7 files changed, 345 insertions, 398 deletions

diff --git a/crates/ra_arena/src/lib.rs b/crates/ra_arena/src/lib.rs
index ea98d5444..441fbb3cb 100644
--- a/crates/ra_arena/src/lib.rs
+++ b/crates/ra_arena/src/lib.rs
@@ -96,6 +96,9 @@ impl<T> Arena<T> {
     pub const fn new() -> Arena<T> {
         Arena { data: Vec::new() }
     }
+    pub fn clear(&mut self) {
+        self.data.clear();
+    }
 
     pub fn len(&self) -> usize {
         self.data.len()
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 6a53be621..bd4ef69a0 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -667,7 +667,7 @@ impl Expectation {
 }
 
 mod diagnostics {
-    use hir_def::{expr::ExprId, src::HasSource, FunctionId, Lookup};
+    use hir_def::{expr::ExprId, FunctionId};
     use hir_expand::diagnostics::DiagnosticSink;
 
     use crate::{db::HirDatabase, diagnostics::NoSuchField};
@@ -686,10 +686,9 @@ mod diagnostics {
         ) {
             match self {
                 InferenceDiagnostic::NoSuchField { expr, field } => {
-                    let source = owner.lookup(db.upcast()).source(db.upcast());
                     let (_, source_map) = db.body_with_source_map(owner.into());
                     let field = source_map.field_syntax(*expr, *field);
-                    sink.push(NoSuchField { file: source.file_id, field: field.value })
+                    sink.push(NoSuchField { file: field.file_id, field: field.value })
                 }
             }
         }
diff --git a/crates/ra_prof/Cargo.toml b/crates/ra_prof/Cargo.toml
index d15b08992..c33b5121a 100644
--- a/crates/ra_prof/Cargo.toml
+++ b/crates/ra_prof/Cargo.toml
@@ -9,6 +9,7 @@ publish = false
 doctest = false
 
 [dependencies]
+ra_arena = { path = "../ra_arena" }
 once_cell = "1.3.1"
 backtrace = { version = "0.3.44", optional = true }
 
diff --git a/crates/ra_prof/src/hprof.rs b/crates/ra_prof/src/hprof.rs
new file mode 100644
index 000000000..2b8a90363
--- /dev/null
+++ b/crates/ra_prof/src/hprof.rs
@@ -0,0 +1,246 @@
+//! Simple hierarchical profiler
+use once_cell::sync::Lazy;
+use std::{
+    cell::RefCell,
+    collections::{BTreeMap, HashSet},
+    io::{stderr, Write},
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        RwLock,
+    },
+    time::{Duration, Instant},
+};
+
+use crate::tree::{Idx, Tree};
+
+/// Filtering syntax
+/// env RA_PROFILE=*             // dump everything
+/// env RA_PROFILE=foo|bar|baz   // enabled only selected entries
+/// env RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms
+pub fn init() {
+    let spec = std::env::var("RA_PROFILE").unwrap_or_default();
+    init_from(&spec);
+}
+
+pub fn init_from(spec: &str) {
+    let filter = if spec.is_empty() { Filter::disabled() } else { Filter::from_spec(spec) };
+    filter.install();
+}
+
+pub type Label = &'static str;
+
+/// This function starts a profiling scope in the current execution stack with a given description.
+/// It returns a Profile structure and measure elapsed time between this method invocation and Profile structure drop.
+/// It supports nested profiling scopes in case when this function invoked multiple times at the execution stack. In this case the profiling information will be nested at the output.
+/// Profiling information is being printed in the stderr.
+///
+/// # Example
+/// ```
+/// use ra_prof::{profile, set_filter, Filter};
+///
+/// let f = Filter::from_spec("profile1|profile2@2");
+/// set_filter(f);
+/// profiling_function1();
+///
+/// fn profiling_function1() {
+///     let _p = profile("profile1");
+///     profiling_function2();
+/// }
+///
+/// fn profiling_function2() {
+///     let _p = profile("profile2");
+/// }
+/// ```
+/// This will print in the stderr the following:
+/// ```text
+///  0ms - profile
+///      0ms - profile2
+/// ```
+pub fn profile(label: Label) -> Profiler {
+    assert!(!label.is_empty());
+    let enabled = PROFILING_ENABLED.load(Ordering::Relaxed)
+        && PROFILE_STACK.with(|stack| stack.borrow_mut().push(label));
+    let label = if enabled { Some(label) } else { None };
+    Profiler { label, detail: None }
+}
+
+pub struct Profiler {
+    label: Option<Label>,
+    detail: Option<String>,
+}
+
+impl Profiler {
+    pub fn detail(mut self, detail: impl FnOnce() -> String) -> Profiler {
+        if self.label.is_some() {
+            self.detail = Some(detail())
+        }
+        self
+    }
+}
+
+impl Drop for Profiler {
+    fn drop(&mut self) {
+        match self {
+            Profiler { label: Some(label), detail } => {
+                PROFILE_STACK.with(|stack| {
+                    stack.borrow_mut().pop(label, detail.take());
+                });
+            }
+            Profiler { label: None, .. } => (),
+        }
+    }
+}
+
+static PROFILING_ENABLED: AtomicBool = AtomicBool::new(false);
+static FILTER: Lazy<RwLock<Filter>> = Lazy::new(Default::default);
+thread_local!(static PROFILE_STACK: RefCell<ProfileStack> = RefCell::new(ProfileStack::new()));
+
+#[derive(Default, Clone, Debug)]
+struct Filter {
+    depth: usize,
+    allowed: HashSet<String>,
+    longer_than: Duration,
+    version: usize,
+}
+
+impl Filter {
+    fn disabled() -> Filter {
+        Filter::default()
+    }
+
+    fn from_spec(mut spec: &str) -> Filter {
+        let longer_than = if let Some(idx) = spec.rfind('>') {
+            let longer_than = spec[idx + 1..].parse().expect("invalid profile longer_than");
+            spec = &spec[..idx];
+            Duration::from_millis(longer_than)
+        } else {
+            Duration::new(0, 0)
+        };
+
+        let depth = if let Some(idx) = spec.rfind('@') {
+            let depth: usize = spec[idx + 1..].parse().expect("invalid profile depth");
+            spec = &spec[..idx];
+            depth
+        } else {
+            999
+        };
+        let allowed =
+            if spec == "*" { HashSet::new() } else { spec.split('|').map(String::from).collect() };
+        Filter { depth, allowed, longer_than, version: 0 }
+    }
+
+    fn install(mut self) {
+        PROFILING_ENABLED.store(self.depth > 0, Ordering::SeqCst);
+        let mut old = FILTER.write().unwrap();
+        self.version = old.version + 1;
+        *old = self;
+    }
+}
+
+struct ProfileStack {
+    starts: Vec<Instant>,
+    filter: Filter,
+    messages: Tree<Message>,
+}
+
+#[derive(Default)]
+struct Message {
+    duration: Duration,
+    label: Label,
+    detail: Option<String>,
+}
+
+impl ProfileStack {
+    fn new() -> ProfileStack {
+        ProfileStack { starts: Vec::new(), messages: Tree::default(), filter: Default::default() }
+    }
+
+    fn push(&mut self, label: Label) -> bool {
+        if self.starts.is_empty() {
+            if let Ok(f) = FILTER.try_read() {
+                if f.version > self.filter.version {
+                    self.filter = f.clone();
+                }
+            };
+        }
+        if self.starts.len() > self.filter.depth {
+            return false;
+        }
+        let allowed = &self.filter.allowed;
+        if self.starts.is_empty() && !allowed.is_empty() && !allowed.contains(label) {
+            return false;
+        }
+
+        self.starts.push(Instant::now());
+        self.messages.start();
+        true
+    }
+
+    pub fn pop(&mut self, label: Label, detail: Option<String>) {
+        let start = self.starts.pop().unwrap();
+        let duration = start.elapsed();
+        let level = self.starts.len();
+        self.messages.finish(Message { duration, label, detail });
+        if level == 0 {
+            let longer_than = self.filter.longer_than;
+            // Convert to millis for comparison to avoid problems with rounding
+            // (otherwise we could print `0ms` despite user's `>0` filter when
+            // `duration` is just a few nanos).
+            if duration.as_millis() > longer_than.as_millis() {
+                let stderr = stderr();
+                if let Some(root) = self.messages.root() {
+                    print(&self.messages, root, 0, longer_than, &mut stderr.lock());
+                }
+            }
+            self.messages.clear();
+            assert!(self.starts.is_empty())
+        }
+    }
+}
+
+fn print(
+    tree: &Tree<Message>,
+    curr: Idx<Message>,
+    level: u32,
+    longer_than: Duration,
+    out: &mut impl Write,
+) {
+    let current_indent = "    ".repeat(level as usize);
+    let detail = tree[curr].detail.as_ref().map(|it| format!(" @ {}", it)).unwrap_or_default();
+    writeln!(
+        out,
+        "{}{:5}ms - {}{}",
+        current_indent,
+        tree[curr].duration.as_millis(),
+        tree[curr].label,
+        detail,
+    )
+    .expect("printing profiling info");
+
+    let mut accounted_for = Duration::default();
+    let mut short_children = BTreeMap::new(); // Use `BTreeMap` to get deterministic output.
+    for child in tree.children(curr) {
+        accounted_for += tree[child].duration;
+
+        if tree[child].duration.as_millis() > longer_than.as_millis() {
+            print(tree, child, level + 1, longer_than, out)
+        } else {
+            let (total_duration, cnt) =
+                short_children.entry(tree[child].label).or_insert((Duration::default(), 0));
+            *total_duration += tree[child].duration;
+            *cnt += 1;
+        }
+    }
+
+    for (child_msg, (duration, count)) in short_children.iter() {
+        let millis = duration.as_millis();
+        writeln!(out, "    {}{:5}ms - {} ({} calls)", current_indent, millis, child_msg, count)
+            .expect("printing profiling info");
+    }
+
+    let unaccounted = tree[curr].duration - accounted_for;
+    if tree.children(curr).next().is_some() && unaccounted > longer_than {
+        writeln!(out, "    {}{:5}ms - ???", current_indent, unaccounted.as_millis())
+            .expect("printing profiling info");
+    }
+}
diff --git a/crates/ra_prof/src/lib.rs b/crates/ra_prof/src/lib.rs
index 2d4f68f5e..89df7f04b 100644
--- a/crates/ra_prof/src/lib.rs
+++ b/crates/ra_prof/src/lib.rs
@@ -1,24 +1,17 @@
-//! FIXME: write short doc here
+//! A collection of tools for profiling rust-analyzer.
 
 mod memory_usage;
 #[cfg(feature = "cpu_profiler")]
 mod google_cpu_profiler;
+mod hprof;
+mod tree;
 
-use std::{
-    cell::RefCell,
-    collections::BTreeMap,
-    collections::HashSet,
-    io::{stderr, Write},
-    sync::{
-        atomic::{AtomicBool, Ordering},
-        RwLock,
-    },
-    time::{Duration, Instant},
-};
-
-use once_cell::sync::Lazy;
+use std::cell::RefCell;
 
-pub use crate::memory_usage::{Bytes, MemoryUsage};
+pub use crate::{
+    hprof::{init, init_from, profile},
+    memory_usage::{Bytes, MemoryUsage},
+};
 
 // We use jemalloc mainly to get heap usage statistics, actual performance
 // difference is not measures.
@@ -26,298 +19,6 @@ pub use crate::memory_usage::{Bytes, MemoryUsage};
 #[global_allocator]
 static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 
-pub fn init() {
-    set_filter(match std::env::var("RA_PROFILE") {
-        Ok(spec) => Filter::from_spec(&spec),
-        Err(_) => Filter::disabled(),
-    });
-}
-
-/// Set profiling filter. It specifies descriptions allowed to profile.
-/// This is helpful when call stack has too many nested profiling scopes.
-/// Additionally filter can specify maximum depth of profiling scopes nesting.
-///
-/// #Example
-/// ```
-/// use ra_prof::{set_filter, Filter};
-/// let f = Filter::from_spec("profile1|profile2@2");
-/// set_filter(f);
-/// ```
-pub fn set_filter(f: Filter) {
-    PROFILING_ENABLED.store(f.depth > 0, Ordering::SeqCst);
-    let set: HashSet<_> = f.allowed.iter().cloned().collect();
-    let mut old = FILTER.write().unwrap();
-    let filter_data = FilterData {
-        depth: f.depth,
-        allowed: set,
-        longer_than: f.longer_than,
-        version: old.version + 1,
-    };
-    *old = filter_data;
-}
-
-pub type Label = &'static str;
-
-/// This function starts a profiling scope in the current execution stack with a given description.
-/// It returns a Profile structure and measure elapsed time between this method invocation and Profile structure drop.
-/// It supports nested profiling scopes in case when this function invoked multiple times at the execution stack. In this case the profiling information will be nested at the output.
-/// Profiling information is being printed in the stderr.
-///
-/// # Example
-/// ```
-/// use ra_prof::{profile, set_filter, Filter};
-///
-/// let f = Filter::from_spec("profile1|profile2@2");
-/// set_filter(f);
-/// profiling_function1();
-///
-/// fn profiling_function1() {
-///     let _p = profile("profile1");
-///     profiling_function2();
-/// }
-///
-/// fn profiling_function2() {
-///     let _p = profile("profile2");
-/// }
-/// ```
-/// This will print in the stderr the following:
-/// ```text
-///  0ms - profile
-///      0ms - profile2
-/// ```
-pub fn profile(label: Label) -> Profiler {
-    assert!(!label.is_empty());
-    if !PROFILING_ENABLED.load(Ordering::Relaxed) {
-        return Profiler { label: None, detail: None };
-    }
-
-    PROFILE_STACK.with(|stack| {
-        let mut stack = stack.borrow_mut();
-        if stack.starts.is_empty() {
-            if let Ok(f) = FILTER.try_read() {
-                if f.version > stack.filter_data.version {
-                    stack.filter_data = f.clone();
-                }
-            };
-        }
-        if stack.starts.len() > stack.filter_data.depth {
-            return Profiler { label: None, detail: None };
-        }
-        let allowed = &stack.filter_data.allowed;
-        if stack.starts.is_empty() && !allowed.is_empty() && !allowed.contains(label) {
-            return Profiler { label: None, detail: None };
-        }
-
-        stack.starts.push(Instant::now());
-        Profiler { label: Some(label), detail: None }
-    })
-}
-
-pub struct Profiler {
-    label: Option<Label>,
-    detail: Option<String>,
-}
-
-impl Profiler {
-    pub fn detail(mut self, detail: impl FnOnce() -> String) -> Profiler {
-        if self.label.is_some() {
-            self.detail = Some(detail())
-        }
-        self
-    }
-}
-
-pub struct Filter {
-    depth: usize,
-    allowed: Vec<String>,
-    longer_than: Duration,
-}
-
-impl Filter {
-    // Filtering syntax
-    // env RA_PROFILE=*             // dump everything
-    // env RA_PROFILE=foo|bar|baz   // enabled only selected entries
-    // env RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms
-    pub fn from_spec(mut spec: &str) -> Filter {
-        let longer_than = if let Some(idx) = spec.rfind('>') {
-            let longer_than = spec[idx + 1..].parse().expect("invalid profile longer_than");
-            spec = &spec[..idx];
-            Duration::from_millis(longer_than)
-        } else {
-            Duration::new(0, 0)
-        };
-
-        let depth = if let Some(idx) = spec.rfind('@') {
-            let depth: usize = spec[idx + 1..].parse().expect("invalid profile depth");
-            spec = &spec[..idx];
-            depth
-        } else {
-            999
-        };
-        let allowed =
-            if spec == "*" { Vec::new() } else { spec.split('|').map(String::from).collect() };
-        Filter::new(depth, allowed, longer_than)
-    }
-
-    pub fn disabled() -> Filter {
-        Filter::new(0, Vec::new(), Duration::new(0, 0))
-    }
-
-    pub fn new(depth: usize, allowed: Vec<String>, longer_than: Duration) -> Filter {
-        Filter { depth, allowed, longer_than }
-    }
-}
-
-struct ProfileStack {
-    starts: Vec<Instant>,
-    messages: Vec<Message>,
-    filter_data: FilterData,
-}
-
-struct Message {
-    level: usize,
-    duration: Duration,
-    label: Label,
-    detail: Option<String>,
-}
-
-impl ProfileStack {
-    fn new() -> ProfileStack {
-        ProfileStack { starts: Vec::new(), messages: Vec::new(), filter_data: Default::default() }
-    }
-}
-
-#[derive(Default, Clone)]
-struct FilterData {
-    depth: usize,
-    version: usize,
-    allowed: HashSet<String>,
-    longer_than: Duration,
-}
-
-static PROFILING_ENABLED: AtomicBool = AtomicBool::new(false);
-
-static FILTER: Lazy<RwLock<FilterData>> = Lazy::new(Default::default);
-
-thread_local!(static PROFILE_STACK: RefCell<ProfileStack> = RefCell::new(ProfileStack::new()));
-
-impl Drop for Profiler {
-    fn drop(&mut self) {
-        match self {
-            Profiler { label: Some(label), detail } => {
-                PROFILE_STACK.with(|stack| {
-                    let mut stack = stack.borrow_mut();
-                    let start = stack.starts.pop().unwrap();
-                    let duration = start.elapsed();
-                    let level = stack.starts.len();
-                    stack.messages.push(Message { level, duration, label, detail: detail.take() });
-                    if level == 0 {
-                        let stdout = stderr();
-                        let longer_than = stack.filter_data.longer_than;
-                        // Convert to millis for comparison to avoid problems with rounding
-                        // (otherwise we could print `0ms` despite user's `>0` filter when
-                        // `duration` is just a few nanos).
-                        if duration.as_millis() > longer_than.as_millis() {
-                            print(&stack.messages, longer_than, &mut stdout.lock());
-                        }
-                        stack.messages.clear();
-                    }
-                });
-            }
-            Profiler { label: None, .. } => (),
-        }
-    }
-}
-
-fn print(msgs: &[Message], longer_than: Duration, out: &mut impl Write) {
-    if msgs.is_empty() {
-        return;
-    }
-    let children_map = idx_to_children(msgs);
-    let root_idx = msgs.len() - 1;
-    print_for_idx(root_idx, &children_map, msgs, longer_than, out);
-}
-
-fn print_for_idx(
-    current_idx: usize,
-    children_map: &[Vec<usize>],
-    msgs: &[Message],
-    longer_than: Duration,
-    out: &mut impl Write,
-) {
-    let current = &msgs[current_idx];
-    let current_indent = "    ".repeat(current.level);
-    let detail = current.detail.as_ref().map(|it| format!(" @ {}", it)).unwrap_or_default();
-    writeln!(
-        out,
-        "{}{:5}ms - {}{}",
-        current_indent,
-        current.duration.as_millis(),
-        current.label,
-        detail,
-    )
-    .expect("printing profiling info");
-
-    let longer_than_millis = longer_than.as_millis();
-    let children_indices = &children_map[current_idx];
-    let mut accounted_for = Duration::default();
-    let mut short_children = BTreeMap::new(); // Use `BTreeMap` to get deterministic output.
-
-    for child_idx in children_indices.iter() {
-        let child = &msgs[*child_idx];
-        if child.duration.as_millis() > longer_than_millis {
-            print_for_idx(*child_idx, children_map, msgs, longer_than, out);
-        } else {
-            let pair = short_children.entry(child.label).or_insert((Duration::default(), 0));
-            pair.0 += child.duration;
-            pair.1 += 1;
-        }
-        accounted_for += child.duration;
-    }
-
-    for (child_msg, (duration, count)) in short_children.iter() {
-        let millis = duration.as_millis();
-        writeln!(out, "    {}{:5}ms - {} ({} calls)", current_indent, millis, child_msg, count)
-            .expect("printing profiling info");
-    }
-
-    let unaccounted_millis = (current.duration - accounted_for).as_millis();
-    if !children_indices.is_empty()
-        && unaccounted_millis > 0
-        && unaccounted_millis > longer_than_millis
-    {
-        writeln!(out, "    {}{:5}ms - ???", current_indent, unaccounted_millis)
-            .expect("printing profiling info");
-    }
-}
-
-/// Returns a mapping from an index in the `msgs` to the vector with the indices of its children.
-///
-/// This assumes that the entries in `msgs` are in the order of when the calls to `profile` finish.
-/// In other words, a postorder of the call graph. In particular, the root is the last element of
-/// `msgs`.
-fn idx_to_children(msgs: &[Message]) -> Vec<Vec<usize>> {
-    // Initialize with the index of the root; `msgs` and `ancestors` should be never empty.
-    assert!(!msgs.is_empty());
-    let mut ancestors = vec![msgs.len() - 1];
-    let mut result: Vec<Vec<usize>> = vec![vec![]; msgs.len()];
-    for (idx, msg) in msgs[..msgs.len() - 1].iter().enumerate().rev() {
-        // We need to find the parent of the current message, i.e., the last ancestor that has a
-        // level lower than the current message.
-        while msgs[*ancestors.last().unwrap()].level >= msg.level {
-            ancestors.pop();
-        }
-        result[*ancestors.last().unwrap()].push(idx);
-        ancestors.push(idx);
-    }
-    // Note that above we visited all children from the last to the first one. Let's reverse vectors
-    // to get the more natural order where the first element is the first child.
-    for vec in result.iter_mut() {
-        vec.reverse();
-    }
-    result
-}
-
 /// Prints backtrace to stderr, useful for debugging.
 #[cfg(feature = "backtrace")]
 pub fn print_backtrace() {
@@ -403,86 +104,3 @@ impl Drop for CpuProfiler {
 pub fn memory_usage() -> MemoryUsage {
     MemoryUsage::current()
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_basic_profile() {
-        let s = vec!["profile1".to_string(), "profile2".to_string()];
-        let f = Filter::new(2, s, Duration::new(0, 0));
-        set_filter(f);
-        profiling_function1();
-    }
-
-    fn profiling_function1() {
-        let _p = profile("profile1");
-        profiling_function2();
-    }
-
-    fn profiling_function2() {
-        let _p = profile("profile2");
-    }
-
-    #[test]
-    fn test_longer_than() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 1, duration: Duration::from_nanos(3), label: "bar", detail: None },
-            Message { level: 1, duration: Duration::from_nanos(2), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(1), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        // The calls to `bar` are so short that they'll be rounded to 0ms and should get collapsed
-        // when printing.
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap(),
-            "    1ms - foo\n        0ms - bar (2 calls)\n"
-        );
-    }
-
-    #[test]
-    fn test_unaccounted_for_topmost() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 1, duration: Duration::from_millis(2), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(5), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap().lines().collect::<Vec<_>>(),
-            vec![
-                "    5ms - foo",
-                "        2ms - bar",
-                "        3ms - ???",
-                // Dummy comment to improve formatting
-            ]
-        );
-    }
-
-    #[test]
-    fn test_unaccounted_for_multiple_levels() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 2, duration: Duration::from_millis(3), label: "baz", detail: None },
-            Message { level: 1, duration: Duration::from_millis(5), label: "bar", detail: None },
-            Message { level: 2, duration: Duration::from_millis(2), label: "baz", detail: None },
-            Message { level: 1, duration: Duration::from_millis(4), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(9), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap().lines().collect::<Vec<_>>(),
-            vec![
-                "    9ms - foo",
-                "        5ms - bar",
-                "            3ms - baz",
-                "            2ms - ???",
-                "        4ms - bar",
-                "            2ms - baz",
-                "            2ms - ???",
-            ]
-        );
-    }
-}
diff --git a/crates/ra_prof/src/tree.rs b/crates/ra_prof/src/tree.rs
new file mode 100644
index 000000000..9ea5b5db8
--- /dev/null
+++ b/crates/ra_prof/src/tree.rs
@@ -0,0 +1,84 @@
+//! A simple tree implementation which tries to not allocate all over the place.
+use std::ops;
+
+use ra_arena::Arena;
+
+#[derive(Default)]
+pub struct Tree<T> {
+    nodes: Arena<Node<T>>,
+    current_path: Vec<(Idx<T>, Option<Idx<T>>)>,
+}
+
+pub type Idx<T> = ra_arena::Idx<Node<T>>;
+
+impl<T> Tree<T> {
+    pub fn start(&mut self)
+    where
+        T: Default,
+    {
+        let me = self.nodes.alloc(Node::new(T::default()));
+        if let Some((parent, last_child)) = self.current_path.last_mut() {
+            let slot = match *last_child {
+                Some(last_child) => &mut self.nodes[last_child].next_sibling,
+                None => &mut self.nodes[*parent].first_child,
+            };
+            let prev = slot.replace(me);
+            assert!(prev.is_none());
+            *last_child = Some(me);
+        }
+
+        self.current_path.push((me, None));
+    }
+
+    pub fn finish(&mut self, data: T) {
+        let (me, _last_child) = self.current_path.pop().unwrap();
+        self.nodes[me].data = data;
+    }
+
+    pub fn root(&self) -> Option<Idx<T>> {
+        self.nodes.iter().next().map(|(idx, _)| idx)
+    }
+
+    pub fn children(&self, idx: Idx<T>) -> impl Iterator<Item = Idx<T>> + '_ {
+        NodeIter { nodes: &self.nodes, next: self.nodes[idx].first_child }
+    }
+    pub fn clear(&mut self) {
+        self.nodes.clear();
+        self.current_path.clear();
+    }
+}
+
+impl<T> ops::Index<Idx<T>> for Tree<T> {
+    type Output = T;
+    fn index(&self, index: Idx<T>) -> &T {
+        &self.nodes[index].data
+    }
+}
+
+pub struct Node<T> {
+    data: T,
+    first_child: Option<Idx<T>>,
+    next_sibling: Option<Idx<T>>,
+}
+
+impl<T> Node<T> {
+    fn new(data: T) -> Node<T> {
+        Node { data, first_child: None, next_sibling: None }
+    }
+}
+
+struct NodeIter<'a, T> {
+    nodes: &'a Arena<Node<T>>,
+    next: Option<Idx<T>>,
+}
+
+impl<'a, T> Iterator for NodeIter<'a, T> {
+    type Item = Idx<T>;
+
+    fn next(&mut self) -> Option<Idx<T>> {
+        self.next.map(|next| {
+            self.next = self.nodes[next].next_sibling;
+            next
+        })
+    }
+}
diff --git a/crates/rust-analyzer/tests/heavy_tests/support.rs b/crates/rust-analyzer/tests/heavy_tests/support.rs
index 7eebedff7..e4fe3411a 100644
--- a/crates/rust-analyzer/tests/heavy_tests/support.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/support.rs
@@ -62,11 +62,7 @@ impl<'a> Project<'a> {
         static INIT: Once = Once::new();
         INIT.call_once(|| {
             env_logger::builder().is_test(true).try_init().unwrap();
-            ra_prof::set_filter(if crate::PROFILE.is_empty() {
-                ra_prof::Filter::disabled()
-            } else {
-                ra_prof::Filter::from_spec(&crate::PROFILE)
-            });
+            ra_prof::init_from(crate::PROFILE);
         });
 
         let mut paths = vec![];