cgo: implement C.struct_ types

These types (called elaborated types in C) are used as part of linked
lists, among others.

This is part an extra feature (to be compatible with CGo C.struct_
types) and part a bugfix: linked lists would result in endless recursion
leading to a stack overflow.

Author: aykevl

loader/cgo.go

@@ -17,11 +17,12 @@ import (
 type fileInfo struct {
 	*ast.File
 	*Package
-	filename   string
-	functions  map[string]*functionInfo
-	globals    map[string]*globalInfo
-	typedefs   map[string]*typedefInfo
-	importCPos token.Pos
+	filename        string
+	functions       map[string]*functionInfo
+	globals         map[string]*globalInfo
+	typedefs        map[string]*typedefInfo
+	elaboratedTypes map[string]ast.Expr
+	importCPos      token.Pos
 }
 
 // functionInfo stores some information about a Cgo function found by libclang
@@ -81,12 +82,13 @@ typedef unsigned long long  _Cgo_ulonglong;
 // comment with libclang, and modifies the AST to use this information.
 func (p *Package) processCgo(filename string, f *ast.File, cflags []string) []error {
 	info := &fileInfo{
-		File:      f,
-		Package:   p,
-		filename:  filename,
-		functions: map[string]*functionInfo{},
-		globals:   map[string]*globalInfo{},
-		typedefs:  map[string]*typedefInfo{},
+		File:            f,
+		Package:         p,
+		filename:        filename,
+		functions:       map[string]*functionInfo{},
+		globals:         map[string]*globalInfo{},
+		typedefs:        map[string]*typedefInfo{},
+		elaboratedTypes: map[string]ast.Expr{},
 	}
 
 	// Find `import "C"` statements in the file.
@@ -142,9 +144,12 @@ func (p *Package) processCgo(filename string, f *ast.File, cflags []string) []er
 	// Forward C types to Go types (like C.uint32_t -> uint32).
 	info.addTypeAliases()
 
-	// Add type declarations for C types, declared using typeef in C.
+	// Add type declarations for C types, declared using typedef in C.
 	info.addTypedefs()
 
+	// Add elaborated types for C structs and unions.
+	info.addElaboratedTypes()
+
 	// Patch the AST to use the declared types and functions.
 	f = astutil.Apply(f, info.walker, nil).(*ast.File)
 
@@ -376,6 +381,42 @@ func (info *fileInfo) addTypedefs() {
 	info.Decls = append(info.Decls, gen)
 }
 
+// addElaboratedTypes adds C elaborated types as aliases. These are the "struct
+// foo" or "union foo" types, often used in a typedef.
+//
+// See also:
+// https://en.cppreference.com/w/cpp/language/elaborated_type_specifier
+func (info *fileInfo) addElaboratedTypes() {
+	gen := &ast.GenDecl{
+		TokPos: info.importCPos,
+		Tok:    token.TYPE,
+	}
+	names := make([]string, 0, len(info.elaboratedTypes))
+	for name := range info.elaboratedTypes {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	for _, name := range names {
+		typ := info.elaboratedTypes[name]
+		typeName := "C.struct_" + name
+		obj := &ast.Object{
+			Kind: ast.Typ,
+			Name: typeName,
+		}
+		typeSpec := &ast.TypeSpec{
+			Name: &ast.Ident{
+				NamePos: info.importCPos,
+				Name:    typeName,
+				Obj:     obj,
+			},
+			Type: typ,
+		}
+		obj.Decl = typeSpec
+		gen.Specs = append(gen.Specs, typeSpec)
+	}
+	info.Decls = append(info.Decls, gen)
+}
+
 // walker replaces all "C".<something> expressions to literal "C.<something>"
 // expressions. Such expressions are impossible to write in Go (a dot cannot be
 // used in the middle of a name) so in practice all C identifiers live in a

loader/libclang.go

@@ -332,7 +332,25 @@ func (info *fileInfo) makeASTType(typ C.CXType) ast.Expr {
 		}
 	case C.CXType_Elaborated:
 		underlying := C.clang_Type_getNamedType(typ)
-		return info.makeASTType(underlying)
+		switch underlying.kind {
+		case C.CXType_Record:
+			cursor := C.tinygo_clang_getTypeDeclaration(typ)
+			name := getString(C.tinygo_clang_getCursorSpelling(cursor))
+			// It is possible that this is a recursive definition, for example
+			// in linked lists (structs contain a pointer to the next element
+			// of the same type). If the name exists in info.elaboratedTypes,
+			// it is being processed, although it may not be fully defined yet.
+			if _, ok := info.elaboratedTypes[name]; !ok {
+				info.elaboratedTypes[name] = nil // predeclare (to avoid endless recursion)
+				info.elaboratedTypes[name] = info.makeASTType(underlying)
+			}
+			return &ast.Ident{
+				NamePos: info.importCPos,
+				Name:    "C.struct_" + name,
+			}
+		default:
+			panic("unknown elaborated type")
+		}
 	case C.CXType_Record:
 		cursor := C.tinygo_clang_getTypeDeclaration(typ)
 		fieldList := &ast.FieldList{

testdata/cgo/main.go

@@ -53,6 +53,14 @@ func main() {
 	C.unionSetData(5, 8, 1)
 	println("union global data:", C.globalUnion.data[0], C.globalUnion.data[1], C.globalUnion.data[2])
 	println("union field:", printUnion(C.globalUnion).f)
+
+	// recursive types, test using a linked list
+	lastElement := &C.list_t{n: 7, next: nil}
+	list := &C.list_t{n: 3, next: &C.struct_list_t{n: 6, next: (*C.struct_list_t)(lastElement)}}
+	for list != nil {
+		println("n in chain:", list.n)
+		list = (*C.list_t)(list.next)
+	}
 }
 
 func printUnion(union C.joined_t) C.joined_t {

testdata/cgo/main.h

@@ -12,6 +12,12 @@ typedef struct collection {
 	unsigned char c;
 } collection_t;
 
+// linked list
+typedef struct list_t {
+	int           n;
+	struct list_t *next;
+} list_t;
+
 typedef union joined {
 	myint s;
 	float f;

testdata/cgo/out.txt

@@ -24,3 +24,6 @@ union local data:  5 8 1
 union s method: -33 false
 union f: +6.280000e+000
 union field: +6.280000e+000
+n in chain: 3
+n in chain: 6
+n in chain: 7