internal/lsp: suggest completions that satisfy interfaces

When checking if a completion candidate matches the expected type at
the cursor position, we now use types.AssignableTo instead of
types.Identical. This properly handles cases like using a concrete
type to satisfy an interface type.

Calling AssignableTo triggered some crashes related to the fake
"resolved" types we create. Their underlying type was nil, which is
not allowed. We now set their underlying type to the invalid type.

I've also rearranged things so expected type information lives in a
dedicated typeInference struct. For now there is no new information added,
but in subsequent commits there will be more metadata about the
expected type.

Change-Id: I14e537c548960c30e444cf512a4413d75bb3ee45
GitHub-Last-Rev: 7e64ebe32938562648938d7a480195d954b018f2
GitHub-Pull-Request: golang/tools#116
Reviewed-on: https://go-review.googlesource.com/c/tools/+/182358
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/completion.go

@@ -130,17 +130,13 @@ type completer struct {
 	// surrounding describes the identifier surrounding the position.
 	surrounding *Selection
 
-	// expectedType is the type we expect the completion candidate to be.
-	// It may not be set.
-	expectedType types.Type
+	// expectedType conains information about the type we expect the completion
+	// candidate to be. It will be the zero value if no information is available.
+	expectedType typeInference
 
 	// enclosingFunction is the function declaration enclosing the position.
 	enclosingFunction *types.Signature
 
-	// preferTypeNames is true if we are completing at a position that expects a type,
-	// not a value.
-	preferTypeNames bool
-
 	// enclosingCompositeLiteral contains information about the composite literal
 	// enclosing the position.
 	enclosingCompositeLiteral *compLitInfo
@@ -205,10 +201,10 @@ func (c *completer) found(obj types.Object, weight float64) {
 		return
 	}
 	c.seen[obj] = true
-	if c.matchingType(obj.Type()) {
+	if c.matchingType(obj) {
 		weight *= highScore
 	}
-	if _, ok := obj.(*types.TypeName); !ok && c.preferTypeNames {
+	if c.wantTypeName() && !isTypeName(obj) {
 		weight *= lowScore
 	}
 	c.items = append(c.items, c.item(obj, weight))
@@ -258,7 +254,6 @@ func Completion(ctx context.Context, f GoFile, pos token.Pos) ([]CompletionItem,
 		pos:                       pos,
 		seen:                      make(map[types.Object]bool),
 		enclosingFunction:         enclosingFunction(path, pos, pkg.GetTypesInfo()),
-		preferTypeNames:           preferTypeNames(path, pos),
 		enclosingCompositeLiteral: clInfo,
 	}
 
@@ -344,6 +339,10 @@ func (c *completer) wantStructFieldCompletions() bool {
 	return clInfo.isStruct() && (clInfo.inKey || clInfo.maybeInFieldName)
 }
 
+func (c *completer) wantTypeName() bool {
+	return c.expectedType.wantTypeName
+}
+
 // selector finds completions for the specified selector expression.
 func (c *completer) selector(sel *ast.SelectorExpr) error {
 	// Is sel a qualified identifier?
@@ -657,10 +656,25 @@ const (
 	chanRead                        // channel read ("<-") operator
 )
 
-// expectedType returns the expected type for an expression at the query position.
-func expectedType(c *completer) types.Type {
+// typeInference holds information we have inferred about a type that can be
+// used at the current position.
+type typeInference struct {
+	// objType is the desired type of an object used at the query position.
+	objType types.Type
+
+	// wantTypeName is true if we expect the name of a type.
+	wantTypeName bool
+}
+
+// expectedType returns information about the expected type for an expression at
+// the query position.
+func expectedType(c *completer) typeInference {
+	if ti := expectTypeName(c); ti.wantTypeName {
+		return ti
+	}
+
 	if c.enclosingCompositeLiteral != nil {
-		return c.expectedCompositeLiteralType()
+		return typeInference{objType: c.expectedCompositeLiteralType()}
 	}
 
 	var (
@@ -693,14 +707,14 @@ Nodes:
 					break Nodes
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.CallExpr:
 			// Only consider CallExpr args if position falls between parens.
 			if node.Lparen <= c.pos && c.pos <= node.Rparen {
 				if tv, ok := c.info.Types[node.Fun]; ok {
 					if sig, ok := tv.Type.(*types.Signature); ok {
 						if sig.Params().Len() == 0 {
-							return nil
+							return typeInference{}
 						}
 						i := indexExprAtPos(c.pos, node.Args)
 						// Make sure not to run past the end of expected parameters.
@@ -712,7 +726,7 @@ Nodes:
 					}
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.ReturnStmt:
 			if sig := c.enclosingFunction; sig != nil {
 				// Find signature result that corresponds to our return statement.
@@ -723,7 +737,7 @@ Nodes:
 					}
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.CaseClause:
 			if swtch, ok := findSwitchStmt(c.path[i+1:], c.pos, node).(*ast.SwitchStmt); ok {
 				if tv, ok := c.info.Types[swtch.Tag]; ok {
@@ -731,14 +745,14 @@ Nodes:
 					break Nodes
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.SliceExpr:
 			// Make sure position falls within the brackets (e.g. "foo[a:<>]").
 			if node.Lbrack < c.pos && c.pos <= node.Rbrack {
 				typ = types.Typ[types.Int]
 				break Nodes
 			}
-			return nil
+			return typeInference{}
 		case *ast.IndexExpr:
 			// Make sure position falls within the brackets (e.g. "foo[<>]").
 			if node.Lbrack < c.pos && c.pos <= node.Rbrack {
@@ -749,12 +763,12 @@ Nodes:
 					case *types.Slice, *types.Array:
 						typ = types.Typ[types.Int]
 					default:
-						return nil
+						return typeInference{}
 					}
 					break Nodes
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.SendStmt:
 			// Make sure we are on right side of arrow (e.g. "foo <- <>").
 			if c.pos > node.Arrow+1 {
@@ -765,7 +779,7 @@ Nodes:
 					}
 				}
 			}
-			return nil
+			return typeInference{}
 		case *ast.StarExpr:
 			modifiers = append(modifiers, dereference)
 		case *ast.UnaryExpr:
@@ -777,7 +791,7 @@ Nodes:
 			}
 		default:
 			if breaksExpectedTypeInference(node) {
-				return nil
+				return typeInference{}
 			}
 		}
 	}
@@ -798,7 +812,9 @@ Nodes:
 		}
 	}
 
-	return typ
+	return typeInference{
+		objType: typ,
+	}
 }
 
 // findSwitchStmt returns an *ast.CaseClause's corresponding *ast.SwitchStmt or
@@ -837,50 +853,74 @@ func breaksExpectedTypeInference(n ast.Node) bool {
 	}
 }
 
-// preferTypeNames checks if given token position is inside func receiver,
-// type params, or type results. For example:
-//
-// func (<>) foo(<>) (<>) {}
-//
-func preferTypeNames(path []ast.Node, pos token.Pos) bool {
-	for i, p := range path {
+// expectTypeName returns information about the expected type name at position.
+func expectTypeName(c *completer) typeInference {
+	var wantTypeName bool
+
+Nodes:
+	for i, p := range c.path {
 		switch n := p.(type) {
 		case *ast.FuncDecl:
-			if r := n.Recv; r != nil && r.Pos() <= pos && pos <= r.End() {
-				return true
+			// Expect type names in a function declaration receiver, params and results.
+
+			if r := n.Recv; r != nil && r.Pos() <= c.pos && c.pos <= r.End() {
+				wantTypeName = true
+				break Nodes
 			}
 			if t := n.Type; t != nil {
-				if p := t.Params; p != nil && p.Pos() <= pos && pos <= p.End() {
-					return true
+				if p := t.Params; p != nil && p.Pos() <= c.pos && c.pos <= p.End() {
+					wantTypeName = true
+					break Nodes
 				}
-				if r := t.Results; r != nil && r.Pos() <= pos && pos <= r.End() {
-					return true
+				if r := t.Results; r != nil && r.Pos() <= c.pos && c.pos <= r.End() {
+					wantTypeName = true
+					break Nodes
 				}
 			}
-			return false
+			return typeInference{}
 		case *ast.CaseClause:
-			_, isTypeSwitch := findSwitchStmt(path[i+1:], pos, n).(*ast.TypeSwitchStmt)
-			return isTypeSwitch
+			// Expect type names in type switch case clauses.
+			if _, ok := findSwitchStmt(c.path[i+1:], c.pos, n).(*ast.TypeSwitchStmt); ok {
+				wantTypeName = true
+				break Nodes
+			}
+			return typeInference{}
 		case *ast.TypeAssertExpr:
-			if n.Lparen < pos && pos <= n.Rparen {
-				return true
+			// Expect type names in type assert expressions.
+			if n.Lparen < c.pos && c.pos <= n.Rparen {
+				wantTypeName = true
+				break Nodes
+			}
+			return typeInference{}
+		default:
+			if breaksExpectedTypeInference(p) {
+				return typeInference{}
 			}
 		}
 	}
-	return false
-}
 
-// matchingTypes reports whether actual is a good candidate type
-// for a completion in a context of the expected type.
-func (c *completer) matchingType(actual types.Type) bool {
-	if c.expectedType == nil {
-		return false
+	return typeInference{
+		wantTypeName: wantTypeName,
 	}
+}
+
+// matchingType reports whether an object is a good completion candidate
+// in the context of the expected type.
+func (c *completer) matchingType(obj types.Object) bool {
+	actual := obj.Type()
+
 	// Use a function's return type as its type.
 	if sig, ok := actual.(*types.Signature); ok {
 		if sig.Results().Len() == 1 {
 			actual = sig.Results().At(0).Type()
 		}
 	}
-	return types.Identical(types.Default(c.expectedType), types.Default(actual))
+
+	if c.expectedType.objType != nil {
+		// AssignableTo covers the case where the types are equal, but also handles
+		// cases like assigning a concrete type to an interface type.
+		return types.AssignableTo(types.Default(actual), types.Default(c.expectedType.objType))
+	}
+
+	return false
 }

internal/lsp/source/util.go

@@ -74,7 +74,7 @@ func resolveInvalid(obj types.Object, node ast.Node, info *types.Info) types.Obj
 		default:
 			return nil
 		}
-		typ := types.NewNamed(types.NewTypeName(token.NoPos, obj.Pkg(), typename, nil), nil, nil)
+		typ := types.NewNamed(types.NewTypeName(token.NoPos, obj.Pkg(), typename, nil), types.Typ[types.Invalid], nil)
 		return types.NewVar(obj.Pos(), obj.Pkg(), obj.Name(), typ)
 	}
 	var resultExpr ast.Expr
@@ -127,6 +127,11 @@ func deref(typ types.Type) types.Type {
 	return typ
 }
 
+func isTypeName(obj types.Object) bool {
+	_, ok := obj.(*types.TypeName)
+	return ok
+}
+
 func formatParams(tup *types.Tuple, variadic bool, qf types.Qualifier) []string {
 	params := make([]string, 0, tup.Len())
 	for i := 0; i < tup.Len(); i++ {

internal/lsp/testdata/interfacerank/interface_rank.go

@@ -0,0 +1,20 @@
+package interfacerank
+
+type foo interface {
+	foo()
+}
+
+type fooImpl int
+
+func (*fooImpl) foo() {}
+
+func wantsFoo(foo) {}
+
+func _() {
+	var (
+		aa string   //@item(irAA, "aa", "string", "var")
+		ab *fooImpl //@item(irAB, "ab", "*fooImpl", "var")
+	)
+
+	wantsFoo(a) //@complete(")", irAB, irAA)
+}

internal/lsp/testdata/unresolved/unresolved.go.in

@@ -0,0 +1,6 @@
+package unresolved
+
+func foo(interface{}) { //@item(unresolvedFoo, "foo(interface{})", "", "func")
+	// don't crash on fake "resolved" type
+	foo(func(i, j f //@complete(" //", unresolvedFoo)
+}

internal/lsp/tests/tests.go

@@ -25,7 +25,7 @@ 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       = 122
+	ExpectedCompletionsCount       = 124
 	ExpectedCompletionSnippetCount = 14
 	ExpectedDiagnosticsCount       = 17
 	ExpectedFormatCount            = 5