internal/lsp: fix scope of FuncType completion candidates

Fix objects defined in the function signature to only be completable
inside the function body. For example:

func (dog Dog) bark(d<>) { // Don't complete <> to "dog".
  d<> // Do complete <> to "dog".
}

Change-Id: Ic9a2dc2ce6771212780f2d6af2221a67d203f35f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/196559
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>

Author: muirdm

internal/lsp/source/completion.go

@@ -563,11 +563,16 @@ func (c *completer) methodsAndFields(typ types.Type, addressable bool) error {
 func (c *completer) lexical() error {
 	var scopes []*types.Scope // scopes[i], where i<len(path), is the possibly nil Scope of path[i].
 	for _, n := range c.path {
+		// Include *FuncType scope if pos is inside the function body.
 		switch node := n.(type) {
 		case *ast.FuncDecl:
-			n = node.Type
+			if node.Body != nil && nodeContains(node.Body, c.pos) {
+				n = node.Type
+			}
 		case *ast.FuncLit:
-			n = node.Type
+			if node.Body != nil && nodeContains(node.Body, c.pos) {
+				n = node.Type
+			}
 		}
 		scopes = append(scopes, c.pkg.GetTypesInfo().Scopes[n])
 	}
@@ -654,6 +659,10 @@ func (c *completer) lexical() error {
 	return nil
 }
 
+func nodeContains(n ast.Node, pos token.Pos) bool {
+	return n != nil && n.Pos() <= pos && pos < n.End()
+}
+
 func (c *completer) inConstDecl() bool {
 	for _, n := range c.path {
 		if decl, ok := n.(*ast.GenDecl); ok && decl.Tok == token.CONST {

internal/lsp/testdata/funcsig/func_sig.go

@@ -0,0 +1,9 @@
+package funcsig
+
+type someType int //@item(sigSomeType, "someType", "int", "type")
+
+// Don't complete "foo" in signature.
+func (foo someType) _() { //@item(sigFoo, "foo", "someType", "var"),complete(") {", sigSomeType)
+
+	//@complete("", sigFoo, sigSomeType)
+}

internal/lsp/tests/tests.go

@@ -29,7 +29,7 @@ import (
 // We hardcode the expected number of test cases to ensure that all tests
 // are being executed. If a test is added, this number must be changed.
 const (
-	ExpectedCompletionsCount           = 152
+	ExpectedCompletionsCount           = 154
 	ExpectedCompletionSnippetCount     = 36
 	ExpectedUnimportedCompletionsCount = 1
 	ExpectedDeepCompletionsCount       = 5