From 5e4e67c1a4cce3f813f7d4d27df8c2028c92c77f Mon Sep 17 00:00:00 2001
From: "Paulo F. Oliveira" <paulo.ferraz.oliveira@gmail.com>
Date: Tue, 8 Dec 2020 17:37:07 +0000
Subject: [PATCH] Document previously hidden (though very useful) compiler
 options

---
 lib/compiler/doc/src/compile.xml   | 14 ++++++++++++++
 lib/stdlib/test/erl_lint_SUITE.erl | 25 +++++++++++++++++++++++--
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/lib/compiler/doc/src/compile.xml b/lib/compiler/doc/src/compile.xml
index 94180b47332b..0e2f29aa9d0b 100644
--- a/lib/compiler/doc/src/compile.xml
+++ b/lib/compiler/doc/src/compile.xml
@@ -696,6 +696,20 @@ module.beam: module.erl \
                 fallbacks by accident. Use this option to turn off this kind of
                 warnings.</p>
           </item>
+
+          <tag><c>warn_missing_spec</c></tag>
+          <item>
+              <p>By default, warnings are not emitted when a specification
+                (or contract) for an exported function is not given. Use this
+                option to turn on this kind of warning.</p>
+          </item>
+
+          <tag><c>warn_missing_spec_all</c></tag>
+          <item>
+              <p>By default, warnings are not emitted when a specification
+                (or contract) for an exported or unexported function is not
+                given. Use this option to turn on this kind of warning.</p>
+          </item>
         </taglist>
 
 	<p>Another class of warnings is generated by the compiler
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index 20f8407f851a..85567c88cb34 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -70,7 +70,8 @@
          otp_14285/1, otp_14378/1,
          external_funs/1,otp_15456/1,otp_15563/1,
          unused_type/1,removed/1, otp_16516/1,
-         inline_nifs/1]).
+         inline_nifs/1,
+         warn_missing_spec/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -93,7 +94,7 @@ all() ->
      record_errors, otp_11879_cont, non_latin1_module, otp_14323,
      stacktrace_syntax, otp_14285, otp_14378, external_funs,
      otp_15456, otp_15563, unused_type, removed, otp_16516,
-     inline_nifs].
+     inline_nifs, warn_missing_spec].
 
 groups() -> 
     [{unused_vars_warn, [],
@@ -4448,6 +4449,26 @@ inline_nifs(Config) ->
            {warnings,[{2,erl_lint,nif_inline}]}}],
     [] = run(Config, Ts).
 
+warn_missing_spec(Config) ->
+    Test = <<"-export([external_with_spec/0, external_no_spec/0]).
+
+              -spec external_with_spec() -> ok.
+              external_with_spec() -> ok.
+
+              external_no_spec() -> ok.
+
+              -spec internal_with_spec() -> ok.
+              internal_with_spec() -> ok.
+
+              internal_no_spec() -> ok.">>,
+    run(Config, [
+        {warn_missing_spec, Test, [warn_missing_spec],
+            {warnings, [{6, erl_lint, {missing_spec, {external_no_spec, 0}}}]}},
+        {warn_missing_spec_all, Test, [warn_missing_spec_all],
+            {warnings, [{6, erl_lint, {missing_spec, {external_no_spec, 0}}},
+                        {11, erl_lint, {missing_spec, {internal_no_spec, 0}}}]}}
+    ]).
+
 format_error(E) ->
     lists:flatten(erl_lint:format_error(E)).