16 files changed, 362 insertions, 90 deletions

diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index cc72964ff..1b3525011 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -1189,7 +1189,7 @@ impl Type {
             None => return false,
         };
 
-        let canonical_ty = Canonical { value: self.ty.value.clone(), num_vars: 0 };
+        let canonical_ty = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
         method_resolution::implements_trait(
             &canonical_ty,
             db,
@@ -1213,7 +1213,7 @@ impl Type {
                 self.ty.environment.clone(),
                 hir_ty::Obligation::Trait(trait_ref),
             ),
-            num_vars: 0,
+            kinds: Arc::new([]),
         };
 
         db.trait_solve(self.krate, goal).is_some()
@@ -1288,7 +1288,7 @@ impl Type {
     pub fn autoderef<'a>(&'a self, db: &'a dyn HirDatabase) -> impl Iterator<Item = Type> + 'a {
         // There should be no inference vars in types passed here
         // FIXME check that?
-        let canonical = Canonical { value: self.ty.value.clone(), num_vars: 0 };
+        let canonical = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
         let environment = self.ty.environment.clone();
         let ty = InEnvironment { value: canonical, environment };
         autoderef(db, Some(self.krate), ty)
@@ -1329,7 +1329,7 @@ impl Type {
         // There should be no inference vars in types passed here
         // FIXME check that?
         // FIXME replace Unknown by bound vars here
-        let canonical = Canonical { value: self.ty.value.clone(), num_vars: 0 };
+        let canonical = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
 
         let env = self.ty.environment.clone();
         let krate = krate.id;
@@ -1360,7 +1360,7 @@ impl Type {
         // There should be no inference vars in types passed here
         // FIXME check that?
         // FIXME replace Unknown by bound vars here
-        let canonical = Canonical { value: self.ty.value.clone(), num_vars: 0 };
+        let canonical = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
 
         let env = self.ty.environment.clone();
         let krate = krate.id;
diff --git a/crates/ra_hir_ty/src/autoderef.rs b/crates/ra_hir_ty/src/autoderef.rs
index 1b0f84c5c..c727012c6 100644
--- a/crates/ra_hir_ty/src/autoderef.rs
+++ b/crates/ra_hir_ty/src/autoderef.rs
@@ -37,7 +37,7 @@ pub(crate) fn deref(
     ty: InEnvironment<&Canonical<Ty>>,
 ) -> Option<Canonical<Ty>> {
     if let Some(derefed) = ty.value.value.builtin_deref() {
-        Some(Canonical { value: derefed, num_vars: ty.value.num_vars })
+        Some(Canonical { value: derefed, kinds: ty.value.kinds.clone() })
     } else {
         deref_by_trait(db, krate, ty)
     }
@@ -68,8 +68,8 @@ fn deref_by_trait(
 
     // Check that the type implements Deref at all
     let trait_ref = TraitRef { trait_: deref_trait, substs: parameters.clone() };
-    let implements_goal = super::Canonical {
-        num_vars: ty.value.num_vars,
+    let implements_goal = Canonical {
+        kinds: ty.value.kinds.clone(),
         value: InEnvironment {
             value: Obligation::Trait(trait_ref),
             environment: ty.environment.clone(),
@@ -81,7 +81,7 @@ fn deref_by_trait(
 
     // Now do the assoc type projection
     let projection = super::traits::ProjectionPredicate {
-        ty: Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.num_vars)),
+        ty: Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.kinds.len())),
         projection_ty: super::ProjectionTy { associated_ty: target, parameters },
     };
 
@@ -89,7 +89,8 @@ fn deref_by_trait(
 
     let in_env = InEnvironment { value: obligation, environment: ty.environment };
 
-    let canonical = super::Canonical { num_vars: 1 + ty.value.num_vars, value: in_env };
+    let canonical =
+        Canonical::new(in_env, ty.value.kinds.iter().copied().chain(Some(super::TyKind::General)));
 
     let solution = db.trait_solve(krate, canonical)?;
 
@@ -110,7 +111,7 @@ fn deref_by_trait(
             // assumptions will be broken. We would need to properly introduce
             // new variables in that case
 
-            for i in 1..vars.0.num_vars {
+            for i in 1..vars.0.kinds.len() {
                 if vars.0.value[i - 1] != Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
                 {
                     warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.value, solution);
@@ -119,7 +120,7 @@ fn deref_by_trait(
             }
             Some(Canonical {
                 value: vars.0.value[vars.0.value.len() - 1].clone(),
-                num_vars: vars.0.num_vars,
+                kinds: vars.0.kinds.clone(),
             })
         }
         Solution::Ambig(_) => {
diff --git a/crates/ra_hir_ty/src/infer/unify.rs b/crates/ra_hir_ty/src/infer/unify.rs
index 269495ca0..2e895d911 100644
--- a/crates/ra_hir_ty/src/infer/unify.rs
+++ b/crates/ra_hir_ty/src/infer/unify.rs
@@ -9,7 +9,7 @@ use test_utils::mark;
 use super::{InferenceContext, Obligation};
 use crate::{
     BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferTy, Substs, Ty,
-    TypeCtor, TypeWalk,
+    TyKind, TypeCtor, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -86,10 +86,20 @@ where
     }
 
     fn into_canonicalized<T>(self, result: T) -> Canonicalized<T> {
-        Canonicalized {
-            value: Canonical { value: result, num_vars: self.free_vars.len() },
-            free_vars: self.free_vars,
-        }
+        let kinds = self
+            .free_vars
+            .iter()
+            .map(|v| match v {
+                // mapping MaybeNeverTypeVar to the same kind as general ones
+                // should be fine, because as opposed to int or float type vars,
+                // they don't restrict what kind of type can go into them, they
+                // just affect fallback.
+                InferTy::TypeVar(_) | InferTy::MaybeNeverTypeVar(_) => TyKind::General,
+                InferTy::IntVar(_) => TyKind::Integer,
+                InferTy::FloatVar(_) => TyKind::Float,
+            })
+            .collect();
+        Canonicalized { value: Canonical { value: result, kinds }, free_vars: self.free_vars }
     }
 
     pub(crate) fn canonicalize_ty(mut self, ty: Ty) -> Canonicalized<Ty> {
@@ -131,26 +141,41 @@ impl<T> Canonicalized<T> {
         ty
     }
 
-    pub fn apply_solution(&self, ctx: &mut InferenceContext<'_>, solution: Canonical<Vec<Ty>>) {
+    pub fn apply_solution(&self, ctx: &mut InferenceContext<'_>, solution: Canonical<Substs>) {
         // the solution may contain new variables, which we need to convert to new inference vars
-        let new_vars = Substs((0..solution.num_vars).map(|_| ctx.table.new_type_var()).collect());
+        let new_vars = Substs(
+            solution
+                .kinds
+                .iter()
+                .map(|k| match k {
+                    TyKind::General => ctx.table.new_type_var(),
+                    TyKind::Integer => ctx.table.new_integer_var(),
+                    TyKind::Float => ctx.table.new_float_var(),
+                })
+                .collect(),
+        );
         for (i, ty) in solution.value.into_iter().enumerate() {
             let var = self.free_vars[i];
             // eagerly replace projections in the type; we may be getting types
             // e.g. from where clauses where this hasn't happened yet
-            let ty = ctx.normalize_associated_types_in(ty.subst_bound_vars(&new_vars));
+            let ty = ctx.normalize_associated_types_in(ty.clone().subst_bound_vars(&new_vars));
             ctx.table.unify(&Ty::Infer(var), &ty);
         }
     }
 }
 
-pub fn unify(ty1: &Canonical<Ty>, ty2: &Canonical<Ty>) -> Option<Substs> {
+pub fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substs> {
     let mut table = InferenceTable::new();
-    let num_vars = ty1.num_vars.max(ty2.num_vars);
-    let vars =
-        Substs::builder(num_vars).fill(std::iter::repeat_with(|| table.new_type_var())).build();
-    let ty1_with_vars = ty1.value.clone().subst_bound_vars(&vars);
-    let ty2_with_vars = ty2.value.clone().subst_bound_vars(&vars);
+    let vars = Substs(
+        tys.kinds
+            .iter()
+            // we always use type vars here because we want everything to
+            // fallback to Unknown in the end (kind of hacky, as below)
+            .map(|_| table.new_type_var())
+            .collect(),
+    );
+    let ty1_with_vars = tys.value.0.clone().subst_bound_vars(&vars);
+    let ty2_with_vars = tys.value.1.clone().subst_bound_vars(&vars);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
         return None;
     }
@@ -162,7 +187,7 @@ pub fn unify(ty1: &Canonical<Ty>, ty2: &Canonical<Ty>) -> Option<Substs> {
         }
     }
     Some(
-        Substs::builder(ty1.num_vars)
+        Substs::builder(tys.kinds.len())
             .fill(vars.iter().map(|v| table.resolve_ty_completely(v.clone())))
             .build(),
     )
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index c9513b752..7f3f5e771 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -662,13 +662,27 @@ impl TypeWalk for GenericPredicate {
 
 /// Basically a claim (currently not validated / checked) that the contained
 /// type / trait ref contains no inference variables; any inference variables it
-/// contained have been replaced by bound variables, and `num_vars` tells us how
-/// many there are. This is used to erase irrelevant differences between types
-/// before using them in queries.
+/// contained have been replaced by bound variables, and `kinds` tells us how
+/// many there are and whether they were normal or float/int variables. This is
+/// used to erase irrelevant differences between types before using them in
+/// queries.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Canonical<T> {
     pub value: T,
-    pub num_vars: usize,
+    pub kinds: Arc<[TyKind]>,
+}
+
+impl<T> Canonical<T> {
+    pub fn new(value: T, kinds: impl IntoIterator<Item = TyKind>) -> Self {
+        Self { value, kinds: kinds.into_iter().collect() }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum TyKind {
+    General,
+    Integer,
+    Float,
 }
 
 /// A function signature as seen by type inference: Several parameter types and
diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index 5dbabd12b..a45febbf7 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -2,7 +2,7 @@
 //! For details about how this works in rustc, see the method lookup page in the
 //! [rustc guide](https://rust-lang.github.io/rustc-guide/method-lookup.html)
 //! and the corresponding code mostly in librustc_typeck/check/method/probe.rs.
-use std::sync::Arc;
+use std::{iter, sync::Arc};
 
 use arrayvec::ArrayVec;
 use hir_def::{
@@ -17,7 +17,8 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use super::Substs;
 use crate::{
     autoderef, db::HirDatabase, primitive::FloatBitness, utils::all_super_traits, ApplicationTy,
-    Canonical, DebruijnIndex, InEnvironment, TraitEnvironment, TraitRef, Ty, TypeCtor, TypeWalk,
+    Canonical, DebruijnIndex, InEnvironment, TraitEnvironment, TraitRef, Ty, TyKind, TypeCtor,
+    TypeWalk,
 };
 
 /// This is used as a key for indexing impls.
@@ -372,7 +373,7 @@ fn iterate_method_candidates_with_autoref(
         return true;
     }
     let refed = Canonical {
-        num_vars: deref_chain[0].num_vars,
+        kinds: deref_chain[0].kinds.clone(),
         value: Ty::apply_one(TypeCtor::Ref(Mutability::Shared), deref_chain[0].value.clone()),
     };
     if iterate_method_candidates_by_receiver(
@@ -388,7 +389,7 @@ fn iterate_method_candidates_with_autoref(
         return true;
     }
     let ref_muted = Canonical {
-        num_vars: deref_chain[0].num_vars,
+        kinds: deref_chain[0].kinds.clone(),
         value: Ty::apply_one(TypeCtor::Ref(Mutability::Mut), deref_chain[0].value.clone()),
     };
     if iterate_method_candidates_by_receiver(
@@ -607,18 +608,19 @@ pub(crate) fn inherent_impl_substs(
     // we create a var for each type parameter of the impl; we need to keep in
     // mind here that `self_ty` might have vars of its own
     let vars = Substs::build_for_def(db, impl_id)
-        .fill_with_bound_vars(DebruijnIndex::INNERMOST, self_ty.num_vars)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, self_ty.kinds.len())
         .build();
     let self_ty_with_vars = db.impl_self_ty(impl_id).subst(&vars);
-    let self_ty_with_vars =
-        Canonical { num_vars: vars.len() + self_ty.num_vars, value: self_ty_with_vars };
-    let substs = super::infer::unify(&self_ty_with_vars, self_ty);
+    let mut kinds = self_ty.kinds.to_vec();
+    kinds.extend(iter::repeat(TyKind::General).take(vars.len()));
+    let tys = Canonical { kinds: kinds.into(), value: (self_ty_with_vars, self_ty.value.clone()) };
+    let substs = super::infer::unify(&tys);
     // We only want the substs for the vars we added, not the ones from self_ty.
     // Also, if any of the vars we added are still in there, we replace them by
     // Unknown. I think this can only really happen if self_ty contained
     // Unknown, and in that case we want the result to contain Unknown in those
     // places again.
-    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.num_vars))
+    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.kinds.len()))
 }
 
 /// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
@@ -678,15 +680,15 @@ fn generic_implements_goal(
     trait_: TraitId,
     self_ty: Canonical<Ty>,
 ) -> Canonical<InEnvironment<super::Obligation>> {
-    let num_vars = self_ty.num_vars;
+    let mut kinds = self_ty.kinds.to_vec();
     let substs = super::Substs::build_for_def(db, trait_)
         .push(self_ty.value)
-        .fill_with_bound_vars(DebruijnIndex::INNERMOST, num_vars)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, kinds.len())
         .build();
-    let num_vars = substs.len() - 1 + self_ty.num_vars;
+    kinds.extend(iter::repeat(TyKind::General).take(substs.len() - 1));
     let trait_ref = TraitRef { trait_, substs };
     let obligation = super::Obligation::Trait(trait_ref);
-    Canonical { num_vars, value: InEnvironment::new(env, obligation) }
+    Canonical { kinds: kinds.into(), value: InEnvironment::new(env, obligation) }
 }
 
 fn autoderef_method_receiver(
@@ -699,9 +701,9 @@ fn autoderef_method_receiver(
     if let Some(Ty::Apply(ApplicationTy { ctor: TypeCtor::Array, parameters })) =
         deref_chain.last().map(|ty| &ty.value)
     {
-        let num_vars = deref_chain.last().unwrap().num_vars;
+        let kinds = deref_chain.last().unwrap().kinds.clone();
         let unsized_ty = Ty::apply(TypeCtor::Slice, parameters.clone());
-        deref_chain.push(Canonical { value: unsized_ty, num_vars })
+        deref_chain.push(Canonical { value: unsized_ty, kinds })
     }
     deref_chain
 }
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index 01c919a7e..766790576 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -3029,3 +3029,21 @@ fn infer_dyn_fn_output() {
     "###
     );
 }
+
+#[test]
+fn variable_kinds() {
+    check_types(
+        r#"
+trait Trait<T> { fn get(self, t: T) -> T; }
+struct S;
+impl Trait<u128> for S {}
+impl Trait<f32> for S {}
+fn test() {
+    S.get(1);
+  //^^^^^^^^ u128
+    S.get(1.);
+  //^^^^^^^^ f32
+}
+        "#,
+    );
+}
diff --git a/crates/ra_hir_ty/src/traits.rs b/crates/ra_hir_ty/src/traits.rs
index 6f43c3a22..2a6d7faef 100644
--- a/crates/ra_hir_ty/src/traits.rs
+++ b/crates/ra_hir_ty/src/traits.rs
@@ -1,5 +1,5 @@
 //! Trait solving using Chalk.
-use std::{panic, sync::Arc};
+use std::sync::Arc;
 
 use chalk_ir::cast::Cast;
 use hir_def::{
@@ -8,7 +8,7 @@ use hir_def::{
 use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 
-use crate::{db::HirDatabase, DebruijnIndex};
+use crate::{db::HirDatabase, DebruijnIndex, Substs};
 
 use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
 
@@ -190,15 +190,7 @@ fn solution_from_chalk(
     solution: chalk_solve::Solution<Interner>,
 ) -> Solution {
     let convert_subst = |subst: chalk_ir::Canonical<chalk_ir::Substitution<Interner>>| {
-        let value = subst
-            .value
-            .iter(&Interner)
-            .map(|p| match p.ty(&Interner) {
-                Some(ty) => from_chalk(db, ty.clone()),
-                None => unimplemented!(),
-            })
-            .collect();
-        let result = Canonical { value, num_vars: subst.binders.len(&Interner) };
+        let result = from_chalk(db, subst);
         SolutionVariables(result)
     };
     match solution {
@@ -222,7 +214,7 @@ fn solution_from_chalk(
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct SolutionVariables(pub Canonical<Vec<Ty>>);
+pub struct SolutionVariables(pub Canonical<Substs>);
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 /// A (possible) solution for a proposed goal.
diff --git a/crates/ra_hir_ty/src/traits/chalk/mapping.rs b/crates/ra_hir_ty/src/traits/chalk/mapping.rs
index ac82ea831..433d6aa03 100644
--- a/crates/ra_hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/ra_hir_ty/src/traits/chalk/mapping.rs
@@ -17,7 +17,7 @@ use crate::{
     primitive::{FloatBitness, FloatTy, IntBitness, IntTy, Signedness},
     traits::{builtin, AssocTyValue, Canonical, Impl, Obligation},
     ApplicationTy, CallableDef, GenericPredicate, InEnvironment, OpaqueTy, OpaqueTyId,
-    ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor,
+    ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeCtor,
 };
 
 use super::interner::*;
@@ -555,22 +555,39 @@ where
     type Chalk = chalk_ir::Canonical<T::Chalk>;
 
     fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Canonical<T::Chalk> {
-        let parameter = chalk_ir::CanonicalVarKind::new(
-            chalk_ir::VariableKind::Ty(chalk_ir::TyKind::General),
-            chalk_ir::UniverseIndex::ROOT,
-        );
+        let kinds = self
+            .kinds
+            .iter()
+            .map(|k| match k {
+                TyKind::General => chalk_ir::TyKind::General,
+                TyKind::Integer => chalk_ir::TyKind::Integer,
+                TyKind::Float => chalk_ir::TyKind::Float,
+            })
+            .map(|tk| {
+                chalk_ir::CanonicalVarKind::new(
+                    chalk_ir::VariableKind::Ty(tk),
+                    chalk_ir::UniverseIndex::ROOT,
+                )
+            });
         let value = self.value.to_chalk(db);
-        chalk_ir::Canonical {
-            value,
-            binders: chalk_ir::CanonicalVarKinds::from(&Interner, vec![parameter; self.num_vars]),
-        }
+        chalk_ir::Canonical { value, binders: chalk_ir::CanonicalVarKinds::from(&Interner, kinds) }
     }
 
     fn from_chalk(db: &dyn HirDatabase, canonical: chalk_ir::Canonical<T::Chalk>) -> Canonical<T> {
-        Canonical {
-            num_vars: canonical.binders.len(&Interner),
-            value: from_chalk(db, canonical.value),
-        }
+        let kinds = canonical
+            .binders
+            .iter(&Interner)
+            .map(|k| match k.kind {
+                chalk_ir::VariableKind::Ty(tk) => match tk {
+                    chalk_ir::TyKind::General => TyKind::General,
+                    chalk_ir::TyKind::Integer => TyKind::Integer,
+                    chalk_ir::TyKind::Float => TyKind::Float,
+                },
+                chalk_ir::VariableKind::Lifetime => panic!("unexpected lifetime from Chalk"),
+                chalk_ir::VariableKind::Const(_) => panic!("unexpected const from Chalk"),
+            })
+            .collect();
+        Canonical { kinds, value: from_chalk(db, canonical.value) }
     }
 }
 
diff --git a/crates/ra_ide/src/completion.rs b/crates/ra_ide/src/completion.rs
index 69ea754b3..9ebb8ebb7 100644
--- a/crates/ra_ide/src/completion.rs
+++ b/crates/ra_ide/src/completion.rs
@@ -63,11 +63,11 @@ pub use crate::completion::{
 // There also snippet completions:
 //
 // .Expressions
-// - `pd` -> `println!("{:?}")`
-// - `ppd` -> `println!("{:#?}")`
+// - `pd` -> `eprintln!(" = {:?}", );")`
+// - `ppd` -> `eprintln!(" = {:#?}", );`
 //
 // .Items
-// - `tfn` -> `#[test] fn f(){}`
+// - `tfn` -> `#[test] fn feature(){}`
 // - `tmod` ->
 // ```rust
 // #[cfg(test)]
@@ -75,7 +75,7 @@ pub use crate::completion::{
 //     use super::*;
 //
 //     #[test]
-//     fn test_fn() {}
+//     fn test_name() {}
 // }
 // ```
 
diff --git a/crates/ra_ide/src/completion/complete_keyword.rs b/crates/ra_ide/src/completion/complete_keyword.rs
index 3b174f916..e599cc3d1 100644
--- a/crates/ra_ide/src/completion/complete_keyword.rs
+++ b/crates/ra_ide/src/completion/complete_keyword.rs
@@ -1,6 +1,6 @@
 //! FIXME: write short doc here
 
-use ra_syntax::ast;
+use ra_syntax::{ast, SyntaxKind};
 
 use crate::completion::{
     CompletionContext, CompletionItem, CompletionItemKind, CompletionKind, Completions,
@@ -37,6 +37,10 @@ pub(super) fn complete_use_tree_keyword(acc: &mut Completions, ctx: &CompletionC
 }
 
 pub(super) fn complete_expr_keyword(acc: &mut Completions, ctx: &CompletionContext) {
+    if ctx.token.kind() == SyntaxKind::COMMENT {
+        return;
+    }
+
     let has_trait_or_impl_parent = ctx.has_impl_parent || ctx.has_trait_parent;
     if ctx.trait_as_prev_sibling || ctx.impl_as_prev_sibling {
         add_keyword(ctx, acc, "where", "where ");
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index 4fdc2f0bb..b18279746 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -1516,4 +1516,54 @@ mod tests {
         "###
         );
     }
+
+    #[test]
+    fn no_keyword_autocompletion_on_line_comments() {
+        assert_debug_snapshot!(
+        do_completion(
+                r"
+                    fn test() {
+                        let x = 2; // A comment<|>
+                    }
+                    ",
+                CompletionKind::Keyword
+        ),
+            @r###"
+            []
+            "###
+        );
+    }
+
+    #[test]
+    fn no_keyword_autocompletion_on_multi_line_comments() {
+        assert_debug_snapshot!(
+        do_completion(
+                r"
+                    /*
+                    Some multi-line comment<|>
+                    */
+                    ",
+                CompletionKind::Keyword
+        ),
+            @r###"
+            []
+            "###
+        );
+    }
+
+    #[test]
+    fn no_keyword_autocompletion_on_doc_comments() {
+        assert_debug_snapshot!(
+        do_completion(
+                r"
+                    /// Some doc comment
+                    /// let test<|> = 1
+                    ",
+                CompletionKind::Keyword
+        ),
+            @r###"
+            []
+            "###
+        );
+    }
 }
diff --git a/crates/ra_ide/src/ssr.rs b/crates/ra_ide/src/ssr.rs
index 9f8e540c0..b3e9e5dfe 100644
--- a/crates/ra_ide/src/ssr.rs
+++ b/crates/ra_ide/src/ssr.rs
@@ -10,6 +10,18 @@ use ra_ssr::{MatchFinder, SsrError, SsrRule};
 // The syntax for a structural search replace command is `<search_pattern> ==>> <replace_pattern>`.
 // A `$<name>` placeholder in the search pattern will match any AST node and `$<name>` will reference it in the replacement.
 // Within a macro call, a placeholder will match up until whatever token follows the placeholder.
+//
+// Placeholders may be given constraints by writing them as `${<name>:<constraint1>:<constraint2>...}`.
+//
+// Supported constraints:
+//
+// |===
+// | Constraint    | Restricts placeholder
+//
+// | kind(literal) | Is a literal (e.g. `42` or `"forty two"`)
+// | not(a)        | Negates the constraint `a`
+// |===
+//
 // Available via the command `rust-analyzer.ssr`.
 //
 // ```rust
diff --git a/crates/ra_ssr/Cargo.toml b/crates/ra_ssr/Cargo.toml
index 3c2f15a83..fe098aaee 100644
--- a/crates/ra_ssr/Cargo.toml
+++ b/crates/ra_ssr/Cargo.toml
@@ -17,3 +17,4 @@ ra_db = { path = "../ra_db" }
 ra_ide_db = { path = "../ra_ide_db" }
 hir = { path = "../ra_hir", package = "ra_hir" }
 rustc-hash = "1.1.0"
+test_utils = { path = "../test_utils" }
diff --git a/crates/ra_ssr/src/matching.rs b/crates/ra_ssr/src/matching.rs
index 53d802e77..ce53d46d2 100644
--- a/crates/ra_ssr/src/matching.rs
+++ b/crates/ra_ssr/src/matching.rs
@@ -2,7 +2,7 @@
 //! process of matching, placeholder values are recorded.
 
 use crate::{
-    parsing::{Placeholder, SsrTemplate},
+    parsing::{Constraint, NodeKind, Placeholder, SsrTemplate},
     SsrMatches, SsrPattern, SsrRule,
 };
 use hir::Semantics;
@@ -11,6 +11,7 @@ use ra_syntax::ast::{AstNode, AstToken};
 use ra_syntax::{ast, SyntaxElement, SyntaxElementChildren, SyntaxKind, SyntaxNode, SyntaxToken};
 use rustc_hash::FxHashMap;
 use std::{cell::Cell, iter::Peekable};
+use test_utils::mark;
 
 // Creates a match error. If we're currently attempting to match some code that we thought we were
 // going to match, as indicated by the --debug-snippet flag, then populate the reason field.
@@ -169,6 +170,9 @@ impl<'db, 'sema> MatchState<'db, 'sema> {
         if let Some(placeholder) =
             match_inputs.get_placeholder(&SyntaxElement::Node(pattern.clone()))
         {
+            for constraint in &placeholder.constraints {
+                self.check_constraint(constraint, code)?;
+            }
             if self.match_out.is_none() {
                 return Ok(());
             }
@@ -292,6 +296,24 @@ impl<'db, 'sema> MatchState<'db, 'sema> {
         Ok(())
     }
 
+    fn check_constraint(
+        &self,
+        constraint: &Constraint,
+        code: &SyntaxNode,
+    ) -> Result<(), MatchFailed> {
+        match constraint {
+            Constraint::Kind(kind) => {
+                kind.matches(code)?;
+            }
+            Constraint::Not(sub) => {
+                if self.check_constraint(&*sub, code).is_ok() {
+                    fail_match!("Constraint {:?} failed for '{}'", constraint, code.text());
+                }
+            }
+        }
+        Ok(())
+    }
+
     /// We want to allow the records to match in any order, so we have special matching logic for
     /// them.
     fn attempt_match_record_field_list(
@@ -515,6 +537,21 @@ impl SsrPattern {
     }
 }
 
+impl NodeKind {
+    fn matches(&self, node: &SyntaxNode) -> Result<(), MatchFailed> {
+        let ok = match self {
+            Self::Literal => {
+                mark::hit!(literal_constraint);
+                ast::Literal::can_cast(node.kind())
+            }
+        };
+        if !ok {
+            fail_match!("Code '{}' isn't of kind {:?}", node.text(), self);
+        }
+        Ok(())
+    }
+}
+
 // If `node` contains nothing but an ident then return it, otherwise return None.
 fn only_ident(element: SyntaxElement) -> Option<SyntaxToken> {
     match element {
diff --git a/crates/ra_ssr/src/parsing.rs b/crates/ra_ssr/src/parsing.rs
index 04d46bd32..5ea125616 100644
--- a/crates/ra_ssr/src/parsing.rs
+++ b/crates/ra_ssr/src/parsing.rs
@@ -6,7 +6,7 @@
 //! e.g. expressions, type references etc.
 
 use crate::{SsrError, SsrPattern, SsrRule};
-use ra_syntax::{ast, AstNode, SmolStr, SyntaxKind};
+use ra_syntax::{ast, AstNode, SmolStr, SyntaxKind, T};
 use rustc_hash::{FxHashMap, FxHashSet};
 use std::str::FromStr;
 
@@ -39,6 +39,18 @@ pub(crate) struct Placeholder {
     pub(crate) ident: SmolStr,
     /// A unique name used in place of this placeholder when we parse the pattern as Rust code.
     stand_in_name: String,
+    pub(crate) constraints: Vec<Constraint>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) enum Constraint {
+    Kind(NodeKind),
+    Not(Box<Constraint>),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) enum NodeKind {
+    Literal,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -149,7 +161,7 @@ fn parse_pattern(pattern_str: &str) -> Result<Vec<PatternElement>, SsrError> {
     let mut placeholder_names = FxHashSet::default();
     let mut tokens = tokenize(pattern_str)?.into_iter();
     while let Some(token) = tokens.next() {
-        if token.kind == SyntaxKind::DOLLAR {
+        if token.kind == T![$] {
             let placeholder = parse_placeholder(&mut tokens)?;
             if !placeholder_names.insert(placeholder.ident.clone()) {
                 bail!("Name `{}` repeats more than once", placeholder.ident);
@@ -177,6 +189,9 @@ fn validate_rule(rule: &SsrRule) -> Result<(), SsrError> {
             if !defined_placeholders.contains(&placeholder.ident) {
                 undefined.push(format!("${}", placeholder.ident));
             }
+            if !placeholder.constraints.is_empty() {
+                bail!("Replacement placeholders cannot have constraints");
+            }
         }
     }
     if !undefined.is_empty() {
@@ -205,23 +220,90 @@ fn tokenize(source: &str) -> Result<Vec<Token>, SsrError> {
 
 fn parse_placeholder(tokens: &mut std::vec::IntoIter<Token>) -> Result<Placeholder, SsrError> {
     let mut name = None;
+    let mut constraints = Vec::new();
     if let Some(token) = tokens.next() {
         match token.kind {
             SyntaxKind::IDENT => {
                 name = Some(token.text);
             }
+            T!['{'] => {
+                let token =
+                    tokens.next().ok_or_else(|| SsrError::new("Unexpected end of placeholder"))?;
+                if token.kind == SyntaxKind::IDENT {
+                    name = Some(token.text);
+                }
+                loop {
+                    let token = tokens
+                        .next()
+                        .ok_or_else(|| SsrError::new("Placeholder is missing closing brace '}'"))?;
+                    match token.kind {
+                        T![:] => {
+                            constraints.push(parse_constraint(tokens)?);
+                        }
+                        T!['}'] => break,
+                        _ => bail!("Unexpected token while parsing placeholder: '{}'", token.text),
+                    }
+                }
+            }
             _ => {
-                bail!("Placeholders should be $name");
+                bail!("Placeholders should either be $name or ${name:constraints}");
             }
         }
     }
     let name = name.ok_or_else(|| SsrError::new("Placeholder ($) with no name"))?;
-    Ok(Placeholder::new(name))
+    Ok(Placeholder::new(name, constraints))
+}
+
+fn parse_constraint(tokens: &mut std::vec::IntoIter<Token>) -> Result<Constraint, SsrError> {
+    let constraint_type = tokens
+        .next()
+        .ok_or_else(|| SsrError::new("Found end of placeholder while looking for a constraint"))?
+        .text
+        .to_string();
+    match constraint_type.as_str() {
+        "kind" => {
+            expect_token(tokens, "(")?;
+            let t = tokens.next().ok_or_else(|| {
+                SsrError::new("Unexpected end of constraint while looking for kind")
+            })?;
+            if t.kind != SyntaxKind::IDENT {
+                bail!("Expected ident, found {:?} while parsing kind constraint", t.kind);
+            }
+            expect_token(tokens, ")")?;
+            Ok(Constraint::Kind(NodeKind::from(&t.text)?))
+        }
+        "not" => {
+            expect_token(tokens, "(")?;
+            let sub = parse_constraint(tokens)?;
+            expect_token(tokens, ")")?;
+            Ok(Constraint::Not(Box::new(sub)))
+        }
+        x => bail!("Unsupported constraint type '{}'", x),
+    }
+}
+
+fn expect_token(tokens: &mut std::vec::IntoIter<Token>, expected: &str) -> Result<(), SsrError> {
+    if let Some(t) = tokens.next() {
+        if t.text == expected {
+            return Ok(());
+        }
+        bail!("Expected {} found {}", expected, t.text);
+    }
+    bail!("Expected {} found end of stream");
+}
+
+impl NodeKind {
+    fn from(name: &SmolStr) -> Result<NodeKind, SsrError> {
+        Ok(match name.as_str() {
+            "literal" => NodeKind::Literal,
+            _ => bail!("Unknown node kind '{}'", name),
+        })
+    }
 }
 
 impl Placeholder {
-    fn new(name: SmolStr) -> Self {
-        Self { stand_in_name: format!("__placeholder_{}", name), ident: name }
+    fn new(name: SmolStr, constraints: Vec<Constraint>) -> Self {
+        Self { stand_in_name: format!("__placeholder_{}", name), constraints, ident: name }
     }
 }
 
@@ -241,31 +323,31 @@ mod tests {
             PatternElement::Token(Token { kind, text: SmolStr::new(text) })
         }
         fn placeholder(name: &str) -> PatternElement {
-            PatternElement::Placeholder(Placeholder::new(SmolStr::new(name)))
+            PatternElement::Placeholder(Placeholder::new(SmolStr::new(name), Vec::new()))
         }
         let result: SsrRule = "foo($a, $b) ==>> bar($b, $a)".parse().unwrap();
         assert_eq!(
             result.pattern.raw.tokens,
             vec![
                 token(SyntaxKind::IDENT, "foo"),
-                token(SyntaxKind::L_PAREN, "("),
+                token(T!['('], "("),
                 placeholder("a"),
-                token(SyntaxKind::COMMA, ","),
+                token(T![,], ","),
                 token(SyntaxKind::WHITESPACE, " "),
                 placeholder("b"),
-                token(SyntaxKind::R_PAREN, ")"),
+                token(T![')'], ")"),
             ]
         );
         assert_eq!(
             result.template.tokens,
             vec![
                 token(SyntaxKind::IDENT, "bar"),
-                token(SyntaxKind::L_PAREN, "("),
+                token(T!['('], "("),
                 placeholder("b"),
-                token(SyntaxKind::COMMA, ","),
+                token(T![,], ","),
                 token(SyntaxKind::WHITESPACE, " "),
                 placeholder("a"),
-                token(SyntaxKind::R_PAREN, ")"),
+                token(T![')'], ")"),
             ]
         );
     }
diff --git a/crates/ra_ssr/src/tests.rs b/crates/ra_ssr/src/tests.rs
index c692c97e2..9568d4432 100644
--- a/crates/ra_ssr/src/tests.rs
+++ b/crates/ra_ssr/src/tests.rs
@@ -1,5 +1,6 @@
 use crate::{MatchFinder, SsrRule};
 use ra_db::{FileId, SourceDatabaseExt};
+use test_utils::mark;
 
 fn parse_error_text(query: &str) -> String {
     format!("{}", query.parse::<SsrRule>().unwrap_err())
@@ -302,6 +303,22 @@ fn match_pattern() {
 }
 
 #[test]
+fn literal_constraint() {
+    mark::check!(literal_constraint);
+    let code = r#"
+        fn f1() {
+            let x1 = Some(42);
+            let x2 = Some("foo");
+            let x3 = Some(x1);
+            let x4 = Some(40 + 2);
+            let x5 = Some(true);
+        }
+        "#;
+    assert_matches("Some(${a:kind(literal)})", code, &["Some(42)", "Some(\"foo\")", "Some(true)"]);
+    assert_matches("Some(${a:not(kind(literal))})", code, &["Some(x1)", "Some(40 + 2)"]);
+}
+
+#[test]
 fn match_reordered_struct_instantiation() {
     assert_matches(
         "Foo {aa: 1, b: 2, ccc: 3}",