go/ast: import AST changes supporting typeparams from dev.go2go

Minimal changes are made to existing types in go/ast to support type
parameters. Namely:
 + FieldList is overloaded to hold type parameter lists. In this case,
   the field name becomes the type identifier, and the field type
   becomes the constraint.
 + FuncType and TypeSpec gain a TParams FieldList.
 + CallExpr gains a 'Brackets' flag, signaling that it uses '[]' rather
   than '()', representing a generic type expression with type
   parameters.

Modifications from dev.go2go: the 'UseBrackets' field was removed from
ast.File, as this support is no longer necessary.

Change-Id: I21fd7390f1800dece3c14e6ec015fb2419e9fc52
Reviewed-on: https://go-review.googlesource.com/c/go/+/264181
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>

src/go/ast/ast.go

@@ -188,11 +188,14 @@ func isDirective(c string) bool {
 // in a signature.
 // Field.Names is nil for unnamed parameters (parameter lists which only contain types)
 // and embedded struct fields. In the latter case, the field name is the type name.
+// Field.Names contains a single name "type" for elements of interface type lists.
+// Types belonging to the same type list share the same "type" identifier which also
+// records the position of that keyword.
 //
 type Field struct {
 	Doc     *CommentGroup // associated documentation; or nil
-	Names   []*Ident      // field/method/parameter names; or nil
+	Names   []*Ident      // field/method/(type) parameter names, or type "type"; or nil
-	Type    Expr          // field/method/parameter type
+	Type    Expr          // field/method/parameter type, type list type; or nil
 	Tag     *BasicLit     // field tag; or nil
 	Comment *CommentGroup // line comments; or nil
 }
@@ -201,14 +204,23 @@ func (f *Field) Pos() token.Pos {
 	if len(f.Names) > 0 {
 		return f.Names[0].Pos()
 	}
-	return f.Type.Pos()
+	if f.Type != nil {
+		return f.Type.Pos()
+	}
+	return token.NoPos
 }
 
 func (f *Field) End() token.Pos {
 	if f.Tag != nil {
 		return f.Tag.End()
 	}
-	return f.Type.End()
+	if f.Type != nil {
+		return f.Type.End()
+	}
+	if len(f.Names) > 0 {
+		return f.Names[len(f.Names)-1].End()
+	}
+	return token.NoPos
 }
 
 // A FieldList represents a list of Fields, enclosed by parentheses or braces.
@@ -242,7 +254,7 @@ func (f *FieldList) End() token.Pos {
 	return token.NoPos
 }
 
-// NumFields returns the number of parameters or struct fields represented by a FieldList.
+// NumFields returns the number of (type) parameters or struct fields represented by a FieldList.
 func (f *FieldList) NumFields() int {
 	n := 0
 	if f != nil {
@@ -285,12 +297,6 @@ type (
 	}
 
 	// A BasicLit node represents a literal of basic type.
-	//
-	// Note that for the CHAR and STRING kinds, the literal is stored
-	// with its quotes. For example, for a double-quoted STRING, the
-	// first and the last rune in the Value field will be ". The
-	// Unquote and UnquoteChar functions in the strconv package can be
-	// used to unquote STRING and CHAR values, respectively.
 	BasicLit struct {
 		ValuePos token.Pos   // literal position
 		Kind     token.Token // token.INT, token.FLOAT, token.IMAG, token.CHAR, or token.STRING
@@ -361,6 +367,7 @@ type (
 		Args     []Expr    // function arguments; or nil
 		Ellipsis token.Pos // position of "..." (token.NoPos if there is no "...")
 		Rparen   token.Pos // position of ")"
+		Brackets bool      // if set, "[" and "]" are used instead of "(" and ")"
 	}
 
 	// A StarExpr node represents an expression of the form "*" Expression.
@@ -432,6 +439,7 @@ type (
 	// A FuncType node represents a function type.
 	FuncType struct {
 		Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
+		TParams *FieldList // type parameters; or nil
 		Params  *FieldList // (incoming) parameters; non-nil
 		Results *FieldList // (outgoing) results; or nil
 	}
@@ -439,8 +447,8 @@ type (
 	// An InterfaceType node represents an interface type.
 	InterfaceType struct {
 		Interface  token.Pos  // position of "interface" keyword
-		Methods    *FieldList // list of methods
+		Methods    *FieldList // list of embedded interfaces, methods, or types
-		Incomplete bool       // true if (source) methods are missing in the Methods list
+		Incomplete bool       // true if (source) methods or types are missing in the Methods list
 	}
 
 	// A MapType node represents a map type.
@@ -893,6 +901,7 @@ type (
 	TypeSpec struct {
 		Doc     *CommentGroup // associated documentation; or nil
 		Name    *Ident        // type name
+		TParams *FieldList    // type parameters; or nil
 		Assign  token.Pos     // position of '=', if any
 		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
 		Comment *CommentGroup // line comments; or nil
@@ -960,7 +969,7 @@ type (
 	GenDecl struct {
 		Doc    *CommentGroup // associated documentation; or nil
 		TokPos token.Pos     // position of Tok
-		Tok    token.Token   // IMPORT, CONST, TYPE, VAR
+		Tok    token.Token   // IMPORT, CONST, TYPE, or VAR
 		Lparen token.Pos     // position of '(', if any
 		Specs  []Spec
 		Rparen token.Pos // position of ')', if any
@@ -971,11 +980,15 @@ type (
 		Doc  *CommentGroup // associated documentation; or nil
 		Recv *FieldList    // receiver (methods); or nil (functions)
 		Name *Ident        // function/method name
-		Type *FuncType     // function signature: parameters, results, and position of "func" keyword
+		Type *FuncType     // function signature: type and value parameters, results, and position of "func" keyword
 		Body *BlockStmt    // function body; or nil for external (non-Go) function
 	}
 )
 
+func (f *FuncDecl) IsMethod() bool {
+	return f.Recv.NumFields() != 0
+}
+
 // Pos and End implementations for declaration nodes.
 
 func (d *BadDecl) Pos() token.Pos  { return d.From }

src/go/ast/example_test.go

@@ -119,22 +119,23 @@ func main() {
 	//     40  .  .  .  .  .  .  .  }
 	//     41  .  .  .  .  .  .  .  Ellipsis: -
 	//     42  .  .  .  .  .  .  .  Rparen: 4:25
-	//     43  .  .  .  .  .  .  }
+	//     43  .  .  .  .  .  .  .  Brackets: false
-	//     44  .  .  .  .  .  }
+	//     44  .  .  .  .  .  .  }
-	//     45  .  .  .  .  }
+	//     45  .  .  .  .  .  }
-	//     46  .  .  .  .  Rbrace: 5:1
+	//     46  .  .  .  .  }
-	//     47  .  .  .  }
+	//     47  .  .  .  .  Rbrace: 5:1
-	//     48  .  .  }
+	//     48  .  .  .  }
-	//     49  .  }
+	//     49  .  .  }
-	//     50  .  Scope: *ast.Scope {
+	//     50  .  }
-	//     51  .  .  Objects: map[string]*ast.Object (len = 1) {
+	//     51  .  Scope: *ast.Scope {
-	//     52  .  .  .  "main": *(obj @ 11)
+	//     52  .  .  Objects: map[string]*ast.Object (len = 1) {
-	//     53  .  .  }
+	//     53  .  .  .  "main": *(obj @ 11)
-	//     54  .  }
+	//     54  .  .  }
-	//     55  .  Unresolved: []*ast.Ident (len = 1) {
+	//     55  .  }
-	//     56  .  .  0: *(obj @ 29)
+	//     56  .  Unresolved: []*ast.Ident (len = 1) {
-	//     57  .  }
+	//     57  .  .  0: *(obj @ 29)
-	//     58  }
+	//     58  .  }
+	//     59  }
 }
 
 // This example illustrates how to remove a variable declaration

src/go/ast/walk.go

@@ -71,7 +71,9 @@ func Walk(v Visitor, node Node) {
 			Walk(v, n.Doc)
 		}
 		walkIdentList(v, n.Names)
-		Walk(v, n.Type)
+		if n.Type != nil {
+			Walk(v, n.Type)
+		}
 		if n.Tag != nil {
 			Walk(v, n.Tag)
 		}
@@ -161,6 +163,9 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.Fields)
 
 	case *FuncType:
+		if n.TParams != nil {
+			Walk(v, n.TParams)
+		}
 		if n.Params != nil {
 			Walk(v, n.Params)
 		}
@@ -315,6 +320,9 @@ func Walk(v Visitor, node Node) {
 			Walk(v, n.Doc)
 		}
 		Walk(v, n.Name)
+		if n.TParams != nil {
+			Walk(v, n.TParams)
+		}
 		Walk(v, n.Type)
 		if n.Comment != nil {
 			Walk(v, n.Comment)