Improve reporting for doc links problems

crates/compiler/load_internal/src/file.rs

@@ -3381,6 +3381,7 @@ fn finish(
 
     LoadedModule {
         module_id: state.root_id,
+        filename: state.root_path,
         interns,
         solved,
         can_problems: state.module_cache.can_problems,

crates/compiler/load_internal/src/module.rs

@@ -30,6 +30,7 @@ use std::time::{Duration, Instant};
 #[derive(Debug)]
 pub struct LoadedModule {
     pub module_id: ModuleId,
+    pub filename: PathBuf,
     pub interns: Interns,
     pub solved: Solved<Subs>,
     pub can_problems: MutMap<ModuleId, Vec<roc_problem::can::Problem>>,
@@ -54,6 +55,13 @@ pub struct LoadedModule {
 }
 
 impl LoadedModule {
+    /// Infer the filename for the given ModuleId, based on this root module's filename.
+    pub fn filename(&self, module_id: ModuleId) -> PathBuf {
+        let module_name = self.interns.module_name(module_id);
+
+        module_name.filename(&self.filename)
+    }
+
     pub fn total_problems(&self) -> usize {
         let mut total = 0;
 

crates/compiler/module/src/ident.rs

@@ -1,5 +1,8 @@
 pub use roc_ident::IdentStr;
-use std::fmt::{self, Debug};
+use std::{
+    fmt::{self, Debug},
+    path::{Path, PathBuf},
+};
 
 use crate::symbol::PQModuleName;
 
@@ -45,6 +48,19 @@ impl<'a> QualifiedModuleName<'a> {
 #[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub struct ModuleName(IdentStr);
 
+impl ModuleName {
+    /// Given the root module's path, infer this module's path based on its name.
+    pub fn filename(&self, root_filename: impl AsRef<Path>) -> PathBuf {
+        let mut answer = root_filename.as_ref().with_file_name("");
+
+        for part in self.split(".") {
+            answer = answer.join(part);
+        }
+
+        answer.with_extension("roc")
+    }
+}
+
 impl std::ops::Deref for ModuleName {
     type Target = str;