started using scope properly, improved error backtrace conversion

compiler/module/src/module_err.rs

@@ -1,5 +1,7 @@
 use snafu::{Backtrace, Snafu};
 
+use crate::symbol::IdentId;
+
 #[derive(Debug, Snafu)]
 #[snafu(visibility(pub))]
 pub enum ModuleError {
@@ -13,6 +15,16 @@ pub enum ModuleError {
         all_ident_ids: String,
         backtrace: Backtrace,
     },
+    #[snafu(display(
+        "IdentIdNotFound: I could not find IdentId {:?} in ident_ids {:?}.",
+        ident_id,
+        ident_ids_str
+    ))]
+    IdentIdNotFound {
+        ident_id: IdentId,
+        ident_ids_str: String,
+        backtrace: Backtrace,
+    },
 }
 
 pub type ModuleResult<T, E = ModuleError> = std::result::Result<T, E>;

compiler/module/src/symbol.rs

@@ -1,5 +1,5 @@
 use crate::ident::{Ident, ModuleName};
-use crate::module_err::{ModuleIdNotFound, ModuleResult};
+use crate::module_err::{ModuleIdNotFound, IdentIdNotFound, ModuleResult};
 use roc_collections::all::{default_hasher, MutMap, SendMap};
 use roc_ident::IdentStr;
 use roc_region::all::Region;
@@ -264,6 +264,15 @@ impl Interns {
                 all_ident_ids: format!("{:?}", self.all_ident_ids),
             })
     }
+
+    pub fn get_module_ident_ids_mut(&mut self, module_id: &ModuleId) -> ModuleResult<&mut IdentIds> {
+        self.all_ident_ids
+            .get_mut(module_id)
+            .with_context(|| ModuleIdNotFound {
+                module_id: format!("{:?}", module_id),
+                all_ident_ids: "I could not return all_ident_ids here because of borrowing issues.",
+            })
+    }
 }
 
 #[cfg(debug_assertions)]
@@ -634,6 +643,18 @@ impl IdentIds {
     pub fn get_name(&self, id: IdentId) -> Option<&Ident> {
         self.by_id.get(id.0 as usize)
     }
+
+    pub fn get_name_str_res(&self, ident_id: IdentId) -> ModuleResult<&str> {
+        Ok(self
+            .get_name(ident_id)
+            .with_context(|| IdentIdNotFound {
+                ident_id,
+                ident_ids_str: format!("{:?}", self),
+            })?
+            .as_inline_str()
+            .as_str()
+        )
+    }
 }
 
 // BUILTINS