diff --git a/Cargo.lock b/Cargo.lock
index 92d5edea6f..9acace2fb3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1855,7 +1855,9 @@ dependencies = [
 name = "span"
 version = "0.0.0"
 dependencies = [
+ "hashbrown",
  "la-arena 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-hash",
  "salsa",
  "stdx",
  "syntax",
diff --git a/crates/hir-def/src/body/lower.rs b/crates/hir-def/src/body/lower.rs
index 5dc5fedd23..ad8782d3d1 100644
--- a/crates/hir-def/src/body/lower.rs
+++ b/crates/hir-def/src/body/lower.rs
@@ -6,7 +6,6 @@ use std::mem;
 use base_db::CrateId;
 use either::Either;
 use hir_expand::{
-    ast_id_map::AstIdMap,
     name::{name, AsName, Name},
     ExpandError, InFile,
 };
@@ -14,6 +13,7 @@ use intern::Interned;
 use profile::Count;
 use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
+use span::AstIdMap;
 use syntax::{
     ast::{
         self, ArrayExprKind, AstChildren, BlockExpr, HasArgList, HasAttrs, HasLoopBody, HasName,
diff --git a/crates/hir-def/src/item_tree.rs b/crates/hir-def/src/item_tree.rs
index bb36950f95..c7cf611589 100644
--- a/crates/hir-def/src/item_tree.rs
+++ b/crates/hir-def/src/item_tree.rs
@@ -47,18 +47,13 @@ use std::{
 use ast::{AstNode, StructKind};
 use base_db::CrateId;
 use either::Either;
-use hir_expand::{
-    ast_id_map::{AstIdNode, FileAstId},
-    attrs::RawAttrs,
-    name::Name,
-    ExpandTo, HirFileId, InFile,
-};
+use hir_expand::{attrs::RawAttrs, name::Name, ExpandTo, HirFileId, InFile};
 use intern::Interned;
 use la_arena::{Arena, Idx, IdxRange, RawIdx};
 use profile::Count;
 use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
-use span::Span;
+use span::{AstIdNode, FileAstId, Span};
 use stdx::never;
 use syntax::{ast, match_ast, SyntaxKind};
 use triomphe::Arc;
diff --git a/crates/hir-def/src/item_tree/lower.rs b/crates/hir-def/src/item_tree/lower.rs
index 37fdece876..21cffafa95 100644
--- a/crates/hir-def/src/item_tree/lower.rs
+++ b/crates/hir-def/src/item_tree/lower.rs
@@ -2,10 +2,9 @@
 
 use std::collections::hash_map::Entry;
 
-use hir_expand::{
-    ast_id_map::AstIdMap, mod_path::path, name, name::AsName, span_map::SpanMapRef, HirFileId,
-};
+use hir_expand::{mod_path::path, name, name::AsName, span_map::SpanMapRef, HirFileId};
 use la_arena::Arena;
+use span::AstIdMap;
 use syntax::{
     ast::{self, HasModuleItem, HasName, HasTypeBounds, IsString},
     AstNode,
diff --git a/crates/hir-def/src/lib.rs b/crates/hir-def/src/lib.rs
index 5670ebfa17..de3ab57a12 100644
--- a/crates/hir-def/src/lib.rs
+++ b/crates/hir-def/src/lib.rs
@@ -76,7 +76,6 @@ use base_db::{
     CrateId, Edition,
 };
 use hir_expand::{
-    ast_id_map::{AstIdNode, FileAstId},
     builtin_attr_macro::BuiltinAttrExpander,
     builtin_derive_macro::BuiltinDeriveExpander,
     builtin_fn_macro::{BuiltinFnLikeExpander, EagerExpander},
@@ -91,7 +90,7 @@ use hir_expand::{
 use item_tree::ExternBlock;
 use la_arena::Idx;
 use nameres::DefMap;
-use span::{FileId, Span};
+use span::{AstIdNode, FileAstId, FileId, Span};
 use stdx::impl_from;
 use syntax::{ast, AstNode};
 
diff --git a/crates/hir-def/src/lower.rs b/crates/hir-def/src/lower.rs
index 395b69d284..2fa6acdf17 100644
--- a/crates/hir-def/src/lower.rs
+++ b/crates/hir-def/src/lower.rs
@@ -2,10 +2,10 @@
 use std::cell::OnceCell;
 
 use hir_expand::{
-    ast_id_map::{AstIdMap, AstIdNode},
     span_map::{SpanMap, SpanMapRef},
     AstId, HirFileId, InFile,
 };
+use span::{AstIdMap, AstIdNode};
 use syntax::ast;
 use triomphe::Arc;
 
diff --git a/crates/hir-def/src/nameres.rs b/crates/hir-def/src/nameres.rs
index 1a82782115..270468ad0a 100644
--- a/crates/hir-def/src/nameres.rs
+++ b/crates/hir-def/src/nameres.rs
@@ -61,13 +61,13 @@ use std::ops::Deref;
 
 use base_db::{CrateId, Edition, FileId};
 use hir_expand::{
-    ast_id_map::FileAstId, name::Name, proc_macro::ProcMacroKind, HirFileId, InFile, MacroCallId,
-    MacroDefId,
+    name::Name, proc_macro::ProcMacroKind, HirFileId, InFile, MacroCallId, MacroDefId,
 };
 use itertools::Itertools;
 use la_arena::Arena;
 use profile::Count;
 use rustc_hash::{FxHashMap, FxHashSet};
+use span::FileAstId;
 use stdx::format_to;
 use syntax::{ast, SmolStr};
 use triomphe::Arc;
diff --git a/crates/hir-def/src/nameres/collector.rs b/crates/hir-def/src/nameres/collector.rs
index 3282540650..538e735688 100644
--- a/crates/hir-def/src/nameres/collector.rs
+++ b/crates/hir-def/src/nameres/collector.rs
@@ -9,7 +9,6 @@ use base_db::{CrateId, Dependency, Edition, FileId};
 use cfg::{CfgExpr, CfgOptions};
 use either::Either;
 use hir_expand::{
-    ast_id_map::FileAstId,
     attrs::{Attr, AttrId},
     builtin_attr_macro::{find_builtin_attr, BuiltinAttrExpander},
     builtin_derive_macro::find_builtin_derive,
@@ -23,7 +22,7 @@ use itertools::{izip, Itertools};
 use la_arena::Idx;
 use limit::Limit;
 use rustc_hash::{FxHashMap, FxHashSet};
-use span::{ErasedFileAstId, Span, SyntaxContextId};
+use span::{ErasedFileAstId, FileAstId, Span, SyntaxContextId};
 use stdx::always;
 use syntax::{ast, SmolStr};
 use triomphe::Arc;
diff --git a/crates/hir-expand/src/db.rs b/crates/hir-expand/src/db.rs
index 6aea676459..f1f0d8990f 100644
--- a/crates/hir-expand/src/db.rs
+++ b/crates/hir-expand/src/db.rs
@@ -5,7 +5,7 @@ use either::Either;
 use limit::Limit;
 use mbe::{syntax_node_to_token_tree, ValueResult};
 use rustc_hash::FxHashSet;
-use span::{SyntaxContextData, SyntaxContextId};
+use span::{AstIdMap, SyntaxContextData, SyntaxContextId};
 use syntax::{
     ast::{self, HasAttrs},
     AstNode, Parse, SyntaxError, SyntaxNode, SyntaxToken, T,
@@ -13,7 +13,6 @@ use syntax::{
 use triomphe::Arc;
 
 use crate::{
-    ast_id_map::AstIdMap,
     attrs::collect_attrs,
     builtin_attr_macro::pseudo_derive_attr_expansion,
     builtin_fn_macro::EagerExpander,
@@ -58,7 +57,6 @@ pub trait ExpandDatabase: SourceDatabase {
     #[salsa::input]
     fn proc_macros(&self) -> Arc<ProcMacros>;
 
-    #[salsa::invoke(AstIdMap::new)]
     fn ast_id_map(&self, file_id: HirFileId) -> Arc<AstIdMap>;
 
     /// Main public API -- parses a hir file, not caring whether it's a real
@@ -253,6 +251,10 @@ pub fn expand_speculative(
     Some((node.syntax_node(), token))
 }
 
+fn ast_id_map(db: &dyn ExpandDatabase, file_id: span::HirFileId) -> triomphe::Arc<AstIdMap> {
+    triomphe::Arc::new(AstIdMap::from_source(&db.parse_or_expand(file_id)))
+}
+
 fn parse_or_expand(db: &dyn ExpandDatabase, file_id: HirFileId) -> SyntaxNode {
     match file_id.repr() {
         HirFileIdRepr::FileId(file_id) => db.parse(file_id).syntax_node(),
diff --git a/crates/hir-expand/src/files.rs b/crates/hir-expand/src/files.rs
index 707daf0402..66ceb1b7d4 100644
--- a/crates/hir-expand/src/files.rs
+++ b/crates/hir-expand/src/files.rs
@@ -2,10 +2,16 @@
 use std::iter;
 
 use either::Either;
-use span::{FileId, FileRange, HirFileId, HirFileIdRepr, MacroFileId, SyntaxContextId};
-use syntax::{AstNode, SyntaxNode, SyntaxToken, TextRange, TextSize};
+use span::{
+    AstIdNode, ErasedFileAstId, FileAstId, FileId, FileRange, HirFileId, HirFileIdRepr,
+    MacroFileId, SyntaxContextId,
+};
+use syntax::{AstNode, AstPtr, SyntaxNode, SyntaxNodePtr, SyntaxToken, TextRange, TextSize};
 
-use crate::{db, map_node_range_up, span_for_offset, MacroFileIdExt};
+use crate::{
+    db::{self, ExpandDatabase},
+    map_node_range_up, span_for_offset, MacroFileIdExt,
+};
 
 /// `InFile<T>` stores a value of `T` inside a particular file/syntax tree.
 ///
@@ -23,6 +29,31 @@ pub type InFile<T> = InFileWrapper<HirFileId, T>;
 pub type InMacroFile<T> = InFileWrapper<MacroFileId, T>;
 pub type InRealFile<T> = InFileWrapper<FileId, T>;
 
+/// `AstId` points to an AST node in any file.
+///
+/// It is stable across reparses, and can be used as salsa key/value.
+pub type AstId<N> = crate::InFile<FileAstId<N>>;
+
+impl<N: AstIdNode> AstId<N> {
+    pub fn to_node(&self, db: &dyn ExpandDatabase) -> N {
+        self.to_ptr(db).to_node(&db.parse_or_expand(self.file_id))
+    }
+    pub fn to_in_file_node(&self, db: &dyn ExpandDatabase) -> crate::InFile<N> {
+        crate::InFile::new(self.file_id, self.to_ptr(db).to_node(&db.parse_or_expand(self.file_id)))
+    }
+    pub fn to_ptr(&self, db: &dyn ExpandDatabase) -> AstPtr<N> {
+        db.ast_id_map(self.file_id).get(self.value)
+    }
+}
+
+pub type ErasedAstId = crate::InFile<ErasedFileAstId>;
+
+impl ErasedAstId {
+    pub fn to_ptr(&self, db: &dyn ExpandDatabase) -> SyntaxNodePtr {
+        db.ast_id_map(self.file_id).get_erased(self.value)
+    }
+}
+
 impl<FileKind, T> InFileWrapper<FileKind, T> {
     pub fn new(file_id: FileKind, value: T) -> Self {
         Self { file_id, value }
diff --git a/crates/hir-expand/src/lib.rs b/crates/hir-expand/src/lib.rs
index e1a79e8b58..42dc8c12d6 100644
--- a/crates/hir-expand/src/lib.rs
+++ b/crates/hir-expand/src/lib.rs
@@ -6,7 +6,6 @@
 
 #![warn(rust_2018_idioms, unused_lifetimes)]
 
-pub mod ast_id_map;
 pub mod attrs;
 pub mod builtin_attr_macro;
 pub mod builtin_derive_macro;
@@ -32,7 +31,7 @@ use std::{fmt, hash::Hash};
 
 use base_db::{salsa::impl_intern_value_trivial, CrateId, Edition, FileId};
 use either::Either;
-use span::{FileRange, HirFileIdRepr, Span, SyntaxContextData, SyntaxContextId};
+use span::{ErasedFileAstId, FileRange, HirFileIdRepr, Span, SyntaxContextData, SyntaxContextId};
 use syntax::{
     ast::{self, AstNode},
     SyntaxNode, SyntaxToken, TextRange, TextSize,
@@ -49,8 +48,7 @@ use crate::{
     span_map::{ExpansionSpanMap, SpanMap},
 };
 
-pub use crate::ast_id_map::{AstId, ErasedAstId, ErasedFileAstId};
-pub use crate::files::{InFile, InMacroFile, InRealFile};
+pub use crate::files::{AstId, ErasedAstId, InFile, InMacroFile, InRealFile};
 
 pub use mbe::ValueResult;
 pub use span::{HirFileId, MacroCallId, MacroFileId};
diff --git a/crates/span/Cargo.toml b/crates/span/Cargo.toml
index 7093f3a691..cbda91f0a5 100644
--- a/crates/span/Cargo.toml
+++ b/crates/span/Cargo.toml
@@ -12,7 +12,8 @@ authors.workspace = true
 [dependencies]
 la-arena.workspace = true
 salsa.workspace = true
-
+rustc-hash.workspace = true
+hashbrown.workspace = true
 
 # local deps
 vfs.workspace = true
diff --git a/crates/hir-expand/src/ast_id_map.rs b/crates/span/src/ast_id.rs
similarity index 85%
rename from crates/hir-expand/src/ast_id_map.rs
rename to crates/span/src/ast_id.rs
index ab582741f5..2d98aa81e5 100644
--- a/crates/hir-expand/src/ast_id_map.rs
+++ b/crates/span/src/ast_id.rs
@@ -5,8 +5,6 @@
 //! item as an ID. That way, id's don't change unless the set of items itself
 //! changes.
 
-// FIXME: Consider moving this into the span crate
-
 use std::{
     any::type_name,
     fmt,
@@ -15,38 +13,12 @@ use std::{
 };
 
 use la_arena::{Arena, Idx, RawIdx};
-use profile::Count;
 use rustc_hash::FxHasher;
 use syntax::{ast, AstNode, AstPtr, SyntaxNode, SyntaxNodePtr};
 
-use crate::db::ExpandDatabase;
-
-pub use span::ErasedFileAstId;
-
-/// `AstId` points to an AST node in any file.
-///
-/// It is stable across reparses, and can be used as salsa key/value.
-pub type AstId<N> = crate::InFile<FileAstId<N>>;
-
-impl<N: AstIdNode> AstId<N> {
-    pub fn to_node(&self, db: &dyn ExpandDatabase) -> N {
-        self.to_ptr(db).to_node(&db.parse_or_expand(self.file_id))
-    }
-    pub fn to_in_file_node(&self, db: &dyn ExpandDatabase) -> crate::InFile<N> {
-        crate::InFile::new(self.file_id, self.to_ptr(db).to_node(&db.parse_or_expand(self.file_id)))
-    }
-    pub fn to_ptr(&self, db: &dyn ExpandDatabase) -> AstPtr<N> {
-        db.ast_id_map(self.file_id).get(self.value)
-    }
-}
-
-pub type ErasedAstId = crate::InFile<ErasedFileAstId>;
-
-impl ErasedAstId {
-    pub fn to_ptr(&self, db: &dyn ExpandDatabase) -> SyntaxNodePtr {
-        db.ast_id_map(self.file_id).get_erased(self.value)
-    }
-}
+/// See crates\hir-expand\src\ast_id_map.rs
+/// This is a type erased FileAstId.
+pub type ErasedFileAstId = la_arena::Idx<syntax::SyntaxNodePtr>;
 
 /// `AstId` points to an AST node in a specific file.
 pub struct FileAstId<N: AstIdNode> {
@@ -138,7 +110,6 @@ pub struct AstIdMap {
     arena: Arena<SyntaxNodePtr>,
     /// Reverse: map ptr to id.
     map: hashbrown::HashMap<Idx<SyntaxNodePtr>, (), ()>,
-    _c: Count<Self>,
 }
 
 impl fmt::Debug for AstIdMap {
@@ -155,14 +126,7 @@ impl PartialEq for AstIdMap {
 impl Eq for AstIdMap {}
 
 impl AstIdMap {
-    pub(crate) fn new(
-        db: &dyn ExpandDatabase,
-        file_id: span::HirFileId,
-    ) -> triomphe::Arc<AstIdMap> {
-        triomphe::Arc::new(AstIdMap::from_source(&db.parse_or_expand(file_id)))
-    }
-
-    fn from_source(node: &SyntaxNode) -> AstIdMap {
+    pub fn from_source(node: &SyntaxNode) -> AstIdMap {
         assert!(node.parent().is_none());
         let mut res = AstIdMap::default();
 
diff --git a/crates/span/src/lib.rs b/crates/span/src/lib.rs
index 6b363e9050..0fe3275863 100644
--- a/crates/span/src/lib.rs
+++ b/crates/span/src/lib.rs
@@ -3,10 +3,12 @@ use std::fmt::{self, Write};
 
 use salsa::InternId;
 
+mod ast_id;
 mod hygiene;
 mod map;
 
 pub use self::{
+    ast_id::{AstIdMap, AstIdNode, ErasedFileAstId, FileAstId},
     hygiene::{SyntaxContextData, SyntaxContextId, Transparency},
     map::{RealSpanMap, SpanMap},
 };
@@ -26,10 +28,6 @@ pub struct FileRange {
     pub range: TextRange,
 }
 
-/// See crates\hir-expand\src\ast_id_map.rs
-/// This is a type erased FileAstId.
-pub type ErasedFileAstId = la_arena::Idx<syntax::SyntaxNodePtr>;
-
 // The first index is always the root node's AstId
 /// The root ast id always points to the encompassing file, using this in spans is discouraged as
 /// any range relative to it will be effectively absolute, ruining the entire point of anchored