Add fix-it hint for missing return statement in assignment operators (PR c++/85523)

gcc/cp/ChangeLog:

	PR c++/85523
	* decl.c: Include "gcc-rich-location.h".
	(add_return_star_this_fixit): New function.
	(finish_function): When warning about missing return statements in
	functions returning non-void, add a "return *this;" fix-it hint for
	assignment operators.

gcc/testsuite/ChangeLog:

	PR c++/85523
	* g++.dg/pr85523.C: New test.


Co-Authored-By: Jonathan Wakely <jwakely@redhat.com>

From-SVN: r263298

gcc/cp/ChangeLog

@@ -1,3 +1,12 @@
+2018-08-03  David Malcolm  <dmalcolm@redhat.com>
+	    Jonathan Wakely  <jwakely@redhat.com>
+
+	* decl.c: Include "gcc-rich-location.h".
+	(add_return_star_this_fixit): New function.
+	(finish_function): When warning about missing return statements in
+	functions returning non-void, add a "return *this;" fix-it hint for
+	assignment operators.
+
 2018-08-03  Jason Merrill  <jason@redhat.com>
 
 	PR c++/86706

gcc/cp/decl.c

@@ -15710,6 +15710,22 @@ maybe_save_function_definition (tree fun)
     register_constexpr_fundef (fun, DECL_SAVED_TREE (fun));
 }
 
+/* Attempt to add a fix-it hint to RICHLOC suggesting the insertion
+   of "return *this;" immediately before its location, using FNDECL's
+   first statement (if any) to give the indentation, if appropriate.  */
+
+static void
+add_return_star_this_fixit (gcc_rich_location *richloc, tree fndecl)
+{
+  location_t indent = UNKNOWN_LOCATION;
+  tree stmts = expr_first (DECL_SAVED_TREE (fndecl));
+  if (stmts)
+    indent = EXPR_LOCATION (stmts);
+  richloc->add_fixit_insert_formatted ("return *this;",
+				       richloc->get_loc (),
+				       indent);
+}
+
 /* Finish up a function declaration and compile that function
    all the way to assembler language output.  The free the storage
    for the function definition. INLINE_P is TRUE if we just
@@ -15903,8 +15919,21 @@ finish_function (bool inline_p)
       && !DECL_DESTRUCTOR_P (fndecl)
       && targetm.warn_func_return (fndecl))
     {
-      warning (OPT_Wreturn_type,
- 	       "no return statement in function returning non-void");
+      gcc_rich_location richloc (input_location);
+      /* Potentially add a "return *this;" fix-it hint for
+	 assignment operators.  */
+      if (IDENTIFIER_ASSIGN_OP_P (DECL_NAME (fndecl)))
+	{
+	  tree valtype = TREE_TYPE (DECL_RESULT (fndecl));
+	  if (TREE_CODE (valtype) == REFERENCE_TYPE
+	      && same_type_ignoring_top_level_qualifiers_p
+		  (TREE_TYPE (valtype), TREE_TYPE (current_class_ref)))
+	    if (global_dc->option_enabled (OPT_Wreturn_type,
+					   global_dc->option_state))
+	      add_return_star_this_fixit (&richloc, fndecl);
+	}
+      warning_at (&richloc, OPT_Wreturn_type,
+		  "no return statement in function returning non-void");
       TREE_NO_WARNING (fndecl) = 1;
     }
 

gcc/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2018-08-03  David Malcolm  <dmalcolm@redhat.com>
+	    Jonathan Wakely  <jwakely@redhat.com>
+
+	PR c++/85523
+	* g++.dg/pr85523.C: New test.
+
 2018-08-03  Bogdan Harjoc  <harjoc@gmail.com>
 
 	PR c/86690

gcc/testsuite/g++.dg/pr85523.C

@@ -0,0 +1,88 @@
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+/* Verify that we emit a "return *this;" fix-it hint for
+   a missing return in an assignment operator.  */
+
+struct s1 {
+  s1& operator=(const s1&) { } // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
+   s1& operator=(const s1&) { }
+                              ^
+                              return *this;
+     { dg-end-multiline-output "" } */
+};
+
+/* Likewise for +=.  */
+
+struct s2 {
+  s2& operator+=(const s2&) {} // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
+   s2& operator+=(const s2&) {}
+                              ^
+                              return *this;
+     { dg-end-multiline-output "" } */
+};
+
+/* No warning for "void" return.  */
+
+struct s3 {
+  void operator=(const s3&) { }
+};
+
+/* We shouldn't issue the fix-it hint if the return type isn't right.  */
+
+struct s4 {
+  int operator=(int) { } // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
+   int operator=(int) { }
+                        ^
+     { dg-end-multiline-output "" } */
+};
+
+/* Example of a multi-line fix-it hint.  */
+
+struct s5 {
+  int i;
+  s5& operator=(const s5& z) {
+    i = z.i;
+  } // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
++    return *this;
+   }
+   ^
+     { dg-end-multiline-output "" } */
+};
+
+/* Example of a multi-line fix-it hint with other statements.  */
+
+extern void log (const char *);
+struct s6 {
+  int i;
+  s6& operator=(const s6& z) {
+    log ("operator=\n");
+    i = z.i;
+  } // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
++    return *this;
+   }
+   ^
+     { dg-end-multiline-output "" } */
+};
+
+/* Another example of a multi-line fix-it hint with other statements.  */
+
+struct s7 {
+  int i;
+  s7& operator=(const s6& z) {
+    if (z.i)
+      log ("operator=\n");
+    else
+      log ("operator=\n");
+    i = z.i;
+  } // { dg-warning "no return statement in function returning non-void" }
+  /* { dg-begin-multiline-output "" }
++    return *this;
+   }
+   ^
+     { dg-end-multiline-output "" } */
+};