Improve compilation time in standard JSON mode and honor requested output (#461)

# Description

Compilation times for resolc were significantly slower than solc when:
* Multiple files were included in the JSON input file via
`--standard-json`
* And none of the files requested code generation
* (If only a subset of files requested code generation, both resolc and
solc were very slow)

Reason:
* Resolc unconditionally generated bytecode for all contracts, even if
not requested.
* When compiling to PolkaVM bytecode, we need to pass additional flags
(e.g. `irOptimized`) to solc. If these flags were not explicitly
requested, resolc also added these to the requested output since PolkaVM
bytecode was always generated.

## Breaking Changes

The following changes are breaking, but fix the semantics to match its
intended behavior:

* Compiling with `--standard-json` now compiles to PolkaVM bytecode
***only*** for the contracts explicitly requested in the
`outputSelection`.
* Compiling with `--standard-json` now outputs ***only*** the explicitly
requested output (e.g. `evm.assembly`, `evm.bytecode`, `ast`, etc.).

```jsonc
// Example:
{
  "settings": {
    // ...
    "outputSelection": {
      "src/common/GasService.sol": {
        // Contracts in this file will generate bytecode.
        // Only these fields of the JSON output selection will be in the `contracts` output.
        "*": ["abi", "evm.methodIdentifiers", "metadata", "evm.bytecode"],
        // Only this field of the JSON output selection will be in the `sources` output.
        "": ["ast"]
      },
      "src/common/Gateway.sol": {
        // No contracts in this file will generate bytecode.
        "*": ["abi", "evm.methodIdentifiers", "metadata"],
        // No `ast` will be in the `sources` output (only the automatically added `id`,
        // similar to solc as this is not a configurable output selection).
        "": []
      },
    }
  }
}
```

## Performance Improvements

When e.g. the standard JSON input file includes multiple files and
requests output for every contract as per this setting:

```jsonc
{
  "settings": {
    // ...
    "optimizer": { "enabled": true, "runs": 1 },
    "viaIR": true,
    "outputSelection": {
      "src/common/GasService.sol": {
        "*": ["abi", "evm.methodIdentifiers", "metadata", "evm.bytecode"],
      },
      // Rest of files..
    }
  }
}
```

The differences in compilation times depending on whether `evm.bytecode`
is selected in every file, one file, or no files can be seen below:

| Solc Optimizer (runs=1) | ViaIR | Request `abi`,
`evm.methodIdentifiers`, `metadata` | Request `evm.bytecode` | resolc
before | resolc after | solc v0.8.33 |

|:-----------------------:|:-----:|:---------:|:---------:|:-------------:|:------------:|:----------:|
| ✅ | ✅ | All files | All files | `~14.5s` | `~14.5s` | `~13.5s` |
| ✅ | ✅ | All files | One file | `~14.5s` | `~450ms` | `~13.5s` |
| ✅ | ✅ | All files | No files | `~14.5s` | `~390ms` | `~350ms` |

**Observations:**

* `resolc before` is roughly the same no matter the request
  * This is due to unconditionally generating bytecode
* When not requesting bytecode for any contracts:
  * `resolc after` now compiles in ~390ms (vs ~14.5s), similar to `solc`
* Neither `solc` nor `resolc after` generates bytecode when none of the
contracts request it
* When requesting bytecode for all contracts in _only one_ file:
  * `resolc after` now compiles in ~450ms (vs ~14.5s)
* `solc` still compiles in the same time as when requesting bytecode for
all contracts in all files
* This is something they have tried to improve (see
[Solidity#15373](https://github.com/argotorg/solidity/issues/15373) and
[Solidity#15615](https://github.com/argotorg/solidity/issues/15615)),
and the intended behavior seems to now be that bytecode should only be
generated when explicitly requested for each contract.
* Even though PRs have merged to try to fix it, their issue seems to
persist as of v0.8.33.

# Open Questions

* Foundry:
  * [x] Pruning of the AST:
* Just saw [this past
commit](https://github.com/paritytech/revive/pull/385) to not prune the
AST for Foundry compatibility.
    * Can Foundry not explicitly request `"": "ast"`?
    * **Answer:**
* Pruning the AST when not requested should be fine, as long as Foundry
explicitly requests it when needed.
      * Will be tested by Foundry maintainer.

# Review Notes

Changes in `docs/` (~25 files) can be skipped as they are automatically
updated after adding content to `book/` and rebuilding it.

# Resolved Issues

Closes #326

---------

Co-authored-by: xermicus <cyrill@parity.io>

crates/solc-json-interface/src/standard_json/output/mod.rs

@@ -63,7 +63,10 @@ impl Output {
                     path.to_owned(),
                     Source {
                         id: index,
-                        ast: source.content().map(|x| serde_json::to_value(x).unwrap()),
+                        ast: source
+                            .content()
+                            .map(|x| serde_json::to_value(x).unwrap())
+                            .unwrap_or_default(),
                     },
                 )
             })
@@ -100,26 +103,20 @@ impl Output {
         mut self,
         selection_to_prune: SolcStandardJsonInputSettingsSelection,
     ) -> ! {
+        for (path, source) in self.sources.iter_mut() {
+            if selection_to_prune.contains(
+                path,
+                crate::SolcStandardJsonInputSettingsSelectionFileFlag::AST,
+            ) {
+                source.ast = Default::default();
+            }
+        }
+
         for (path, contracts) in self.contracts.iter_mut() {
             for contract in contracts.values_mut() {
-                if selection_to_prune.contains(
-                    path,
-                    &crate::SolcStandardJsonInputSettingsSelectionFileFlag::Metadata,
-                ) {
-                    contract.metadata = serde_json::Value::Null;
-                }
-                if selection_to_prune.contains(
-                    path,
-                    &crate::SolcStandardJsonInputSettingsSelectionFileFlag::Yul,
-                ) {
-                    contract.ir_optimized = String::new();
-                }
-                if let Some(ref mut evm) = contract.evm {
-                    if selection_to_prune.contains(
-                        path,
-                        &crate::SolcStandardJsonInputSettingsSelectionFileFlag::MethodIdentifiers,
-                    ) {
-                        evm.method_identifiers.clear();
+                for &flag in crate::SolcStandardJsonInputSettingsSelectionFileFlag::all() {
+                    if selection_to_prune.contains(path, flag) {
+                        contract.reset_field_by_flag(flag);
                     }
                 }
             }
@@ -153,11 +150,7 @@ impl Output {
 
         let messages: Vec<SolcStandardJsonOutputError> = iter
             .flat_map(|(_path, source)| {
-                source
-                    .ast
-                    .as_ref()
-                    .map(|ast| Source::get_messages(ast, &id_paths, sources, suppressed_warnings))
-                    .unwrap_or_default()
+                Source::get_messages(&source.ast, &id_paths, sources, suppressed_warnings)
             })
             .collect();
         self.errors.extend(messages);