Add if-installed and if-not-installed helpers

Cargo.lock

@@ -596,6 +596,7 @@ dependencies = [
  "sys-info",
  "tempfile",
  "toml",
+ "which",
 ]
 
 [[package]]
@@ -604,6 +605,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "56ce8c6da7551ec6c462cbaf3bfbc75131ebbfa1c944aeaa9dab51ca1c5f0c3b"
 
+[[package]]
+name = "either"
+version = "1.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a26ae43d7bcc3b814de94796a5e736d4029efb0ee900c12e2d54c993ad1a1e07"
+
 [[package]]
 name = "encode_unicode"
 version = "0.3.6"
@@ -2957,6 +2964,19 @@ version = "0.25.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1778a42e8b3b90bff8d0f5032bf22250792889a5cdc752aa0020c84abe3aaf10"
 
+[[package]]
+name = "which"
+version = "5.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9bf3ea8596f3a0dd5980b46430f2058dfe2c36a27ccfbb1845d6fbfcd9ba6e14"
+dependencies = [
+ "either",
+ "home",
+ "once_cell",
+ "rustix",
+ "windows-sys 0.48.0",
+]
+
 [[package]]
 name = "winapi"
 version = "0.3.9"

Cargo.toml

@@ -29,6 +29,7 @@ serde_json = "1.0.111"
 sys-info = "0.9.1"
 tempfile = "3.9.0"
 toml = "0.8.8"
+which = "5.0.0"
 
 # The profile that 'cargo dist' will build with
 [profile.dist]

src/main.rs

@@ -44,7 +44,7 @@ fn init_logging(verbose: bool) {
     builder
         .filter_module("handlebars", log::LevelFilter::Error)
         .filter_module("rustls", log::LevelFilter::Error)
-        .filter_module("", log::LevelFilter::Error)
+        .filter_module("reqwest", log::LevelFilter::Error)
         .init();
 }
 

src/templating/helpers.rs

@@ -0,0 +1,44 @@
+use handlebars::{
+    Context, Handlebars, Helper, HelperDef, HelperResult, Output, RenderContext, RenderError,
+    RenderErrorReason, Renderable,
+};
+use which::which;
+
+pub struct IfInstalledHelper {
+    pub positive: bool,
+}
+
+impl HelperDef for IfInstalledHelper {
+    fn call<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'rc>,
+        r: &'reg Handlebars<'reg>,
+        ctx: &'rc Context,
+        rc: &mut RenderContext<'reg, 'rc>,
+        out: &mut dyn Output,
+    ) -> HelperResult {
+        let bin = h
+            .param(0)
+            .ok_or_else(|| RenderErrorReason::ParamNotFoundForIndex("if-installed", 0))?;
+        let bin = if bin.is_value_missing() {
+            bin.relative_path()
+                .ok_or_else(|| RenderErrorReason::ParamNotFoundForIndex("if-installed", 0))?
+                .to_owned()
+        } else {
+            bin.value().to_string()
+        };
+        log::debug!("Checking if `{bin}` is installed");
+
+        if which(&bin).is_ok() == self.positive {
+            log::debug!("`{bin}` is installed");
+            h.template()
+                .ok_or_else(|| RenderErrorReason::BlockContentRequired)?
+                .render(r, ctx, rc, out)
+                .map_err(RenderError::from)
+                .into()
+        } else {
+            log::debug!("`{bin}` is not installed");
+            HelperResult::Ok(())
+        }
+    }
+}

src/templating/mod.rs

@@ -5,6 +5,7 @@ use handlebars_switch::SwitchHelper;
 use lazy_static::lazy_static;
 use miette::{Context, IntoDiagnostic, Result};
 use serde::Serialize;
+mod helpers;
 
 pub fn render<T: Serialize>(template: &str, ctx: T) -> Result<String> {
     engine()
@@ -16,6 +17,14 @@ pub fn render<T: Serialize>(template: &str, ctx: T) -> Result<String> {
 fn engine<'a>() -> Handlebars<'a> {
     let mut hb = Handlebars::new();
     hb.register_helper("switch", Box::new(SwitchHelper));
+    hb.register_helper(
+        "if-installed",
+        Box::new(helpers::IfInstalledHelper { positive: true }),
+    );
+    hb.register_helper(
+        "if-not-installed",
+        Box::new(helpers::IfInstalledHelper { positive: false }),
+    );
     hb
 }