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cmd/cgo: simplify and fix handling of untyped constants

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Instead of trying to guess type of constants in the AST,
which is hard, use the "var cgo%d Type = Constant"
so that typechecking is left to the Go compiler.

The previous code could still fail in some cases
for constants imported from other modules
or defined in other, non-cgo files.

Fixes #30527

Change-Id: I2120cd90e90a74b9d765eeec53f6a3d2cfc1b642
Reviewed-on: https://go-review.googlesource.com/c/go/+/164897
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Rémy Oudompheng 2019-03-01 23:12:19 +01:00 • committed by Ian Lance Taylor
parent edf8539fad
commit 711ea1e716
6 changed files with 51 additions and 68 deletions
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60
src/cmd/cgo/gcc.go
View file

@ -897,21 +897,16 @@ func (p *Package) rewriteCall(f *File, call *Call) (string, bool) {
needsUnsafe = true
}
// Explicitly convert untyped constants to the
// parameter type, to avoid a type mismatch.
if p.isConst(f, arg) {
ptype := p.rewriteUnsafe(param.Go)
// Use "var x T = ..." syntax to explicitly convert untyped
// constants to the parameter type, to avoid a type mismatch.
ptype := p.rewriteUnsafe(param.Go)
if !p.needsPointerCheck(f, param.Go, args[i]) {
if ptype != param.Go {
needsUnsafe = true
}
arg = &ast.CallExpr{
Fun: ptype,
Args: []ast.Expr{arg},
}
}
if !p.needsPointerCheck(f, param.Go, args[i]) {
fmt.Fprintf(&sb, "_cgo%d := %s; ", i, gofmtPos(arg, origArg.Pos()))
fmt.Fprintf(&sb, "var _cgo%d %s = %s; ", i,
gofmtLine(ptype), gofmtPos(arg, origArg.Pos()))
continue
}
@ -1254,47 +1249,6 @@ func (p *Package) isType(t ast.Expr) bool {
return false
}
// isConst reports whether x is an untyped constant expression.
func (p *Package) isConst(f *File, x ast.Expr) bool {
switch x := x.(type) {
case *ast.BasicLit:
return true
case *ast.SelectorExpr:
id, ok := x.X.(*ast.Ident)
if !ok || id.Name != "C" {
return false
}
name := f.Name[x.Sel.Name]
if name != nil {
return name.IsConst()
}
case *ast.Ident:
return x.Name == "nil" ||
strings.HasPrefix(x.Name, "_Ciconst_") ||
strings.HasPrefix(x.Name, "_Cfconst_") ||
strings.HasPrefix(x.Name, "_Csconst_") ||
consts[x.Name]
case *ast.UnaryExpr:
return p.isConst(f, x.X)
case *ast.BinaryExpr:
return p.isConst(f, x.X) && p.isConst(f, x.Y)
case *ast.ParenExpr:
return p.isConst(f, x.X)
case *ast.CallExpr:
// Calling the builtin function complex on two untyped
// constants returns an untyped constant.
// TODO: It's possible to construct a case that will
// erroneously succeed if there is a local function
// named "complex", shadowing the builtin, that returns
// a numeric type. I can't think of any cases that will
// erroneously fail.
if id, ok := x.Fun.(*ast.Ident); ok && id.Name == "complex" && len(x.Args) == 2 {
return p.isConst(f, x.Args[0]) && p.isConst(f, x.Args[1])
}
}
return false
}
// isVariable reports whether x is a variable, possibly with field references.
func (p *Package) isVariable(x ast.Expr) bool {
switch x := x.(type) {