no way to map multiple objects to the same
*ast.ImportSpec with the current data structure.

Added missing test for Info.Implicits.

The fix is a trivial one-line deletion, the rest is documentation
and test.

Fixes #21591.

Change-Id: I12a37dab85c531911c9363ec3d58daa095c7eb24
Reviewed-on: https://go-review.googlesource.com/60672Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/api.go

@@ -176,11 +176,11 @@ type Info struct {
 	// Implicits maps nodes to their implicitly declared objects, if any.
 	// The following node and object types may appear:
 	//
-	//	node               declared object
+	//     node               declared object
 	//
-	//	*ast.ImportSpec    *PkgName for dot-imports and imports without renames
-	//	*ast.CaseClause    type-specific *Var for each type switch case clause (incl. default)
-	//      *ast.Field         anonymous parameter *Var
+	//     *ast.ImportSpec    *PkgName for imports without renames
+	//     *ast.CaseClause    type-specific *Var for each type switch case clause (incl. default)
+	//     *ast.Field         anonymous parameter *Var
 	//
 	Implicits map[ast.Node]Object
 
@@ -200,16 +200,16 @@ type Info struct {
 	//
 	// The following node types may appear in Scopes:
 	//
-	//	*ast.File
-	//	*ast.FuncType
-	//	*ast.BlockStmt
-	//	*ast.IfStmt
-	//	*ast.SwitchStmt
-	//	*ast.TypeSwitchStmt
-	//	*ast.CaseClause
-	//	*ast.CommClause
-	//	*ast.ForStmt
-	//	*ast.RangeStmt
+	//     *ast.File
+	//     *ast.FuncType
+	//     *ast.BlockStmt
+	//     *ast.IfStmt
+	//     *ast.SwitchStmt
+	//     *ast.TypeSwitchStmt
+	//     *ast.CaseClause
+	//     *ast.CommClause
+	//     *ast.ForStmt
+	//     *ast.RangeStmt
 	//
 	Scopes map[ast.Node]*Scope
 

src/go/types/api_test.go

@@ -257,6 +257,63 @@ func TestTypesInfo(t *testing.T) {
 	}
 }
 
+func TestImplicitsInfo(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	var tests = []struct {
+		src  string
+		want string
+	}{
+		{`package p2; import . "fmt"; var _ = Println`, ""},           // no Implicits entry
+		{`package p0; import local "fmt"; var _ = local.Println`, ""}, // no Implicits entry
+		{`package p1; import "fmt"; var _ = fmt.Println`, "importSpec: package fmt"},
+
+		{`package p3; func f(x interface{}) { switch x.(type) { case int: } }`, ""}, // no Implicits entry
+		{`package p4; func f(x interface{}) { switch t := x.(type) { case int: _ = t } }`, "caseClause: var t int"},
+		{`package p5; func f(x interface{}) { switch t := x.(type) { case int, uint: _ = t } }`, "caseClause: var t interface{}"},
+		{`package p6; func f(x interface{}) { switch t := x.(type) { default: _ = t } }`, "caseClause: var t interface{}"},
+
+		{`package p7; func f(x int) {}`, ""}, // no Implicits entry
+		{`package p8; func f(int) {}`, "field: var  int"},
+		{`package p9; func f() (complex64) { return 0 }`, "field: var  complex64"},
+		{`package p10; type T struct{}; func (*T) f() {}`, "field: var  *p10.T"},
+	}
+
+	for _, test := range tests {
+		info := Info{
+			Implicits: make(map[ast.Node]Object),
+		}
+		name := mustTypecheck(t, "ImplicitsInfo", test.src, &info)
+
+		// the test cases expect at most one Implicits entry
+		if len(info.Implicits) > 1 {
+			t.Errorf("package %s: %d Implicits entries found", name, len(info.Implicits))
+			continue
+		}
+
+		// extract Implicits entry, if any
+		var got string
+		for n, obj := range info.Implicits {
+			switch x := n.(type) {
+			case *ast.ImportSpec:
+				got = "importSpec"
+			case *ast.CaseClause:
+				got = "caseClause"
+			case *ast.Field:
+				got = "field"
+			default:
+				t.Fatalf("package %s: unexpected %T", name, x)
+			}
+			got += ": " + obj.String()
+		}
+
+		// verify entry
+		if got != test.want {
+			t.Errorf("package %s: got %q; want %q", name, got, test.want)
+		}
+	}
+}
+
 func predString(tv TypeAndValue) string {
 	var buf bytes.Buffer
 	pred := func(b bool, s string) {

src/go/types/resolver.go

@@ -303,7 +303,6 @@ func (check *Checker) collectObjects() {
 									// via Config.Packages - may be dot-imported in
 									// another package!)
 									check.declare(fileScope, nil, obj, token.NoPos)
-									check.recordImplicit(s, obj)
 								}
 							}
 							// add position to set of dot-import positions for this file