refactor/eg: fix crash while unifying wildcard with KeyValueExpr, which has no type

+ tests.

Fixes issue golang/go#10923

Change-Id: I0813cdfbb447bbd9f579bb1998b355a3179a7e79
Reviewed-on: https://go-review.googlesource.com/10332
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

refactor/eg/eg.go

@@ -84,6 +84,9 @@ a wildcard may have any integer type, for example.
 It is not possible to replace an expression by one of a different
 type, even in contexts where this is legal, such as x in fmt.Print(x).
 
+The struct literals T{x} and T{K: x} cannot both be matched by a single
+template.
+
 
 SAFETY
 

refactor/eg/eg_test.go

@@ -64,6 +64,12 @@ func Test(t *testing.T) {
 		"testdata/F.template",
 		"testdata/F1.go",
 
+		"testdata/G.template",
+		"testdata/G1.go",
+
+		"testdata/H.template",
+		"testdata/H1.go",
+
 		"testdata/bad_type.template",
 		"testdata/no_before.template",
 		"testdata/no_after_return.template",

refactor/eg/match.go

@@ -185,7 +185,17 @@ func (tr *Transformer) matchWildcard(xobj *types.Var, y ast.Expr) bool {
 	}
 
 	// Check that y is assignable to the declared type of the param.
-	if yt := tr.info.TypeOf(y); !types.AssignableTo(yt, xobj.Type()) {
+	yt := tr.info.TypeOf(y)
+	if yt == nil {
+		// y has no type.
+		// Perhaps it is an *ast.Ellipsis in [...]T{}, or
+		// an *ast.KeyValueExpr in T{k: v}.
+		// Clearly these pseudo-expressions cannot match a
+		// wildcard, but it would nice if we had a way to ignore
+		// the difference between T{v} and T{k:v} for structs.
+		return false
+	}
+	if !types.AssignableTo(yt, xobj.Type()) {
 		if tr.verbose {
 			fmt.Fprintf(os.Stderr, "%s not assignable to %s\n", yt, xobj.Type())
 		}

refactor/eg/testdata/G.template

@@ -0,0 +1,10 @@
+package templates
+
+import (
+	"go/ast" // defines many unencapsulated structs
+	"go/token"
+)
+
+func before(from, to token.Pos) ast.BadExpr { return ast.BadExpr{From: from, To: to} }
+func after(from, to token.Pos) ast.BadExpr  { return ast.BadExpr{from, to} }
+     

refactor/eg/testdata/G1.go

@@ -0,0 +1,12 @@
+// +build ignore
+
+package G1
+
+import "go/ast"
+
+func example() {
+	_ = ast.BadExpr{From: 123, To: 456} // match
+	_ = ast.BadExpr{123, 456}           // no match
+	_ = ast.BadExpr{From: 123}          // no match
+	_ = ast.BadExpr{To: 456}            // no match
+}

refactor/eg/testdata/G1.golden

@@ -0,0 +1,12 @@
+// +build ignore
+
+package G1
+
+import "go/ast"
+
+func example() {
+	_ = ast.BadExpr{123, 456}  // match
+	_ = ast.BadExpr{123, 456}  // no match
+	_ = ast.BadExpr{From: 123} // no match
+	_ = ast.BadExpr{To: 456}   // no match
+}

refactor/eg/testdata/H.template

@@ -0,0 +1,9 @@
+package templates
+
+import (
+	"go/ast" // defines many unencapsulated structs
+	"go/token"
+)
+
+func before(from, to token.Pos) ast.BadExpr { return ast.BadExpr{from, to} }
+func after(from, to token.Pos) ast.BadExpr  { return ast.BadExpr{From: from, To: to} }

refactor/eg/testdata/H1.go

@@ -0,0 +1,12 @@
+// +build ignore
+
+package H1
+
+import "go/ast"
+
+func example() {
+	_ = ast.BadExpr{From: 123, To: 456} // no match
+	_ = ast.BadExpr{123, 456}           // match
+	_ = ast.BadExpr{From: 123}          // no match
+	_ = ast.BadExpr{To: 456}            // no match
+}

refactor/eg/testdata/H1.golden

@@ -0,0 +1,12 @@
+// +build ignore
+
+package H1
+
+import "go/ast"
+
+func example() {
+	_ = ast.BadExpr{From: 123, To: 456} // no match
+	_ = ast.BadExpr{From: 123, To: 456} // match
+	_ = ast.BadExpr{From: 123}          // no match
+	_ = ast.BadExpr{To: 456}            // no match
+}