3 files changed, 94 insertions, 20 deletions

diff --git a/src/ide/analyze.rs b/src/ide/analyze.rs
new file mode 100644
index 00000000..d8925cfc
--- /dev/null
+++ b/src/ide/analyze.rs
@@ -0,0 +1,38 @@
+use comemo::Track;
+
+use crate::model::{eval, Route, Tracer, Value};
+use crate::syntax::{ast, LinkedNode, SyntaxKind};
+use crate::World;
+
+/// Try to determine a set of possible values for an expression.
+pub fn analyze(world: &(dyn World + 'static), node: &LinkedNode) -> Vec<Value> {
+    match node.cast::<ast::Expr>() {
+        Some(ast::Expr::Ident(_) | ast::Expr::MathIdent(_)) => {
+            if let Some(parent) = node.parent() {
+                if parent.kind() == SyntaxKind::FieldAccess && node.index() > 0 {
+                    return analyze(world, parent);
+                }
+            }
+
+            let span = node.span();
+            let source = world.source(span.source());
+            let route = Route::default();
+            let mut tracer = Tracer::new(Some(span));
+            eval(world.track(), route.track(), tracer.track_mut(), source).ok();
+            return tracer.finish();
+        }
+
+        Some(ast::Expr::FieldAccess(access)) => {
+            if let Some(child) = node.children().next() {
+                return analyze(world, &child)
+                    .into_iter()
+                    .filter_map(|target| target.field(&access.field()).ok())
+                    .collect();
+            }
+        }
+
+        _ => {}
+    }
+
+    vec![]
+}
diff --git a/src/ide/mod.rs b/src/ide/mod.rs
index f52fa076..ac69b38a 100644
--- a/src/ide/mod.rs
+++ b/src/ide/mod.rs
@@ -1,9 +1,11 @@
 //! Capabilities for IDE support.
 
+mod analyze;
 mod complete;
 mod highlight;
 mod tooltip;
 
+pub use analyze::*;
 pub use complete::*;
 pub use highlight::*;
 pub use tooltip::*;
diff --git a/src/ide/tooltip.rs b/src/ide/tooltip.rs
index 076e2b45..202efd8e 100644
--- a/src/ide/tooltip.rs
+++ b/src/ide/tooltip.rs
@@ -1,40 +1,71 @@
 use if_chain::if_chain;
+use unicode_segmentation::UnicodeSegmentation;
 
-use super::{plain_docs_sentence, summarize_font_family};
-use crate::model::{CastInfo, Value};
+use super::{analyze, plain_docs_sentence, summarize_font_family};
+use crate::model::{CastInfo, Tracer, Value};
 use crate::syntax::ast;
 use crate::syntax::{LinkedNode, Source, SyntaxKind};
 use crate::World;
 
 /// Describe the item under the cursor.
-pub fn tooltip(world: &dyn World, source: &Source, cursor: usize) -> Option<String> {
+pub fn tooltip(
+    world: &(dyn World + 'static),
+    source: &Source,
+    cursor: usize,
+) -> Option<String> {
     let leaf = LinkedNode::new(source.root()).leaf_at(cursor)?;
 
-    function_tooltip(world, &leaf)
-        .or_else(|| named_param_tooltip(world, &leaf))
+    named_param_tooltip(world, &leaf)
         .or_else(|| font_family_tooltip(world, &leaf))
+        .or_else(|| expr_tooltip(world, &leaf))
 }
 
-/// Tooltip for a function or set rule name.
-fn function_tooltip(world: &dyn World, leaf: &LinkedNode) -> Option<String> {
-    if_chain! {
-        if let Some(ident) = leaf.cast::<ast::Ident>();
-        if matches!(
-            leaf.parent_kind(),
-            Some(SyntaxKind::FuncCall | SyntaxKind::SetRule),
-        );
-        if let Some(Value::Func(func)) = world.library().global.scope().get(&ident);
-        if let Some(info) = func.info();
-        then {
-            return Some(plain_docs_sentence(info.docs));
+/// Tooltip for a hovered expression.
+fn expr_tooltip(world: &(dyn World + 'static), leaf: &LinkedNode) -> Option<String> {
+    if !leaf.is::<ast::Expr>() {
+        return None;
+    }
+
+    let values = analyze(world, leaf);
+    if let [value] = values.as_slice() {
+        if let Some(docs) = value.docs() {
+            return Some(plain_docs_sentence(docs));
         }
     }
 
-    None
+    let mut tooltip = String::new();
+    let mut iter = values.into_iter().enumerate();
+    for (i, value) in (&mut iter).take(Tracer::MAX - 1) {
+        if i > 0 && !tooltip.is_empty() {
+            tooltip.push_str(", ");
+        }
+        let repr = value.repr();
+        let repr = repr.as_str();
+        let len = repr.len();
+        if len <= 40 {
+            tooltip.push_str(repr);
+        } else {
+            let mut graphemes = repr.graphemes(true);
+            let r = graphemes.next_back().map_or(0, str::len);
+            let l = graphemes.take(40).map(str::len).sum();
+            tooltip.push_str(&repr[..l]);
+            tooltip.push_str("...");
+            tooltip.push_str(&repr[len - r..]);
+        }
+    }
+
+    if iter.next().is_some() {
+        tooltip.push_str(", ...");
+    }
+
+    (!tooltip.is_empty()).then(|| tooltip)
 }
 
 /// Tooltips for components of a named parameter.
-fn named_param_tooltip(world: &dyn World, leaf: &LinkedNode) -> Option<String> {
+fn named_param_tooltip(
+    world: &(dyn World + 'static),
+    leaf: &LinkedNode,
+) -> Option<String> {
     let (info, named) = if_chain! {
         // Ensure that we are in a named pair in the arguments to a function
         // call or set rule.
@@ -92,7 +123,10 @@ fn find_string_doc(info: &CastInfo, string: &str) -> Option<&'static str> {
 }
 
 /// Tooltip for font family.
-fn font_family_tooltip(world: &dyn World, leaf: &LinkedNode) -> Option<String> {
+fn font_family_tooltip(
+    world: &(dyn World + 'static),
+    leaf: &LinkedNode,
+) -> Option<String> {
     if_chain! {
         // Ensure that we are on top of a string.
         if let Some(string) = leaf.cast::<ast::Str>();