Tracing-based expression tooltips

10 files changed, 199 insertions, 47 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>();
diff --git a/src/lib.rs b/src/lib.rs
index e6410d84..4d4cbb8b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -51,6 +51,7 @@ pub mod syntax;
 use std::path::Path;
 
 use comemo::{Prehashed, Track};
+use model::Tracer;
 
 use crate::diag::{FileResult, SourceResult};
 use crate::doc::Document;
@@ -63,7 +64,8 @@ use crate::util::Buffer;
 pub fn compile(world: &(dyn World + 'static), source: &Source) -> SourceResult<Document> {
     // Evaluate the source file into a module.
     let route = Route::default();
-    let module = model::eval(world.track(), route.track(), source)?;
+    let mut tracer = Tracer::default();
+    let module = model::eval(world.track(), route.track(), tracer.track_mut(), source)?;
 
     // Typeset the module's contents.
     model::typeset(world.track(), &module.content())
diff --git a/src/model/array.rs b/src/model/array.rs
index 0071d4f4..be35c651 100644
--- a/src/model/array.rs
+++ b/src/model/array.rs
@@ -136,7 +136,7 @@ impl Array {
     }
 
     /// Return the first matching element.
-    pub fn find(&self, vm: &Vm, func: Func) -> SourceResult<Option<Value>> {
+    pub fn find(&self, vm: &mut Vm, func: Func) -> SourceResult<Option<Value>> {
         if func.argc().map_or(false, |count| count != 1) {
             bail!(func.span(), "function must have exactly one parameter");
         }
@@ -151,7 +151,7 @@ impl Array {
     }
 
     /// Return the index of the first matching element.
-    pub fn position(&self, vm: &Vm, func: Func) -> SourceResult<Option<i64>> {
+    pub fn position(&self, vm: &mut Vm, func: Func) -> SourceResult<Option<i64>> {
         if func.argc().map_or(false, |count| count != 1) {
             bail!(func.span(), "function must have exactly one parameter");
         }
@@ -167,7 +167,7 @@ impl Array {
 
     /// Return a new array with only those elements for which the function
     /// returns true.
-    pub fn filter(&self, vm: &Vm, func: Func) -> SourceResult<Self> {
+    pub fn filter(&self, vm: &mut Vm, func: Func) -> SourceResult<Self> {
         if func.argc().map_or(false, |count| count != 1) {
             bail!(func.span(), "function must have exactly one parameter");
         }
@@ -182,7 +182,7 @@ impl Array {
     }
 
     /// Transform each item in the array with a function.
-    pub fn map(&self, vm: &Vm, func: Func) -> SourceResult<Self> {
+    pub fn map(&self, vm: &mut Vm, func: Func) -> SourceResult<Self> {
         if func.argc().map_or(false, |count| !(1..=2).contains(&count)) {
             bail!(func.span(), "function must have one or two parameters");
         }
@@ -201,7 +201,7 @@ impl Array {
     }
 
     /// Fold all of the array's elements into one with a function.
-    pub fn fold(&self, vm: &Vm, init: Value, func: Func) -> SourceResult<Value> {
+    pub fn fold(&self, vm: &mut Vm, init: Value, func: Func) -> SourceResult<Value> {
         if func.argc().map_or(false, |count| count != 2) {
             bail!(func.span(), "function must have exactly two parameters");
         }
@@ -214,7 +214,7 @@ impl Array {
     }
 
     /// Whether any element matches.
-    pub fn any(&self, vm: &Vm, func: Func) -> SourceResult<bool> {
+    pub fn any(&self, vm: &mut Vm, func: Func) -> SourceResult<bool> {
         if func.argc().map_or(false, |count| count != 1) {
             bail!(func.span(), "function must have exactly one parameter");
         }
@@ -229,7 +229,7 @@ impl Array {
     }
 
     /// Whether all elements match.
-    pub fn all(&self, vm: &Vm, func: Func) -> SourceResult<bool> {
+    pub fn all(&self, vm: &mut Vm, func: Func) -> SourceResult<bool> {
         if func.argc().map_or(false, |count| count != 1) {
             bail!(func.span(), "function must have exactly one parameter");
         }
diff --git a/src/model/dict.rs b/src/model/dict.rs
index e94db923..76d194a8 100644
--- a/src/model/dict.rs
+++ b/src/model/dict.rs
@@ -105,7 +105,7 @@ impl Dict {
     }
 
     /// Transform each pair in the dictionary with a function.
-    pub fn map(&self, vm: &Vm, func: Func) -> SourceResult<Array> {
+    pub fn map(&self, vm: &mut Vm, func: Func) -> SourceResult<Array> {
         if func.argc().map_or(false, |count| count != 2) {
             bail!(func.span(), "function must have exactly two parameters");
         }
diff --git a/src/model/eval.rs b/src/model/eval.rs
index 6a1884eb..50d0ffc3 100644
--- a/src/model/eval.rs
+++ b/src/model/eval.rs
@@ -4,7 +4,7 @@ use std::collections::BTreeMap;
 use std::mem;
 use std::path::{Path, PathBuf};
 
-use comemo::{Track, Tracked};
+use comemo::{Track, Tracked, TrackedMut};
 use unicode_segmentation::UnicodeSegmentation;
 
 use super::{
@@ -17,7 +17,7 @@ use crate::diag::{
 use crate::geom::{Abs, Angle, Em, Fr, Ratio};
 use crate::syntax::ast::AstNode;
 use crate::syntax::{ast, Source, SourceId, Span, Spanned, SyntaxKind, SyntaxNode};
-use crate::util::{EcoString, PathExt};
+use crate::util::PathExt;
 use crate::World;
 
 const MAX_ITERATIONS: usize = 10_000;
@@ -28,6 +28,7 @@ const MAX_CALL_DEPTH: usize = 256;
 pub fn eval(
     world: Tracked<dyn World>,
     route: Tracked<Route>,
+    tracer: TrackedMut<Tracer>,
     source: &Source,
 ) -> SourceResult<Module> {
     // Prevent cyclic evaluation.
@@ -44,7 +45,7 @@ pub fn eval(
     // Evaluate the module.
     let route = unsafe { Route::insert(route, id) };
     let scopes = Scopes::new(Some(library));
-    let mut vm = Vm::new(world, route.track(), id, scopes, 0);
+    let mut vm = Vm::new(world, route.track(), tracer, id, scopes, 0);
     let result = source.ast()?.eval(&mut vm);
 
     // Handle control flow.
@@ -68,6 +69,8 @@ pub struct Vm<'a> {
     pub(super) items: LangItems,
     /// The route of source ids the VM took to reach its current location.
     pub(super) route: Tracked<'a, Route>,
+    /// The tracer for inspection of the values an expression produces.
+    pub(super) tracer: TrackedMut<'a, Tracer>,
     /// The current location.
     pub(super) location: SourceId,
     /// A control flow event that is currently happening.
@@ -76,6 +79,8 @@ pub struct Vm<'a> {
     pub(super) scopes: Scopes<'a>,
     /// The current call depth.
     pub(super) depth: usize,
+    /// A span that is currently traced.
+    pub(super) traced: Option<Span>,
 }
 
 impl<'a> Vm<'a> {
@@ -83,18 +88,22 @@ impl<'a> Vm<'a> {
     pub(super) fn new(
         world: Tracked<'a, dyn World>,
         route: Tracked<'a, Route>,
+        tracer: TrackedMut<'a, Tracer>,
         location: SourceId,
         scopes: Scopes<'a>,
         depth: usize,
     ) -> Self {
+        let traced = tracer.span(location);
         Self {
             world,
             items: world.library().items.clone(),
             route,
+            tracer,
             location,
             flow: None,
             scopes,
             depth,
+            traced,
         }
     }
 
@@ -103,6 +112,15 @@ impl<'a> Vm<'a> {
         self.world
     }
 
+    /// Define a variable in the current scope.
+    pub fn define(&mut self, var: ast::Ident, value: impl Into<Value>) {
+        let value = value.into();
+        if self.traced == Some(var.span()) {
+            self.tracer.trace(value.clone());
+        }
+        self.scopes.top.define(var.take(), value);
+    }
+
     /// Resolve a user-entered path to be relative to the compilation
     /// environment's root.
     pub fn locate(&self, path: &str) -> StrResult<PathBuf> {
@@ -182,6 +200,47 @@ impl Route {
     }
 }
 
+/// Traces which values existed for the expression with the given span.
+#[derive(Default, Clone)]
+pub struct Tracer {
+    span: Option<Span>,
+    values: Vec<Value>,
+}
+
+impl Tracer {
+    /// The maximum number of traced items.
+    pub const MAX: usize = 10;
+
+    /// Create a new tracer, possibly with a span under inspection.
+    pub fn new(span: Option<Span>) -> Self {
+        Self { span, values: vec![] }
+    }
+
+    /// Get the traced values.
+    pub fn finish(self) -> Vec<Value> {
+        self.values
+    }
+}
+
+#[comemo::track]
+impl Tracer {
+    /// The traced span if it is part of the given source file.
+    fn span(&self, id: SourceId) -> Option<Span> {
+        if self.span.map(Span::source) == Some(id) {
+            self.span
+        } else {
+            None
+        }
+    }
+
+    /// Trace a value for the span.
+    fn trace(&mut self, v: Value) {
+        if self.values.len() < Self::MAX {
+            self.values.push(v);
+        }
+    }
+}
+
 /// Evaluate an expression.
 pub(super) trait Eval {
     /// The output of evaluating the expression.
@@ -259,12 +318,11 @@ impl Eval for ast::Expr {
             error!(span, "{} is only allowed directly in code and content blocks", name)
         };
 
-        match self {
+        let v = match self {
             Self::Text(v) => v.eval(vm).map(Value::Content),
             Self::Space(v) => v.eval(vm).map(Value::Content),
             Self::Linebreak(v) => v.eval(vm).map(Value::Content),
             Self::Parbreak(v) => v.eval(vm).map(Value::Content),
-            Self::Symbol(v) => v.eval(vm).map(Value::Content),
             Self::Escape(v) => v.eval(vm),
             Self::Shorthand(v) => v.eval(vm),
             Self::SmartQuote(v) => v.eval(vm).map(Value::Content),
@@ -319,6 +377,8 @@ impl Eval for ast::Expr {
         }?
         .spanned(span);
 
+        if vm.traced == Some(span) {
+            vm.tracer.trace(v.clone());
         }
 
         Ok(v)
@@ -1049,7 +1109,7 @@ impl Eval for ast::LetBinding {
             Some(expr) => expr.eval(vm)?,
             None => Value::None,
         };
-        vm.scopes.top.define(self.binding().take(), value);
+        vm.define(self.binding(), value);
         Ok(Value::None)
     }
 }
@@ -1183,7 +1243,7 @@ impl Eval for ast::ForLoop {
 
                 #[allow(unused_parens)]
                 for ($($value),*) in $iter {
-                    $(vm.scopes.top.define($binding.clone(), $value);)*
+                    $(vm.define($binding.clone(), $value);)*
 
                     let body = self.body();
                     let value = body.eval(vm)?;
@@ -1206,8 +1266,8 @@ impl Eval for ast::ForLoop {
 
         let iter = self.iter().eval(vm)?;
         let pattern = self.pattern();
-        let key = pattern.key().map(ast::Ident::take);
-        let value = pattern.value().take();
+        let key = pattern.key();
+        let value = pattern.value();
 
         match (key, value, iter) {
             (None, v, Value::Str(string)) => {
@@ -1271,7 +1331,7 @@ impl Eval for ast::ModuleImport {
                 let mut errors = vec![];
                 for ident in idents {
                     if let Some(value) = module.scope().get(&ident) {
-                        vm.scopes.top.define(ident.take(), value.clone());
+                        vm.define(ident, value.clone());
                     } else {
                         errors.push(error!(ident.span(), "unresolved import"));
                     }
diff --git a/src/model/func.rs b/src/model/func.rs
index 00e59bbd..8cf3ea99 100644
--- a/src/model/func.rs
+++ b/src/model/func.rs
@@ -2,11 +2,11 @@ use std::fmt::{self, Debug, Formatter};
 use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
-use comemo::{Track, Tracked};
+use comemo::{Track, Tracked, TrackedMut};
 
 use super::{
     Args, CastInfo, Dict, Eval, Flow, Node, NodeId, Route, Scope, Scopes, Selector,
-    StyleMap, Value, Vm,
+    StyleMap, Tracer, Value, Vm,
 };
 use crate::diag::{bail, SourceResult, StrResult};
 use crate::syntax::ast::{self, AstNode, Expr};
@@ -110,7 +110,7 @@ impl Func {
     }
 
     /// Call the function with the given arguments.
-    pub fn call(&self, vm: &Vm, mut args: Args) -> SourceResult<Value> {
+    pub fn call(&self, vm: &mut Vm, mut args: Args) -> SourceResult<Value> {
         let value = match self.0.as_ref() {
             Repr::Native(native) => (native.func)(vm, &mut args)?,
             Repr::Closure(closure) => closure.call(vm, self, &mut args)?,
@@ -132,8 +132,9 @@ impl Func {
         let route = Route::default();
         let id = SourceId::detached();
         let scopes = Scopes::new(None);
-        let vm = Vm::new(world, route.track(), id, scopes, 0);
-        self.call(&vm, args)
+        let mut tracer = Tracer::default();
+        let mut vm = Vm::new(world, route.track(), tracer.track_mut(), id, scopes, 0);
+        self.call(&mut vm, args)
     }
 
     /// Apply the given arguments to the function.
@@ -292,7 +293,7 @@ pub(super) struct Closure {
 
 impl Closure {
     /// Call the function in the context with the arguments.
-    fn call(&self, vm: &Vm, this: &Func, args: &mut Args) -> SourceResult<Value> {
+    fn call(&self, vm: &mut Vm, this: &Func, args: &mut Args) -> SourceResult<Value> {
         // Don't leak the scopes from the call site. Instead, we use the scope
         // of captured variables we collected earlier.
         let mut scopes = Scopes::new(None);
@@ -327,7 +328,14 @@ impl Closure {
         let route = if detached { fresh.track() } else { vm.route };
 
         // Evaluate the body.
-        let mut sub = Vm::new(vm.world, route, self.location, scopes, vm.depth + 1);
+        let mut sub = Vm::new(
+            vm.world,
+            route,
+            TrackedMut::reborrow_mut(&mut vm.tracer),
+            self.location,
+            scopes,
+            vm.depth + 1,
+        );
         let result = self.body.eval(&mut sub);
 
         // Handle control flow.
diff --git a/src/model/methods.rs b/src/model/methods.rs
index f80839f8..173b95fe 100644
--- a/src/model/methods.rs
+++ b/src/model/methods.rs
@@ -7,7 +7,7 @@ use crate::util::EcoString;
 
 /// Call a method on a value.
 pub fn call(
-    vm: &Vm,
+    vm: &mut Vm,
     value: Value,
     method: &str,
     mut args: Args,
diff --git a/src/model/value.rs b/src/model/value.rs
index 15656c42..ba3a550f 100644
--- a/src/model/value.rs
+++ b/src/model/value.rs
@@ -155,6 +155,14 @@ impl Value {
             _ => self.display(),
         }
     }
+
+    /// Try to extract documentation for the value.
+    pub fn docs(&self) -> Option<&'static str> {
+        match self {
+            Self::Func(func) => func.info().map(|info| info.docs),
+            _ => None,
+        }
+    }
 }
 
 impl Default for Value {