x/tools/go/callgraph/cha: spurious callgraph edges to unexported functions

[jcd2]

When the cha library processes a method call on an interface value, it must calculate the concrete methods that it may call at runtime. It does this by finding all methods whose name matches the selector, and whose type satisfies the interface. The name matching is done using plain string equality, but this is not quite right, because unexported identifiers in different packages are always considered different, even if they are spelled the same.

Performing the string matching on the output of go/types.Id for the selector and method names would fix this.

See the test program in https://go.dev/cl/574955 for an example. There, a type S1 which embeds a types.Object, and a method order are defined:

type S1 struct {
        types.Object
        X int
}

func (s *S1) order(x int) int {
        return s.X + x
}

S1 satisfies the go/types.Object interface, but code in go/types that calls order on a types.Object value cannot call the order method of S1 defined here, it can only call an order method of the embedded types.Object which was defined in go/types.

[gopherbot]

Change https://go.dev/cl/574955 mentions this issue: go/callgraph/cha: more precise resolution of unexported methods