skip generated symbols when looking for an ident

compiler/can/src/scope.rs

@@ -175,8 +175,8 @@ impl Scope {
     fn scope_contains_ident(&self, ident: &Ident) -> ContainsIdent {
         let result = self.locals.contains_ident(ident);
         match result {
-            ContainsIdent::InScope(symbol, region) => result,
+            ContainsIdent::InScope(_, _) => result,
-            ContainsIdent::NotInScope(ident_id) => match self.has_imported(ident) {
+            ContainsIdent::NotInScope(_) => match self.has_imported(ident) {
                 Some((symbol, region)) => ContainsIdent::InScope(symbol, region),
                 None => result,
             },
@@ -217,18 +217,27 @@ impl Scope {
         ident: &Ident,
         region: Region,
     ) -> Result<Symbol, (Region, Loc<Ident>)> {
-        let x = self.scope_contains_ident(ident);
+        match self.introduce_help(ident, region) {
-        if !self.home.is_builtin() {
+            Err((_, original_region)) => {
-            dbg!(ident, &x);
-        }
-        match x {
-            ContainsIdent::InScope(_, original_region) => {
                 let shadow = Loc {
                     value: ident.clone(),
                     region,
                 };
                 Err((original_region, shadow))
             }
+            Ok(symbol) => Ok(symbol),
+        }
+    }
+
+    fn introduce_help(
+        &mut self,
+        ident: &Ident,
+        region: Region,
+    ) -> Result<Symbol, (Symbol, Region)> {
+        match self.scope_contains_ident(ident) {
+            ContainsIdent::InScope(original_symbol, original_region) => {
+                Err((original_symbol, original_region))
+            }
             ContainsIdent::NotPresent => {
                 let ident_id = self.locals.introduce_into_scope(ident, region);
                 Ok(Symbol::new(self.home, ident_id))
@@ -266,8 +275,8 @@ impl Scope {
     ) -> Result<(Symbol, Option<Symbol>), (Region, Loc<Ident>, Symbol)> {
         let ident = &ident;
 
-        match self.scope_contains_ident(ident) {
+        match self.introduce_help(ident, region) {
-            ContainsIdent::InScope(original_symbol, original_region) => {
+            Err((original_symbol, original_region)) => {
                 let shadow_symbol = self.scopeless_symbol(ident, region);
 
                 if self.abilities_store.is_ability_member_name(original_symbol) {
@@ -285,26 +294,7 @@ impl Scope {
                     Err((original_region, shadow, shadow_symbol))
                 }
             }
-            ContainsIdent::NotPresent => {
+            Ok(symbol) => Ok((symbol, None)),
-                let ident_id = self.locals.introduce_into_scope(ident, region);
-                Ok((Symbol::new(self.home, ident_id), None))
-            }
-            ContainsIdent::NotInScope(existing) => {
-                if existing.index() < self.exposed_ident_count {
-                    // if the identifier is exposed, use the IdentId we already have for it
-                    // other modules depend on the symbol having that IdentId
-                    let symbol = Symbol::new(self.home, existing);
-
-                    self.locals.in_scope.set(existing.index(), true);
-                    self.locals.regions[existing.index()] = region;
-
-                    Ok((symbol, None))
-                } else {
-                    let ident_id = self.locals.introduce_into_scope_duplicate(existing, region);
-
-                    Ok((Symbol::new(self.home, ident_id), None))
-                }
-            }
         }
     }
 

compiler/collections/src/small_string_interner.rs

@@ -1,3 +1,5 @@
+use std::{fmt::Debug, mem::ManuallyDrop};
+
 /// Collection of small (length < u16::MAX) strings, stored compactly.
 #[derive(Clone, Default, PartialEq, Eq)]
 pub struct SmallStringInterner {
@@ -5,10 +7,54 @@ pub struct SmallStringInterner {
 
     // lengths could be Vec<u8>, but the mono refcount generation
     // stringifies Layout's and that creates > 256 character strings
-    lengths: Vec<u16>,
+    lengths: Vec<Length>,
     offsets: Vec<u32>,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq)]
+#[repr(transparent)]
+struct Length(i16);
+
+impl std::fmt::Debug for Length {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.kind().fmt(f)
+    }
+}
+
+impl Length {
+    #[inline(always)]
+    const fn kind(self) -> Kind {
+        if self.0 == 0 {
+            Kind::Emtpy
+        } else if self.0 > 0 {
+            Kind::Interned(self.0 as usize)
+        } else {
+            Kind::Generated(self.0.abs() as usize)
+        }
+    }
+
+    #[inline(always)]
+    const fn from_usize(len: usize) -> Self {
+        Self(len as i16)
+    }
+}
+
+enum Kind {
+    Generated(usize),
+    Emtpy,
+    Interned(usize),
+}
+
+impl Debug for Kind {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Generated(arg0) => write!(f, "Generated({})", arg0),
+            Self::Emtpy => write!(f, "Emtpy"),
+            Self::Interned(arg0) => write!(f, "Interned({})", arg0),
+        }
+    }
+}
+
 impl std::fmt::Debug for SmallStringInterner {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let strings: Vec<_> = self.iter().collect();
@@ -33,7 +79,19 @@ impl SmallStringInterner {
         }
     }
 
-    pub const fn from_parts(buffer: Vec<u8>, lengths: Vec<u16>, offsets: Vec<u32>) -> Self {
+    /// # Safety
+    ///
+    /// lengths must be non-negative integers less than 2^15
+    pub unsafe fn from_parts(buffer: Vec<u8>, lengths: Vec<u16>, offsets: Vec<u32>) -> Self {
+        // the recommended way of transmuting a vector
+        let mut lengths = ManuallyDrop::new(lengths);
+
+        let lengths = Vec::from_raw_parts(
+            lengths.as_mut_ptr().cast(),
+            lengths.len(),
+            lengths.capacity(),
+        );
+
         Self {
             buffer,
             lengths,
@@ -49,10 +107,10 @@ impl SmallStringInterner {
     pub fn insert(&mut self, string: &str) -> usize {
         let bytes = string.as_bytes();
 
-        assert!(bytes.len() < u16::MAX as usize);
+        assert!(bytes.len() < (1 << 15));
 
         let offset = self.buffer.len() as u32;
-        let length = bytes.len() as u16;
+        let length = Length::from_usize(bytes.len());
 
         let index = self.lengths.len();
 
@@ -90,9 +148,11 @@ impl SmallStringInterner {
 
         let offset = self.buffer.len();
         write!(self.buffer, "{}", index).unwrap();
-        let length = self.buffer.len() - offset;
 
-        self.lengths.push(length as u16);
+        // this is a generated name, so store it as a negative length
+        let length = Length(-((self.buffer.len() - offset) as i16));
+
+        self.lengths.push(length);
         self.offsets.push(offset as u32);
 
         index
@@ -105,17 +165,26 @@ impl SmallStringInterner {
 
     #[inline(always)]
     pub fn find_indices<'a>(&'a self, string: &'a str) -> impl Iterator<Item = usize> + 'a {
-        let target_length = string.len() as u16;
+        let target_length = string.len();
 
         // there can be gaps in the parts of the string that we use (because of updates)
         // hence we can't just sum the lengths we've seen so far to get the next offset
         self.lengths
             .iter()
             .enumerate()
-            .filter_map(move |(index, length)| {
+            .filter_map(move |(index, length)| match length.kind() {
-                if *length == target_length {
+                Kind::Generated(_) => None,
+                Kind::Emtpy => {
+                    if target_length == 0 {
+                        Some(index)
+                    } else {
+                        None
+                    }
+                }
+                Kind::Interned(length) => {
+                    if target_length == length {
                         let offset = self.offsets[index];
-                    let slice = &self.buffer[offset as usize..][..*length as usize];
+                        let slice = &self.buffer[offset as usize..][..length];
 
                         if string.as_bytes() == slice {
                             return Some(index);
@@ -123,17 +192,22 @@ impl SmallStringInterner {
                     }
 
                     None
+                }
             })
     }
 
     fn get(&self, index: usize) -> &str {
-        let length = self.lengths[index] as usize;
+        match self.lengths[index].kind() {
+            Kind::Emtpy => "",
+            Kind::Generated(length) | Kind::Interned(length) => {
                 let offset = self.offsets[index] as usize;
 
                 let bytes = &self.buffer[offset..][..length];
 
                 unsafe { std::str::from_utf8_unchecked(bytes) }
             }
+        }
+    }
 
     pub fn try_get(&self, index: usize) -> Option<&str> {
         if index < self.lengths.len() {
@@ -151,7 +225,7 @@ impl SmallStringInterner {
         // `buffer`, we can update them in-place
         self.buffer.extend(new_string.bytes());
 
-        self.lengths[index] = length as u16;
+        self.lengths[index] = Length::from_usize(length);
         self.offsets[index] = offset as u32;
     }
 

compiler/module/src/symbol.rs

@@ -531,7 +531,7 @@ impl IdentId {
 /// Stores a mapping between Ident and IdentId.
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct IdentIds {
-    interner: SmallStringInterner,
+    pub interner: SmallStringInterner,
 }
 
 impl IdentIds {
@@ -759,11 +759,13 @@ macro_rules! define_builtins {
                             }
                         };
 
-                        let interner = SmallStringInterner::from_parts (
+                        // Safety: all lengths are non-negative and smaller than 2^15
+                        let interner = unsafe {
+                            SmallStringInterner::from_parts (
                             BUFFER.as_bytes().to_vec(),
                             LENGTHS.to_vec(),
                             OFFSETS.to_vec(),
-                        );
+                        )};
 
                         IdentIds{ interner }
                     };

examples/hello-world/helloWorld.roc

@@ -8,4 +8,15 @@ app "helloWorld"
     imports []
     provides [ main ] to pf
 
-main = "Hello, World!\n"
+a = 
+    foobar = "Hello"
+
+    foobar
+
+b = 
+    foobar = "World"
+
+    foobar
+
+# main = "Hello, World!\n"
+main = Str.concat a b