--json option for wasmtime settings command (#5411)

* - Added `--json` flag to settings command
 - Refactored gathering of data into a `Settings` struct which can be used in both human/machine readable paths
 - Split out human readable output to another function, it produces exactly the same result as before

* Outputting JSON by hand formatting it. This approach has the advantage of not needing any extra dependencies (i.e.serde), but is obviously a bit ugly.

* Rewritten JSON serialization to use serde

* Commenting and formatting

* Applied rustfmt

* Reduced version of serde and serde_json to fix cargo vet errors

* Updated cargo.lock to fix cargo vet errors

Cargo.lock

@@ -3475,6 +3475,8 @@ dependencies = [
  "once_cell",
  "rayon",
  "rustix",
+ "serde",
+ "serde_json",
  "target-lexicon",
  "tempfile",
  "test-programs",

Cargo.toml

@@ -38,6 +38,8 @@ humantime = "2.0.0"
 once_cell = { workspace = true }
 listenfd = "1.0.0"
 wat = { workspace = true }
+serde = "1.0.94"
+serde_json = "1.0.26"
 
 [target.'cfg(unix)'.dependencies]
 rustix = { workspace = true, features = ["mm", "param"] }

src/commands/settings.rs

@@ -2,9 +2,10 @@
 
 use anyhow::{anyhow, Result};
 use clap::Parser;
+use serde::{ser::SerializeMap, Serialize};
 use std::collections::BTreeMap;
 use std::str::FromStr;
-use wasmtime_environ::{FlagValue, Setting, SettingKind};
+use wasmtime_environ::{CompilerBuilder, FlagValue, Setting, SettingKind};
 
 /// Displays available Cranelift settings for a target.
 #[derive(Parser)]
@@ -13,79 +14,167 @@ pub struct SettingsCommand {
     /// The target triple to get the settings for; defaults to the host triple.
     #[clap(long, value_name = "TARGET")]
     target: Option<String>,
+
+    /// Switch output format to JSON
+    #[clap(long)]
+    json: bool,
+}
+
+struct SettingData(Setting);
+
+impl Serialize for SettingData {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        let mut map = serializer.serialize_map(None)?;
+        map.serialize_entry("name", self.0.name)?;
+        map.serialize_entry("description", self.0.description)?;
+        map.serialize_entry("values", &self.0.values)?;
+        map.end()
+    }
+}
+
+// Gather together all of the setting data to displays
+#[derive(Serialize)]
+struct Settings {
+    triple: String,
+
+    enums: Vec<SettingData>,
+    nums: Vec<SettingData>,
+    bools: Vec<SettingData>,
+    presets: Vec<SettingData>,
+
+    inferred: Option<Vec<String>>,
+}
+
+impl Settings {
+    fn from_builder(builder: &Box<dyn CompilerBuilder>) -> Settings {
+        let mut settings = Settings {
+            triple: builder.triple().to_string(),
+            enums: Vec::new(),
+            nums: Vec::new(),
+            bools: Vec::new(),
+            presets: Vec::new(),
+            inferred: None,
+        };
+        settings.add_settings(builder.settings());
+        settings
+    }
+
+    fn infer(&mut self, builder: &Box<dyn CompilerBuilder>) -> Result<()> {
+        let compiler = builder.build()?;
+        let values = compiler.isa_flags().into_iter().collect::<BTreeMap<_, _>>();
+        let mut result = Vec::new();
+        for (name, value) in values {
+            if let FlagValue::Bool(true) = value {
+                result.push(name);
+            }
+        }
+
+        self.inferred = Some(result);
+
+        Ok(())
+    }
+
+    fn add_setting(&mut self, setting: Setting) {
+        let collection = match setting.kind {
+            SettingKind::Enum => &mut self.enums,
+            SettingKind::Num => &mut self.nums,
+            SettingKind::Bool => &mut self.bools,
+            SettingKind::Preset => &mut self.presets,
+        };
+        collection.push(SettingData(setting));
+    }
+
+    fn add_settings<I>(&mut self, iterable: I)
+    where
+        I: IntoIterator<Item = Setting>,
+    {
+        for item in iterable.into_iter() {
+            self.add_setting(item);
+        }
+    }
+
+    fn is_empty(&self) -> bool {
+        self.enums.is_empty()
+            && self.nums.is_empty()
+            && self.bools.is_empty()
+            && self.presets.is_empty()
+    }
 }
 
 impl SettingsCommand {
     /// Executes the command.
     pub fn execute(self) -> Result<()> {
+        // Gather settings from the cranelift compiler builder
         let mut builder = wasmtime_cranelift::builder();
         if let Some(target) = &self.target {
             let target = target_lexicon::Triple::from_str(target).map_err(|e| anyhow!(e))?;
             builder.target(target)?;
         }
+        let mut settings = Settings::from_builder(&builder);
 
-        let mut enums = (Vec::new(), 0, "Enum settings:");
+        // Add inferred settings if no target specified
-        let mut nums = (Vec::new(), 0, "Numerical settings:");
+        if self.target.is_none() {
-        let mut bools = (Vec::new(), 0, "Boolean settings:");
+            settings.infer(&builder)?;
-        let mut presets = (Vec::new(), 0, "Presets:");
-
-        for setting in builder.settings() {
-            let (collection, max, _) = match setting.kind {
-                SettingKind::Enum => &mut enums,
-                SettingKind::Num => &mut nums,
-                SettingKind::Bool => &mut bools,
-                SettingKind::Preset => &mut presets,
-            };
-
-            if setting.name.len() > *max {
-                *max = setting.name.len();
-            }
-
-            collection.push(setting);
         }
 
-        if enums.0.is_empty() && nums.0.is_empty() && bools.0.is_empty() && presets.0.is_empty() {
+        // Print settings
-            println!("Target '{}' has no settings.", builder.triple());
+        if self.json {
+            self.print_json(settings)
+        } else {
+            self.print_human_readable(settings)
+        }
+    }
+
+    fn print_json(self, settings: Settings) -> Result<()> {
+        println!("{}", serde_json::to_string_pretty(&settings)?);
+        Ok(())
+    }
+
+    fn print_human_readable(self, settings: Settings) -> Result<()> {
+        if settings.is_empty() {
+            println!("Target '{}' has no settings.", settings.triple);
             return Ok(());
         }
 
-        println!("Cranelift settings for target '{}':", builder.triple());
+        println!("Cranelift settings for target '{}':", settings.triple);
 
-        for (collection, max, header) in &mut [enums, nums, bools, presets] {
+        Self::print_settings_human_readable("Boolean settings:", &settings.bools);
-            if collection.is_empty() {
+        Self::print_settings_human_readable("Enum settings:", &settings.enums);
-                continue;
+        Self::print_settings_human_readable("Numerical settings:", &settings.nums);
-            }
+        Self::print_settings_human_readable("Presets:", &settings.presets);
 
-            collection.sort_by_key(|k| k.name);
+        if let Some(inferred) = settings.inferred {
-            println!();
-            Self::print_settings(header, collection, *max);
-        }
-
-        if self.target.is_none() {
-            let compiler = builder.build()?;
             println!();
             println!("Settings inferred for the current host:");
 
-            let values = compiler.isa_flags().into_iter().collect::<BTreeMap<_, _>>();
+            for name in inferred {
-
+                println!("  {}", name);
-            for (name, value) in values {
-                if let FlagValue::Bool(true) = value {
-                    println!("  {}", name);
-                }
             }
         }
 
         Ok(())
     }
 
-    fn print_settings(header: &str, settings: &[Setting], width: usize) {
+    fn print_settings_human_readable(header: &str, settings: &[SettingData]) {
+        if settings.is_empty() {
+            return;
+        }
+
+        println!();
         println!("{}", header);
+
+        let width = settings.iter().map(|s| s.0.name.len()).max().unwrap_or(0);
+
         for setting in settings {
             println!(
                 "  {:width$} {}{}",
-                setting.name,
+                setting.0.name,
-                setting.description,
+                setting.0.description,
                 setting
+                    .0
                     .values
                     .map(|v| format!(" Supported values: {}.", v.join(", ")))
                     .unwrap_or("".to_string()),