Implement loop widget (#350)

crates/eww/src/widgets/build_widget.rs

@@ -1,16 +1,20 @@
 use anyhow::{Context, Result};
 use codespan_reporting::diagnostic::Severity;
-use eww_shared_util::AttrName;
+use eww_shared_util::{AttrName, Spanned};
 use gdk::prelude::Cast;
 use gtk::{
     prelude::{BoxExt, ContainerExt, WidgetExt, WidgetExtManual},
     Orientation,
 };
 use itertools::Itertools;
-use simplexpr::SimplExpr;
-use std::{collections::HashMap, rc::Rc};
+use maplit::hashmap;
+use simplexpr::{dynval::DynVal, SimplExpr};
+use std::{cell::RefCell, collections::HashMap, rc::Rc};
 use yuck::{
-    config::{widget_definition::WidgetDefinition, widget_use::WidgetUse},
+    config::{
+        widget_definition::WidgetDefinition,
+        widget_use::{BasicWidgetUse, ChildrenWidgetUse, LoopWidgetUse, WidgetUse},
+    },
     gen_diagnostic,
 };
 
@@ -28,7 +32,7 @@ use super::widget_definitions::{resolve_orientable_attrs, resolve_range_attrs, r
 
 pub struct BuilderArgs<'a> {
     pub calling_scope: ScopeIndex,
-    pub widget_use: WidgetUse,
+    pub widget_use: BasicWidgetUse,
     pub scope_graph: &'a mut ScopeGraph,
     pub unhandled_attrs: Vec<AttrName>,
     pub widget_defs: Rc<HashMap<String, WidgetDefinition>>,
@@ -45,7 +49,26 @@ pub fn build_gtk_widget(
     graph: &mut ScopeGraph,
     widget_defs: Rc<HashMap<String, WidgetDefinition>>,
     calling_scope: ScopeIndex,
-    mut widget_use: WidgetUse,
+    widget_use: WidgetUse,
+    custom_widget_invocation: Option<Rc<CustomWidgetInvocation>>,
+) -> Result<gtk::Widget> {
+    match widget_use {
+        WidgetUse::Basic(widget_use) => {
+            build_basic_gtk_widget(graph, widget_defs, calling_scope, widget_use, custom_widget_invocation)
+        }
+        WidgetUse::Loop(_) | WidgetUse::Children(_) => Err(anyhow::anyhow!(DiagError::new(gen_diagnostic! {
+            msg = "This widget can only be used as a child of some container widget such as box",
+            label = widget_use.span(),
+            note = "Hint: try wrapping this in a `box`"
+        }))),
+    }
+}
+
+fn build_basic_gtk_widget(
+    graph: &mut ScopeGraph,
+    widget_defs: Rc<HashMap<String, WidgetDefinition>>,
+    calling_scope: ScopeIndex,
+    mut widget_use: BasicWidgetUse,
     custom_widget_invocation: Option<Rc<CustomWidgetInvocation>>,
 ) -> Result<gtk::Widget> {
     if let Some(custom_widget) = widget_defs.clone().get(&widget_use.name) {
@@ -100,7 +123,7 @@ fn build_builtin_gtk_widget(
     graph: &mut ScopeGraph,
     widget_defs: Rc<HashMap<String, WidgetDefinition>>,
     calling_scope: ScopeIndex,
-    widget_use: WidgetUse,
+    widget_use: BasicWidgetUse,
     custom_widget_invocation: Option<Rc<CustomWidgetInvocation>>,
 ) -> Result<gtk::Widget> {
     let mut bargs = BuilderArgs {
@@ -160,25 +183,93 @@ fn populate_widget_children(
     custom_widget_invocation: Option<Rc<CustomWidgetInvocation>>,
 ) -> Result<()> {
     for child in widget_use_children {
-        if child.name == "children" {
-            let custom_widget_invocation = custom_widget_invocation.clone().context("Not in a custom widget invocation")?;
+        match child {
+            WidgetUse::Children(child) => {
                 build_children_special_widget(
                     tree,
                     widget_defs.clone(),
                     calling_scope,
                     child,
                     gtk_container,
-                custom_widget_invocation,
+                    custom_widget_invocation.clone().context("Not in a custom widget invocation")?,
                 )?;
-        } else {
+            }
+            WidgetUse::Loop(child) => {
+                build_loop_special_widget(
+                    tree,
+                    widget_defs.clone(),
+                    calling_scope,
+                    child,
+                    gtk_container,
+                    custom_widget_invocation.clone(),
+                )?;
+            }
+            _ => {
                 let child_widget =
                     build_gtk_widget(tree, widget_defs.clone(), calling_scope, child, custom_widget_invocation.clone())?;
                 gtk_container.add(&child_widget);
             }
         }
+    }
     Ok(())
 }
 
+fn build_loop_special_widget(
+    tree: &mut ScopeGraph,
+    widget_defs: Rc<HashMap<String, WidgetDefinition>>,
+    calling_scope: ScopeIndex,
+    widget_use: LoopWidgetUse,
+    gtk_container: &gtk::Container,
+    custom_widget_invocation: Option<Rc<CustomWidgetInvocation>>,
+) -> Result<()> {
+    tree.register_listener(
+        calling_scope,
+        Listener {
+            needed_variables: widget_use.elements_expr.collect_var_refs(),
+            f: Box::new({
+                let custom_widget_invocation = custom_widget_invocation.clone();
+                let widget_defs = widget_defs.clone();
+                let elements_expr = widget_use.elements_expr.clone();
+                let elements_expr_span = widget_use.elements_expr_span.clone();
+                let element_name = widget_use.element_name.clone();
+                let body: WidgetUse = widget_use.body.as_ref().clone();
+                let created_children = Rc::new(RefCell::new(Vec::<gtk::Widget>::new()));
+                let gtk_container = gtk_container.clone();
+                move |tree, values| {
+                    let elements_value = elements_expr
+                        .eval(&values)?
+                        .as_json_value()?
+                        .as_array()
+                        .context("Not an array value")?
+                        .into_iter()
+                        .map(DynVal::from)
+                        .collect_vec();
+                    let mut created_children = created_children.borrow_mut();
+                    for old_child in created_children.drain(..) {
+                        unsafe { old_child.destroy() };
+                    }
+                    for element in elements_value {
+                        let scope = tree.register_new_scope(
+                            format!("for {} = {}", element_name.0, element),
+                            Some(calling_scope),
+                            calling_scope,
+                            hashmap! {
+                                element_name.clone().into() => SimplExpr::Literal(DynVal(element.0, elements_expr_span))
+                            },
+                        )?;
+                        let new_child_widget =
+                            build_gtk_widget(tree, widget_defs.clone(), scope, body.clone(), custom_widget_invocation.clone())?;
+                        gtk_container.add(&new_child_widget);
+                        created_children.push(new_child_widget);
+                    }
+
+                    Ok(())
+                }
+            }),
+        },
+    )
+}
+
 /// Handle an invocation of the special `children` [`WidgetUse`].
 /// This widget expands to multiple other widgets, thus we require the `gtk_container` we should expand the widgets into.
 /// The `custom_widget_invocation` will be used here to evaluate the provided children in their
@@ -187,13 +278,12 @@ fn build_children_special_widget(
     tree: &mut ScopeGraph,
     widget_defs: Rc<HashMap<String, WidgetDefinition>>,
     calling_scope: ScopeIndex,
-    mut widget_use: WidgetUse,
+    widget_use: ChildrenWidgetUse,
     gtk_container: &gtk::Container,
     custom_widget_invocation: Rc<CustomWidgetInvocation>,
 ) -> Result<()> {
-    assert_eq!(&widget_use.name, "children");
-
-    if let Some(nth) = widget_use.attrs.ast_optional::<SimplExpr>("nth")? {
+    if let Some(nth) = widget_use.nth_expr {
+        // TODORW this might not be necessary, if I can keep a copy of the widget I can destroy it directly, no need to go through the container.
         // This should be a custom gtk::Bin subclass,..
         let child_container = gtk::Box::new(Orientation::Horizontal, 0);
         child_container.set_homogeneous(true);
@@ -250,7 +340,7 @@ pub struct CustomWidgetInvocation {
 }
 
 /// Make sure that [`gtk::Bin`] widgets only get a single child.
-fn validate_container_children_count(container: &gtk::Container, widget_use: &WidgetUse) -> Result<(), DiagError> {
+fn validate_container_children_count(container: &gtk::Container, widget_use: &BasicWidgetUse) -> Result<(), DiagError> {
     if container.dynamic_cast_ref::<gtk::Bin>().is_some() && widget_use.children.len() > 1 {
         Err(DiagError::new(gen_diagnostic! {
             kind =  Severity::Error,

crates/simplexpr/src/dynval.rs

@@ -185,6 +185,7 @@ impl DynVal {
         }
     }
 
+    // TODO this should return Result<Vec<DynVal>> and use json parsing
     pub fn as_vec(&self) -> Result<Vec<String>> {
         if self.0.is_empty() {
             Ok(Vec::new())

crates/yuck/src/config/validate.rs

@@ -7,7 +7,11 @@ use crate::{
     parser::{ast::Ast, ast_iterator::AstIterator, from_ast::FromAst},
 };
 
-use super::{widget_definition::WidgetDefinition, widget_use::WidgetUse, Config};
+use super::{
+    widget_definition::WidgetDefinition,
+    widget_use::{BasicWidgetUse, WidgetUse},
+    Config,
+};
 use eww_shared_util::{AttrName, Span, Spanned, VarName};
 
 #[derive(Debug, thiserror::Error)]
@@ -71,6 +75,7 @@ pub fn validate_variables_in_widget_use(
     widget: &WidgetUse,
     is_in_definition: bool,
 ) -> Result<(), ValidationError> {
+    if let WidgetUse::Basic(widget) = widget {
         let matching_definition = defs.get(&widget.name);
         if let Some(matching_def) = matching_definition {
             let missing_arg = matching_def
@@ -86,7 +91,6 @@ pub fn validate_variables_in_widget_use(
                 });
             }
         }
-
         let values = widget.attrs.attrs.values();
         let unknown_var = values.filter_map(|value| value.value.as_simplexpr().ok()).find_map(|expr: SimplExpr| {
             let span = expr.span();
@@ -103,6 +107,21 @@ pub fn validate_variables_in_widget_use(
         for child in widget.children.iter() {
             let _ = validate_variables_in_widget_use(defs, variables, child, is_in_definition)?;
         }
+    } else if let WidgetUse::Loop(widget) = widget {
+        let unknown_var = widget
+            .elements_expr
+            .var_refs_with_span()
+            .iter()
+            .cloned()
+            .map(|(span, var_ref)| (span, var_ref.clone()))
+            .find(|(_, var_ref)| var_ref != &widget.element_name && !variables.contains(var_ref));
+        if let Some((span, var)) = unknown_var {
+            return Err(ValidationError::UnknownVariable { span, name: var, in_definition: is_in_definition });
+        }
+        let mut variables = variables.clone();
+        variables.insert(widget.element_name.clone());
+        let _ = validate_variables_in_widget_use(defs, &variables, &widget.body, is_in_definition)?;
+    }
 
     Ok(())
 }

crates/yuck/src/config/widget_use.rs

@@ -4,15 +4,41 @@ use simplexpr::SimplExpr;
 
 use crate::{
     config::attributes::AttrEntry,
-    error::{AstError, AstResult},
-    parser::{ast::Ast, ast_iterator::AstIterator, from_ast::FromAst},
+    error::{AstError, AstResult, AstResultExt, FormFormatError},
+    parser::{
+        ast::Ast,
+        ast_iterator::AstIterator,
+        from_ast::{FromAst, FromAstElementContent},
+    },
 };
 use eww_shared_util::{AttrName, Span, Spanned, VarName};
 
 use super::attributes::Attributes;
 
 #[derive(Debug, PartialEq, Eq, Clone, serde::Serialize)]
-pub struct WidgetUse {
+pub enum WidgetUse {
+    Basic(BasicWidgetUse),
+    Loop(LoopWidgetUse),
+    Children(ChildrenWidgetUse),
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, serde::Serialize)]
+pub struct LoopWidgetUse {
+    pub element_name: VarName,
+    pub elements_expr: SimplExpr,
+    pub elements_expr_span: Span,
+    pub body: Box<WidgetUse>,
+    pub span: Span,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, serde::Serialize)]
+pub struct ChildrenWidgetUse {
+    pub span: Span,
+    pub nth_expr: Option<SimplExpr>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, serde::Serialize)]
+pub struct BasicWidgetUse {
     pub name: String,
     pub attrs: Attributes,
     pub children: Vec<WidgetUse>,
@@ -20,39 +46,79 @@ pub struct WidgetUse {
     pub name_span: Span,
 }
 
-impl WidgetUse {
+impl BasicWidgetUse {
     pub fn children_span(&self) -> Span {
         if self.children.is_empty() {
             self.span.point_span_at_end().shifted(-1)
         } else {
-            self.children.first().unwrap().span.to(self.children.last().unwrap().span)
+            self.children.first().unwrap().span().to(self.children.last().unwrap().span())
         }
     }
+
+    fn from_iter<I: Iterator<Item = Ast>>(
+        span: Span,
+        name: String,
+        name_span: Span,
+        mut iter: AstIterator<I>,
+    ) -> AstResult<Self> {
+        let attrs = iter.expect_key_values()?;
+        let children = iter.map(WidgetUse::from_ast).collect::<AstResult<Vec<_>>>()?;
+        Ok(Self { name, attrs, children, span, name_span })
+    }
+}
+
+impl FromAstElementContent for LoopWidgetUse {
+    const ELEMENT_NAME: &'static str = "for";
+
+    fn from_tail<I: Iterator<Item = Ast>>(span: Span, mut iter: AstIterator<I>) -> AstResult<Self> {
+        let (element_name_span, element_name) = iter.expect_symbol()?;
+        let (in_string_span, in_string) = iter.expect_symbol()?;
+        if in_string != "in" {
+            return Err(AstError::FormFormatError(FormFormatError::ExpectedInInForLoop(in_string_span, in_string)));
+        }
+        let (elements_span, elements_expr) = iter.expect_simplexpr()?;
+        let body = iter.expect_any().note("Expected a loop body").and_then(WidgetUse::from_ast)?;
+        iter.expect_done()?;
+        Ok(Self {
+            element_name: VarName(element_name),
+            elements_expr,
+            body: Box::new(body),
+            span,
+            elements_expr_span: elements_span,
+        })
+    }
+}
+
+impl FromAstElementContent for ChildrenWidgetUse {
+    const ELEMENT_NAME: &'static str = "children";
+
+    fn from_tail<I: Iterator<Item = Ast>>(span: Span, mut iter: AstIterator<I>) -> AstResult<Self> {
+        let mut attrs = iter.expect_key_values()?;
+        let nth_expr = attrs.ast_optional("nth")?;
+        iter.expect_done()?;
+        Ok(Self { span, nth_expr })
+    }
 }
 
 impl FromAst for WidgetUse {
     fn from_ast(e: Ast) -> AstResult<Self> {
         let span = e.span();
         if let Ok(value) = e.clone().as_simplexpr() {
-            Ok(label_from_simplexpr(value, span))
+            Ok(WidgetUse::Basic(label_from_simplexpr(value, span)))
         } else {
             let mut iter = e.try_ast_iter()?;
             let (name_span, name) = iter.expect_symbol()?;
-            let attrs = iter.expect_key_values()?;
-            let children = iter.map(WidgetUse::from_ast).collect::<AstResult<Vec<_>>>()?;
-            Ok(Self { name, attrs, children, span, name_span })
+            match name.as_ref() {
+                LoopWidgetUse::ELEMENT_NAME => Ok(WidgetUse::Loop(LoopWidgetUse::from_tail(span, iter)?)),
+                ChildrenWidgetUse::ELEMENT_NAME => Ok(WidgetUse::Children(ChildrenWidgetUse::from_tail(span, iter)?)),
+                _ => Ok(WidgetUse::Basic(BasicWidgetUse::from_iter(span, name, name_span, iter)?)),
+            }
         }
     }
 }
 
-impl Spanned for WidgetUse {
-    fn span(&self) -> Span {
-        self.span
-    }
-}
-
-fn label_from_simplexpr(value: SimplExpr, span: Span) -> WidgetUse {
-    WidgetUse {
+fn label_from_simplexpr(value: SimplExpr, span: Span) -> BasicWidgetUse {
+    BasicWidgetUse {
         name: "label".to_string(),
         name_span: span.point_span(),
         attrs: Attributes::new(
@@ -68,3 +134,15 @@ fn label_from_simplexpr(value: SimplExpr, span: Span) -> WidgetUse {
         span,
     }
 }
+
+macro_rules! impl_spanned {
+    ($($super:ident => $name:ident),*) => {
+        $(impl Spanned for $name { fn span(&self) -> Span { self.span } })*
+        impl Spanned for WidgetUse {
+            fn span(&self) -> Span {
+                match self { $(WidgetUse::$super(widget) => widget.span),* }
+            }
+        }
+    }
+}
+impl_spanned!(Basic => BasicWidgetUse, Loop => LoopWidgetUse, Children => ChildrenWidgetUse);

crates/yuck/src/error.rs

@@ -170,13 +170,17 @@ pub enum FormFormatError {
 
     #[error("Widget definition has more than one child widget")]
     WidgetDefMultipleChildren(Span),
+
+    #[error("Expected 'in' in this position, but got '{}'", .1)]
+    ExpectedInInForLoop(Span, String),
 }
 
 impl Spanned for FormFormatError {
     fn span(&self) -> Span {
         match self {
-            FormFormatError::WidgetDefArglistMissing(span) => *span,
-            FormFormatError::WidgetDefMultipleChildren(span) => *span,
+            FormFormatError::WidgetDefArglistMissing(span)
+            | FormFormatError::WidgetDefMultipleChildren(span)
+            | FormFormatError::ExpectedInInForLoop(span, _) => *span,
         }
     }
 }

crates/yuck/src/format_diagnostic.rs

@@ -298,6 +298,10 @@ impl ToDiagnostic for FormFormatError {
                         To include multiple elements, wrap these elements in a single container widget such as `box`.\n\
                         This is necessary as eww can't know how you want these elements to be layed out otherwise."
             },
+            FormFormatError::ExpectedInInForLoop(span, got) => gen_diagnostic! {
+                msg = self,
+                label = span,
+            },
         }
     }
 }

crates/yuck/src/parser/ast_iterator.rs

@@ -67,6 +67,20 @@ impl<I: Iterator<Item = Ast>> AstIterator<I> {
         self.next().or_missing(self.remaining_span.point_span())
     }
 
+    pub fn expect_simplexpr(&mut self) -> AstResult<(Span, SimplExpr)> {
+        let expr_type = AstType::SimplExpr;
+        match self.expect_any()? {
+            Ast::SimplExpr(span, expr) => Ok((span, expr)),
+            Ast::Symbol(span, var) => Ok((span, SimplExpr::VarRef(span, VarName(var)))),
+            other => {
+                let span = other.span();
+                let actual_type = other.expr_type();
+                self.put_back(other);
+                Err(AstError::WrongExprType(span, expr_type, actual_type))
+            }
+        }
+    }
+
     pub fn expect_done(&mut self) -> AstResult<()> {
         if let Some(next) = self.next() {
             self.put_back(next);

docs/src/configuration.md

@@ -239,7 +239,7 @@ For this, you can make use of one of eww's most powerful features: the `literal`
 (defvar variable_containing_yuck
   "(box (button 'foo') (button 'bar'))")
 
-; then, inside your widget, use:
+; Then, inside your widget, use:
 (literal :content variable_containing_yuck)
 ```
 
@@ -248,6 +248,22 @@ Eww then reads the provided value and renders the resulting widget. Whenever it
 
 Note that this is not all that efficient. Make sure to only use `literal` when necessary!
 
+## Generating a list of widgets from JSON using `for`
+
+If you want to display a list of values, you can use the `for`-Element to fill a container with a list of elements generated from a JSON-array.
+```lisp
+(defvar my-json "[1, 2, 3]")
+
+; Then, inside your widget, you can use
+(box
+  (for entry in my-json
+    (button :onclick "notify-send 'click' 'button ${entry}'"
+      entry)))
+```
+
+This can be useful in many situations, for example when generating a workspace list from a JSON representation of your workspaces.
+In many cases, this can be used instead of `literal`, and should most likely be preferred in those cases.
+
 ## Splitting up your configuration
 
 As time passes, your configuration might grow larger and larger. Luckily, you can easily split up your configuration into multiple files!