fix: detect default comm clause in select from AST (#678)

* fix: detect default comm clause in select from AST The heuristic to distinguish a default comm clause was too weak. Make it robust by using AST. Fixes #646. * rename test to avoid conflict
traefik · Jun 10, 2020 · 82b499a · 82b499a
1 parent 0ef7f8f
commit 82b499a
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Showing 3 changed files with 113 additions and 82 deletions.
diff --git a/_test/select13.go b/_test/select13.go
@@ -0,0 +1,16 @@
+package main
+
+func main() {
+	var c interface{} = int64(1)
+	q := make(chan struct{})
+	select {
+	case q <- struct{}{}:
+		println("unexpected")
+	default:
+		_ = c.(int64)
+	}
+	println("bye")
+}
+
+// Output:
+// bye
diff --git a/interp/ast.go b/interp/ast.go
@@ -31,6 +31,7 @@ const (
 	caseClause
 	chanType
 	commClause
+	commClauseDefault
 	compositeLitExpr
 	constDecl
 	continueStmt
@@ -93,80 +94,81 @@ const (
 )
 
 var kinds = [...]string{
-	undefNode:        "undefNode",
-	addressExpr:      "addressExpr",
-	arrayType:        "arrayType",
-	assignStmt:       "assignStmt",
-	assignXStmt:      "assignXStmt",
-	basicLit:         "basicLit",
-	binaryExpr:       "binaryExpr",
-	blockStmt:        "blockStmt",
-	branchStmt:       "branchStmt",
-	breakStmt:        "breakStmt",
-	callExpr:         "callExpr",
-	caseBody:         "caseBody",
-	caseClause:       "caseClause",
-	chanType:         "chanType",
-	commClause:       "commClause",
-	compositeLitExpr: "compositeLitExpr",
-	constDecl:        "constDecl",
-	continueStmt:     "continueStmt",
-	declStmt:         "declStmt",
-	deferStmt:        "deferStmt",
-	defineStmt:       "defineStmt",
-	defineXStmt:      "defineXStmt",
-	ellipsisExpr:     "ellipsisExpr",
-	exprStmt:         "exprStmt",
-	fallthroughtStmt: "fallthroughStmt",
-	fieldExpr:        "fieldExpr",
-	fieldList:        "fieldList",
-	fileStmt:         "fileStmt",
-	forStmt0:         "forStmt0",
-	forStmt1:         "forStmt1",
-	forStmt2:         "forStmt2",
-	forStmt3:         "forStmt3",
-	forStmt3a:        "forStmt3a",
-	forStmt4:         "forStmt4",
-	forRangeStmt:     "forRangeStmt",
-	funcDecl:         "funcDecl",
-	funcType:         "funcType",
-	funcLit:          "funcLit",
-	goStmt:           "goStmt",
-	gotoStmt:         "gotoStmt",
-	identExpr:        "identExpr",
-	ifStmt0:          "ifStmt0",
-	ifStmt1:          "ifStmt1",
-	ifStmt2:          "ifStmt2",
-	ifStmt3:          "ifStmt3",
-	importDecl:       "importDecl",
-	importSpec:       "importSpec",
-	incDecStmt:       "incDecStmt",
-	indexExpr:        "indexExpr",
-	interfaceType:    "interfaceType",
-	keyValueExpr:     "keyValueExpr",
-	labeledStmt:      "labeledStmt",
-	landExpr:         "landExpr",
-	lorExpr:          "lorExpr",
-	mapType:          "mapType",
-	parenExpr:        "parenExpr",
-	rangeStmt:        "rangeStmt",
-	returnStmt:       "returnStmt",
-	selectStmt:       "selectStmt",
-	selectorExpr:     "selectorExpr",
-	selectorImport:   "selectorImport",
-	sendStmt:         "sendStmt",
-	sliceExpr:        "sliceExpr",
-	starExpr:         "starExpr",
-	structType:       "structType",
-	switchStmt:       "switchStmt",
-	switchIfStmt:     "switchIfStmt",
-	typeAssertExpr:   "typeAssertExpr",
-	typeDecl:         "typeDecl",
-	typeSpec:         "typeSpec",
-	typeSwitch:       "typeSwitch",
-	unaryExpr:        "unaryExpr",
-	valueSpec:        "valueSpec",
-	varDecl:          "varDecl",
+	undefNode:         "undefNode",
+	addressExpr:       "addressExpr",
+	arrayType:         "arrayType",
+	assignStmt:        "assignStmt",
+	assignXStmt:       "assignXStmt",
+	basicLit:          "basicLit",
+	binaryExpr:        "binaryExpr",
+	blockStmt:         "blockStmt",
+	branchStmt:        "branchStmt",
+	breakStmt:         "breakStmt",
+	callExpr:          "callExpr",
+	caseBody:          "caseBody",
+	caseClause:        "caseClause",
+	chanType:          "chanType",
+	commClause:        "commClause",
+	commClauseDefault: "commClauseDefault",
+	compositeLitExpr:  "compositeLitExpr",
+	constDecl:         "constDecl",
+	continueStmt:      "continueStmt",
+	declStmt:          "declStmt",
+	deferStmt:         "deferStmt",
+	defineStmt:        "defineStmt",
+	defineXStmt:       "defineXStmt",
+	ellipsisExpr:      "ellipsisExpr",
+	exprStmt:          "exprStmt",
+	fallthroughtStmt:  "fallthroughStmt",
+	fieldExpr:         "fieldExpr",
+	fieldList:         "fieldList",
+	fileStmt:          "fileStmt",
+	forStmt0:          "forStmt0",
+	forStmt1:          "forStmt1",
+	forStmt2:          "forStmt2",
+	forStmt3:          "forStmt3",
+	forStmt3a:         "forStmt3a",
+	forStmt4:          "forStmt4",
+	forRangeStmt:      "forRangeStmt",
+	funcDecl:          "funcDecl",
+	funcType:          "funcType",
+	funcLit:           "funcLit",
+	goStmt:            "goStmt",
+	gotoStmt:          "gotoStmt",
+	identExpr:         "identExpr",
+	ifStmt0:           "ifStmt0",
+	ifStmt1:           "ifStmt1",
+	ifStmt2:           "ifStmt2",
+	ifStmt3:           "ifStmt3",
+	importDecl:        "importDecl",
+	importSpec:        "importSpec",
+	incDecStmt:        "incDecStmt",
+	indexExpr:         "indexExpr",
+	interfaceType:     "interfaceType",
+	keyValueExpr:      "keyValueExpr",
+	labeledStmt:       "labeledStmt",
+	landExpr:          "landExpr",
+	lorExpr:           "lorExpr",
+	mapType:           "mapType",
+	parenExpr:         "parenExpr",
+	rangeStmt:         "rangeStmt",
+	returnStmt:        "returnStmt",
+	selectStmt:        "selectStmt",
+	selectorExpr:      "selectorExpr",
+	selectorImport:    "selectorImport",
+	sendStmt:          "sendStmt",
+	sliceExpr:         "sliceExpr",
+	starExpr:          "starExpr",
+	structType:        "structType",
+	switchStmt:        "switchStmt",
+	switchIfStmt:      "switchIfStmt",
+	typeAssertExpr:    "typeAssertExpr",
+	typeDecl:          "typeDecl",
+	typeSpec:          "typeSpec",
+	typeSwitch:        "typeSwitch",
+	unaryExpr:         "unaryExpr",
+	valueSpec:         "valueSpec",
+	varDecl:           "varDecl",
 }
 
 func (k nkind) String() string {
@@ -565,7 +567,11 @@ func (interp *Interpreter) ast(src, name string) (string, *node, error) {
 			st.push(addChild(&root, anc, pos, chanType, aNop), nod)
 
 		case *ast.CommClause:
-			st.push(addChild(&root, anc, pos, commClause, aNop), nod)
+			kind := commClause
+			if a.Comm == nil {
+				kind = commClauseDefault
+			}
+			st.push(addChild(&root, anc, pos, kind, aNop), nod)
 
 		case *ast.CommentGroup:
 			return false

diff --git a/interp/cfg.go b/interp/cfg.go
@@ -203,6 +203,9 @@ func (interp *Interpreter) cfg(root *node, pkgID string) ([]*node, error) {
 				nod.typ = typ
 			}
 
+		case commClauseDefault:
+			sc = sc.pushBloc()
+
 		case commClause:
 			sc = sc.pushBloc()
 			if len(n.child) > 0 && n.child[0].action == aAssign {
@@ -903,19 +906,25 @@ func (interp *Interpreter) cfg(root *node, pkgID string) ([]*node, error) {
 		case caseClause:
 			sc = sc.pop()
 
+		case commClauseDefault:
+			wireChild(n)
+			sc = sc.pop()
+			if len(n.child) == 0 {
+				return
+			}
+			n.start = n.child[0].start
+			n.lastChild().tnext = n.anc.anc // exit node is selectStmt
+
 		case commClause:
 			wireChild(n)
-			switch len(n.child) {
-			case 0:
-				sc.pop()
+			sc = sc.pop()
+			if len(n.child) == 0 {
 				return
-			case 1:
-				n.start = n.child[0].start // default clause
-			default:
+			}
+			if len(n.child) > 1 {
 				n.start = n.child[1].start // Skip chan operation, performed by select
 			}
 			n.lastChild().tnext = n.anc.anc // exit node is selectStmt
-			sc = sc.pop()
 
 		case compositeLitExpr:
 			wireChild(n)