feat: add hover docs for use-chain injected functions with @callback fallback

internal/lsp/hover.go

@@ -31,6 +31,18 @@ func (s *Server) hoverFromFile(function string, result store.LookupResult) (*pro
 	} else {
 		doc, spec = extractDocAbove(lines, defIdx)
 		signature = extractSignature(lines, defIdx)
+
+		// Fallback: if the def has no doc (e.g. inline def injected by a
+		// __using__ macro), look for a @callback with the same name in the
+		// same file and extract its doc/spec instead.
+		if doc == "" && spec == "" {
+			if cbIdx := findCallbackLine(lines, function); cbIdx >= 0 {
+				doc, spec = extractDocAbove(lines, cbIdx)
+				if spec == "" {
+					spec = extractMultiLineAttr(lines, cbIdx)
+				}
+			}
+		}
 	}
 
 	content := formatHoverContent(doc, spec, signature)
@@ -214,6 +226,38 @@ func extractModuledoc(lines []string, moduleIdx int) string {
 	return ""
 }
 
+// findCallbackLine scans for a @callback or @macrocallback line that defines
+// the given function name and returns its 0-based line index, or -1.
+func findCallbackLine(lines []string, function string) int {
+	cbPrefix := "@callback " + function
+	mcbPrefix := "@macrocallback " + function
+	for i, line := range lines {
+		trimmed := strings.TrimSpace(line)
+		if strings.HasPrefix(trimmed, cbPrefix) && (len(trimmed) == len(cbPrefix) || trimmed[len(cbPrefix)] == '(' || trimmed[len(cbPrefix)] == ' ') {
+			return i
+		}
+		if strings.HasPrefix(trimmed, mcbPrefix) && (len(trimmed) == len(mcbPrefix) || trimmed[len(mcbPrefix)] == '(' || trimmed[len(mcbPrefix)] == ' ') {
+			return i
+		}
+	}
+	return -1
+}
+
+// extractMultiLineAttr collects a potentially multi-line module attribute
+// starting at idx (e.g. @callback, @spec). Continuation lines are collected
+// until an empty line, another attribute, or a definition is encountered.
+func extractMultiLineAttr(lines []string, idx int) string {
+	collected := []string{lines[idx]}
+	for i := idx + 1; i < len(lines); i++ {
+		trimmed := strings.TrimSpace(lines[i])
+		if trimmed == "" || strings.HasPrefix(trimmed, "@") || strings.HasPrefix(trimmed, "def") {
+			break
+		}
+		collected = append(collected, lines[i])
+	}
+	return strings.TrimSpace(strings.Join(collected, "\n"))
+}
+
 func extractQuotedString(s string) string {
 	if len(s) < 2 || s[0] != '"' {
 		return ""

internal/lsp/hover_test.go

@@ -1026,3 +1026,133 @@ end`
 		t.Errorf("expected submodule in hover, got %q", hover.Contents.Value)
 	}
 }
+
+func TestHover_QualifiedCallViaUseChain(t *testing.T) {
+	server, cleanup := setupTestServer(t)
+	defer cleanup()
+
+	// SharedLib.Storage defines __using__ that imports SharedLib.Queryable
+	storageSrc := `defmodule SharedLib.Storage do
+  defmacro __using__(_opts) do
+    quote do
+      import SharedLib.Queryable
+    end
+  end
+end`
+	queryableSrc := `defmodule SharedLib.Queryable do
+  @doc "Fetches all records matching the query."
+  def all(queryable), do: queryable
+end`
+
+	// MyApp.Repo uses SharedLib.Storage, so all/1 is injected
+	repoSrc := `defmodule MyApp.Repo do
+  use SharedLib.Storage
+end`
+
+	callerSrc := `defmodule MyApp.Accounts do
+  alias MyApp.Repo
+
+  def list do
+    Repo.all(User)
+  end
+end`
+
+	indexFile(t, server.store, server.projectRoot, "lib/storage.ex", storageSrc)
+	storageURI := "file://" + filepath.Join(server.projectRoot, "lib/storage.ex")
+	server.docs.Set(storageURI, storageSrc)
+
+	indexFile(t, server.store, server.projectRoot, "lib/queryable.ex", queryableSrc)
+
+	indexFile(t, server.store, server.projectRoot, "lib/repo.ex", repoSrc)
+	repoURI := "file://" + filepath.Join(server.projectRoot, "lib/repo.ex")
+	server.docs.Set(repoURI, repoSrc)
+
+	callerURI := "file://" + filepath.Join(server.projectRoot, "lib/accounts.ex")
+	server.docs.Set(callerURI, callerSrc)
+
+	// line 4 (0-indexed): `    Repo.all(User)` — col 9 is on `all`
+	hover := hoverAt(t, server, callerURI, 4, 9)
+	if hover == nil {
+		t.Fatal("expected hover result for Repo.all resolved via use-chain, got nil")
+	}
+	if !strings.Contains(hover.Contents.Value, "Fetches all records") {
+		t.Errorf("expected doc from use-chain source, got %q", hover.Contents.Value)
+	}
+}
+
+func TestHover_QualifiedCallViaUseChain_CallbackDoc(t *testing.T) {
+	server, cleanup := setupTestServer(t)
+	defer cleanup()
+
+	// SharedLib.Storage defines @callback with @doc and injects bare def via __using__.
+	// The @callback for get spans multiple lines to test multi-line extraction.
+	storageSrc := `defmodule SharedLib.Storage do
+  @doc """
+  Fetches all records from the data store.
+  """
+  @callback all(queryable :: term) :: [term]
+
+  @doc """
+  Fetches a single record by its ID.
+  """
+  @callback get(queryable :: term, id :: term) ::
+              term | nil
+
+  defmacro __using__(_opts) do
+    quote do
+      @behaviour SharedLib.Storage
+
+      def all(queryable), do: queryable
+      def get(queryable, id), do: nil
+    end
+  end
+end`
+
+	repoSrc := `defmodule MyApp.Repo do
+  use SharedLib.Storage
+end`
+
+	callerSrc := `defmodule MyApp.Accounts do
+  alias MyApp.Repo
+
+  def list do
+    Repo.all(User)
+  end
+
+  def find(id) do
+    Repo.get(User, id)
+  end
+end`
+
+	indexFile(t, server.store, server.projectRoot, "lib/storage.ex", storageSrc)
+	storageURI := "file://" + filepath.Join(server.projectRoot, "lib/storage.ex")
+	server.docs.Set(storageURI, storageSrc)
+
+	indexFile(t, server.store, server.projectRoot, "lib/repo.ex", repoSrc)
+	repoURI := "file://" + filepath.Join(server.projectRoot, "lib/repo.ex")
+	server.docs.Set(repoURI, repoSrc)
+
+	callerURI := "file://" + filepath.Join(server.projectRoot, "lib/accounts.ex")
+	server.docs.Set(callerURI, callerSrc)
+
+	// line 4 (0-indexed): `    Repo.all(User)` — col 9 is on `all`
+	hover := hoverAt(t, server, callerURI, 4, 9)
+	if hover == nil {
+		t.Fatal("expected hover result for Repo.all via callback doc, got nil")
+	}
+	if !strings.Contains(hover.Contents.Value, "Fetches all records") {
+		t.Errorf("expected callback doc for all, got %q", hover.Contents.Value)
+	}
+
+	// line 8 (0-indexed): `    Repo.get(User, id)` — col 9 is on `get`
+	hover = hoverAt(t, server, callerURI, 8, 9)
+	if hover == nil {
+		t.Fatal("expected hover result for Repo.get via callback doc, got nil")
+	}
+	if !strings.Contains(hover.Contents.Value, "Fetches a single record") {
+		t.Errorf("expected callback doc for get, got %q", hover.Contents.Value)
+	}
+	if !strings.Contains(hover.Contents.Value, "term | nil") {
+		t.Errorf("expected full multi-line callback spec for get, got %q", hover.Contents.Value)
+	}
+}

internal/lsp/server.go

@@ -2696,6 +2696,12 @@ func (s *Server) Hover(ctx context.Context, params *protocol.HoverParams) (*prot
 		if err == nil && len(results) > 0 {
 			return s.hoverFromFile(functionName, results[0])
 		}
+
+		// Not directly defined — the function may have been injected by a
+		// `use` macro in fullModule's source (e.g. Ecto.Repo injects `all`).
+		if results := s.lookupThroughUseOf(fullModule, functionName); len(results) > 0 {
+			return s.hoverFromFile(functionName, results[0])
+		}
 	}
 
 	results, err := s.store.LookupModule(fullModule)