Cannot link unqualified library names via Standard JSON

[cameel]

Description

In Standard JSON library addresses for linking require providing a source unit name and a library name as two separate components. For linking, these two parts are joined with a colon so even if the source unit name is empty, the colon is there.

This is different from the CLI where you can provide both L and :L in the --libraries option and for the former will let you match a reference without a colon.

I don't see a good way to support unqualified library names in the current Standard JSON structure so maybe we should just disallow unqualified library names in linkersymbol(). This would be a breaking change though.

Environment

• Compiler version: 0.8.9 (develop)

Steps to Reproduce

input.json:

{
    "language": "Yul",
    "sources": {
        "contract.sol": {"content": "{ sstore(0, linkersymbol(\"L\")) }"}
    },
    "settings": {
        "outputSelection": {"*": {"*": ["evm.bytecode"]}},
        "libraries": {
            "": {
                "L": "0x1234567890123456789012345678901234567890"
            }
        }
    }
}

solc --json-indent 4 --standard-json input.json

Output:

{
    "contracts":
    {
        "contract.sol":
        {
            "object":
            {
                "evm":
                {
                    "bytecode":
                    {
                        "functionDebugData": {},
                        "generatedSources": [],
                        "linkReferences":
                        {
                            "":
                            {
                                "L":
                                [
                                    {
                                        "length": 20,
                                        "start": 1
                                    }
                                ]
                            }
                        },
                        "object": "73__$8aa64f937099b65a4febc243a5ae0f2d64$__600055",
                        "opcodes": "PUSH20 0x0 PUSH1 0x0 SSTORE ",
                        "sourceMap": "12:17:0:-:0;9:1;2:28"
                    }
                }
            }
        }
    }
}

If you change linkersymbol("L")) in the input to linkersymbol(":L")), the unlinked reference disappears.