cgo: add file AST for fake C file locations

This is needed for the type checker, otherwise it doesn't know which Go
version it should use for type checking.

cgo/cgo.go

@@ -25,9 +25,15 @@ import (
 	"golang.org/x/tools/go/ast/astutil"
 )
 
+// Function that's only defined in Go 1.22.
+var setASTFileFields = func(f *ast.File, start, end token.Pos) {
+}
+
 // cgoPackage holds all CGo-related information of a package.
 type cgoPackage struct {
 	generated       *ast.File
+	packageName     string
+	cgoFiles        []*ast.File
 	generatedPos    token.Pos
 	errors          []error
 	currentDir      string // current working directory
@@ -165,8 +171,9 @@ func GoBytes(ptr unsafe.Pointer, length C.int) []byte {
 // functions), the CFLAGS and LDFLAGS found in #cgo lines, and a map of file
 // hashes of the accessed C header files. If there is one or more error, it
 // returns these in the []error slice but still modifies the AST.
-func Process(files []*ast.File, dir, importPath string, fset *token.FileSet, cflags []string) (*ast.File, []string, []string, []string, map[string][]byte, []error) {
+func Process(files []*ast.File, dir, importPath string, fset *token.FileSet, cflags []string) ([]*ast.File, []string, []string, []string, map[string][]byte, []error) {
 	p := &cgoPackage{
+		packageName:     files[0].Name.Name,
 		currentDir:      dir,
 		importPath:      importPath,
 		fset:            fset,
@@ -202,6 +209,7 @@ func Process(files []*ast.File, dir, importPath string, fset *token.FileSet, cfl
 		// This is always a bug in the cgo package.
 		panic("unexpected error: " + err.Error())
 	}
+	p.cgoFiles = append(p.cgoFiles, p.generated)
 	// If the Comments field is not set to nil, the go/format package will get
 	// confused about where comments should go.
 	p.generated.Comments = nil
@@ -332,7 +340,7 @@ func Process(files []*ast.File, dir, importPath string, fset *token.FileSet, cfl
 	// Print the newly generated in-memory AST, for debugging.
 	//ast.Print(fset, p.generated)
 
-	return p.generated, p.cgoHeaders, p.cflags, p.ldflags, p.visitedFiles, p.errors
+	return p.cgoFiles, p.cgoHeaders, p.cflags, p.ldflags, p.visitedFiles, p.errors
 }
 
 func (p *cgoPackage) newCGoFile(file *ast.File, index int) *cgoFile {

cgo/cgo_go122.go

@@ -0,0 +1,17 @@
+//go:build go1.22
+
+package cgo
+
+// Code specifically for Go 1.22.
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+func init() {
+	setASTFileFields = func(f *ast.File, start, end token.Pos) {
+		f.FileStart = start
+		f.FileEnd = end
+	}
+}

cgo/cgo_test.go

@@ -55,7 +55,7 @@ func TestCGo(t *testing.T) {
 			}
 
 			// Process the AST with CGo.
-			cgoAST, _, _, _, _, cgoErrors := Process([]*ast.File{f}, "testdata", "main", fset, cflags)
+			cgoFiles, _, _, _, _, cgoErrors := Process([]*ast.File{f}, "testdata", "main", fset, cflags)
 
 			// Check the AST for type errors.
 			var typecheckErrors []error
@@ -66,7 +66,7 @@ func TestCGo(t *testing.T) {
 				Importer: simpleImporter{},
 				Sizes:    types.SizesFor("gccgo", "arm"),
 			}
-			_, err = config.Check("", fset, []*ast.File{f, cgoAST}, nil)
+			_, err = config.Check("", fset, append([]*ast.File{f}, cgoFiles...), nil)
 			if err != nil && len(typecheckErrors) == 0 {
 				// Only report errors when no type errors are found (an
 				// unexpected condition).
@@ -91,7 +91,7 @@ func TestCGo(t *testing.T) {
 				}
 				buf.WriteString("\n")
 			}
-			err = format.Node(buf, fset, cgoAST)
+			err = format.Node(buf, fset, cgoFiles[0])
 			if err != nil {
 				t.Errorf("could not write out CGo AST: %v", err)
 			}

cgo/libclang.go

@@ -589,6 +589,13 @@ func (p *cgoPackage) getClangLocationPosition(location C.CXSourceLocation, tu C.
 		f := p.fset.AddFile(filename, -1, int(size))
 		f.SetLines(lines)
 		p.tokenFiles[filename] = f
+		// Add dummy file AST, to satisfy the type checker.
+		astFile := &ast.File{
+			Package: f.Pos(0),
+			Name:    ast.NewIdent(p.packageName),
+		}
+		setASTFileFields(astFile, f.Pos(0), f.Pos(int(size)))
+		p.cgoFiles = append(p.cgoFiles, astFile)
 	}
 	positionFile := p.tokenFiles[filename]
 

loader/loader.go

@@ -447,7 +447,7 @@ func (p *Package) parseFiles() ([]*ast.File, error) {
 		if errs != nil {
 			fileErrs = append(fileErrs, errs...)
 		}
-		files = append(files, generated)
+		files = append(files, generated...)
 		p.program.LDFlags = append(p.program.LDFlags, ldflags...)
 	}