Implement optional initial value for pollvars (#272)

* Implement optional initial value for pollvars

* Updated docs to include the atribute initial for pollvars

crates/eww/src/app.rs

@@ -274,7 +274,6 @@ impl App {
         // refresh script-var poll stuff
         self.script_var_handler.stop_all();
 
-
         log::trace!("loading config: {:#?}", config);
 
         self.eww_config = config;

crates/eww/src/config/inbuilt.rs

@@ -13,6 +13,7 @@ macro_rules! builtin_vars {
             VarName::from($name) => ScriptVarDefinition::Poll(PollScriptVar {
                 name: VarName::from($name),
                 command: VarSource::Function($fun),
+                initial_value: None,
                 interval: $interval,
                 name_span: eww_shared_util::span::Span::DUMMY,
             })

crates/eww/src/config/script_var.rs

@@ -22,14 +22,18 @@ pub fn create_script_var_failed_warn(span: Span, var_name: &VarName, error_outpu
 
 pub fn initial_value(var: &ScriptVarDefinition) -> Result<DynVal> {
     match var {
-        ScriptVarDefinition::Poll(x) => match &x.command {
+        ScriptVarDefinition::Poll(x) => match &x.initial_value {
-            VarSource::Function(f) => {
+            Some(value) => Ok(value.clone()),
-                f().map_err(|err| anyhow!(err)).with_context(|| format!("Failed to compute initial value for {}", &var.name()))
+            None => match &x.command {
-            }
+                VarSource::Function(f) => f()
+                    .map_err(|err| anyhow!(err))
+                    .with_context(|| format!("Failed to compute initial value for {}", &var.name())),
                 VarSource::Shell(span, command) => {
                     run_command(command).map_err(|e| anyhow!(create_script_var_failed_warn(*span, var.name(), &e.to_string())))
                 }
             },
+        },
+
         ScriptVarDefinition::Listen(var) => Ok(var.initial_value.clone()),
     }
 }

crates/yuck/src/config/script_var_definition.rs

@@ -56,6 +56,7 @@ pub enum VarSource {
 pub struct PollScriptVar {
     pub name: VarName,
     pub command: VarSource,
+    pub initial_value: Option<DynVal>,
     pub interval: std::time::Duration,
     pub name_span: Span,
 }
@@ -67,6 +68,7 @@ impl FromAstElementContent for PollScriptVar {
         let result: AstResult<_> = try {
             let (name_span, name) = iter.expect_symbol()?;
             let mut attrs = iter.expect_key_values()?;
+            let initial_value = Some(attrs.primitive_optional("initial")?.unwrap_or_else(|| DynVal::from_string(String::new())));
             let interval = attrs.primitive_required::<DynVal, _>("interval")?.as_duration()?;
             let timeout = attrs
                 .primitive_optional::<DynVal, _>("timeout")?
@@ -75,7 +77,13 @@ impl FromAstElementContent for PollScriptVar {
                 .unwrap_or_else(|| std::time::Duration::from_millis(200));
             let (script_span, script) = iter.expect_literal()?;
             iter.expect_done()?;
-            Self { name_span, name: VarName(name), command: VarSource::Shell(script_span, script.to_string()), interval }
+            Self {
+                name_span,
+                name: VarName(name),
+                command: VarSource::Shell(script_span, script.to_string()),
+                initial_value,
+                interval,
+            }
         };
         result.note(r#"Expected format: `(defpoll name :interval "10s" "echo 'a shell script'")`"#)
     }

docs/src/configuration.md

@@ -1,7 +1,6 @@
 # Writing your eww configuration
 
 (For a list of all built in widgets (i.e. `box`, `label`, `button`)  see [Widget Documentation](widgets.md))
-
 Eww is configured using its own language called `yuck`.
 using yuck, you declare the structure and content of your widgets, the geometry, position and behavior of any windows,
 as well as any state and data that will be used in your widgets.
@@ -157,6 +156,7 @@ They may also be useful to have buttons within eww change what is shown within y
 ```lisp
 (defpoll time :interval "1s"
               :timeout "0.1s" ; setting timeout is optional
+              :initial "initial-value" ; setting timeout is optional
   `date +%H:%M:%S`)
 ```
 
@@ -169,6 +169,9 @@ and thus are the perfect choice for showing your time, date, as well as other bi
 Optionally, you can specify a timeout, after which the provided script will be aborted.
 This helps to avoid accidentally launching thousands of never-ending processes on your system.
 
+You can also specify an initial-value, this should prevent eww from waiting for the result of a give command during startup, thus,
+making the startup time faster.
+
 **Listening variables (`deflisten`)**
 
 ```lisp