Stack overflow on validate_executable for fragment cycles

[gmac]

Description

The following fails with a fatal runtime error: stack overflow...

let source = r#"
   { ...fragA }
   fragment fragA on Query { ...fragA }
"#;
let mut compiler = apollo_compiler::ApolloCompiler::new();
let file_id = compiler.add_executable(source, "");
compiler.db.validate_executable(file_id);

Interestingly, this only happens when the fragment spread is the initial selection in both scopes. Either of these permutations where the spread is preceded by another selection avoids the stack overflow:

{ sfoo ...fragA }
fragment fragA on Query { ...fragA }

Or...

{ ...fragA }
fragment fragA on Query { sfoo ...fragA }

Steps to reproduce

See snippet above.

Expected result

Should get an error rather than a stack overflow.

Actual result

Stack overflow.

Environment

• Operating system and version: macos, 13.3.1
• Shell (bash/zsh/powershell): zsh
• apollo-rs crate: apollo-compiler
• Crate version: 0.8.0

[lrlna]

fixed in #544 & #552