Erlang Error Index Content

Summary:
* W0011
* W0012
* W0013

Differential Revision: D49188397

fbshipit-source-id: 199cfbeb159bf327533f5cf7c6fa17029229f02b

website/docs/erlang-error-index/w/W0011.md

@@ -3,3 +3,23 @@ sidebar_position: 11
 ---
 
 # W0011 - Application Get Env
+
+## Error
+
+```erlang title="/app_a/src/main.erl"
+-module(main).
+
+get_app_b_env() ->
+    application:get_env(app_b, key).
+%%  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ warning: module `main` belongs to app `app_a`, but reads env for `app_b`
+```
+
+## Explanation
+
+The error message is indicating that a module belonging to an application `app_a` is attempting at reading the environment for a different application `app_b`.
+
+Erlang provides an [API](https://www.erlang.org/doc/man/application#get_env-2) to access the application environment of a different application from the one the calling module (or, to be more precise, the calling process executing that module) belongs to.
+
+This pattern can lead to subtle bugs since the target application (`app_b` in the above example) could not yet be loaded at the time of the call or it could be missing from a specific [release](https://www.erlang.org/doc/design_principles/release_structure.html).
+
+Sometimes accessing an other applicatioon environment is a totally acceptable behaviour. In those cases, the warning can be silenced via the [standard `elp:ignore` mechanirm](../erlang-error-index.md#ignoring-diagnostics).

website/docs/erlang-error-index/w/W0012.md

@@ -2,4 +2,36 @@
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-# W0012 - Missing Compile Warn Missing Spec
+# W0012 - Missing `warn_missing_spec` compiler attribute
+
+## Error
+
+```erlang
+   -module(main).
+
+   -compile([export_all, nowarn_export_all]).
+%% ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: Please add "-compile(warn_missing_spec)." or
+%%                                          | "-compile(warn_missing_spec_all)." to the module.
+%%                                          | If exported functions are not all specced, they need to be specced.
+```
+
+## Explanation
+
+The error is indicating that the given module does not have a `warn_missing_spec` or `warn_missing_spec_all` compiler attribute but it should have one.
+
+This diagnostic can be particularly useful for large code bases where type information (via `-spec` attributes) are added incrementally and it's not possible to specify the option globally.
+
+To fix this warning you can add one of the following compiler attributes:
+
+```erlang
+-compile(warn_missing_spec). %% To enable warnings on exported functions only
+-compile(warn_missing_spec_all). %% To enable warnings on all functions
+```
+
+Notice that multiple compiler attributes can be listed using the same attribute. For example:
+
+```erlang
+-compile([export_all, nowarn_export_all, warn_missing_spec]).
+```
+
+For more information about compiler attributes and their meaning see [here](https://www.erlang.org/doc/man/compile).

website/docs/erlang-error-index/w/W0013.md

@@ -3,3 +3,16 @@ sidebar_position: 13
 ---
 
 # W0013 - Misspelled Attribute
+
+## Error
+
+```erlang
+  -dyalizer({nowarn_function, f/0}).
+%% ^^^^^^^^ error: misspelled attribute, saw 'dyalizer' but expected 'dialyzer'
+```
+
+## Explanation
+
+The message is indicating that the attribute name is suspiciously similar to a _known_ one and it could therefore contain a typo.
+
+To fix the error either correct the attribute spelling or ignore the warning via [the standard `elp:ignore` mechanism](../erlang-error-index.md#ignoring-diagnostics).