internal/refactor/inline: reject attempts to inline in cgo code

Plus a test.

Change-Id: I2d5542ed2c6e0cabae740279d09ceaf0d22b8710
Reviewed-on: https://go-review.googlesource.com/c/tools/+/529877
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

Author: adonovan

internal/refactor/inline/callee.go

@@ -14,6 +14,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"strings"
 
 	"golang.org/x/tools/go/ast/astutil"
 	"golang.org/x/tools/go/types/typeutil"
@@ -322,6 +323,17 @@ func AnalyzeCallee(logf func(string, ...any), fset *token.FileSet, pkg *types.Pa
 		return true
 	})
 
+	// Reject attempts to inline cgo-generated functions.
+	for _, obj := range freeObjs {
+		// There are others (iconst fconst sconst fpvar macro)
+		// but this is probably sufficient.
+		if strings.HasPrefix(obj.Name, "_Cfunc_") ||
+			strings.HasPrefix(obj.Name, "_Ctype_") ||
+			strings.HasPrefix(obj.Name, "_Cvar_") {
+			return nil, fmt.Errorf("cannot inline cgo-generated functions")
+		}
+	}
+
 	// Compact content to just the FuncDecl.
 	//
 	// As a space optimization, we don't retain the complete

internal/refactor/inline/inline.go

@@ -57,6 +57,11 @@ func Inline(logf func(string, ...any), caller *Caller, callee *Callee) ([]byte,
 		return nil, fmt.Errorf("internal error: caller syntax positions are inconsistent with file content (did you forget to use FileSet.PositionFor when computing the file name?)")
 	}
 
+	// TODO(adonovan): use go1.21's ast.IsGenerated.
+	if bytes.Contains(caller.Content, []byte("// Code generated by cmd/cgo; DO NOT EDIT.")) {
+		return nil, fmt.Errorf("cannot inline calls from files that import \"C\"")
+	}
+
 	res, err := inline(logf, caller, &callee.impl)
 	if err != nil {
 		return nil, err

internal/refactor/inline/testdata/cgo.txtar

@@ -0,0 +1,45 @@
+Test that attempts to inline with caller or callee in a cgo-generated
+file are rejected.
+
+-- go.mod --
+module testdata
+go 1.12
+
+-- a/a.go --
+package a
+
+/*
+static void f() {}
+*/
+import "C"
+
+func a() {
+	C.f() //@ inline(re"f", re"cannot inline cgo-generated functions")
+	g()   //@ inline(re"g", re`cannot inline calls from files that import "C"`)
+}
+
+func g() {
+	println()
+}
+
+-- a/a2.go --
+package a
+
+func b() {
+	a() //@ inline(re"a", re"cannot inline cgo-generated functions")
+}
+
+func c() {
+	b() //@ inline(re"b", result)
+}
+
+-- result --
+package a
+
+func b() {
+	a() //@ inline(re"a", re"cannot inline cgo-generated functions")
+}
+
+func c() {
+	a() //@ inline(re"b", result)
+}