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erl_lint: Warn on updating map/record literals #8069

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Feb 1, 2024
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erl_lint: Warn on updating map/record literals #8069

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43 changes: 40 additions & 3 deletions lib/stdlib/src/erl_lint.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -316,6 +316,8 @@ format_error({obsolete_guard_overridden,Test}) ->
format_error({too_many_arguments,Arity}) ->
io_lib:format("too many arguments (~w) - "
"maximum allowed is ~w", [Arity,?MAX_ARGUMENTS]);
format_error(update_literal) ->
"expression updates a literal";
%% --- patterns and guards ---
format_error(illegal_pattern) -> "illegal pattern";
format_error(illegal_map_key) -> "illegal map key in pattern";
Expand Down Expand Up @@ -682,6 +684,9 @@ start(File, Opts) ->
true, Opts)},
{match_float_zero,
bool_option(warn_match_float_zero, nowarn_match_float_zero,
true, Opts)},
{update_literal,
bool_option(warn_update_literal, nowarn_update_literal,
true, Opts)}
],
Enabled1 = [Category || {Category,true} <- Enabled0],
Expand Down Expand Up @@ -2429,10 +2434,10 @@ expr({tuple,_Anno,Es}, Vt, St) ->
expr_list(Es, Vt, St);
expr({map,_Anno,Es}, Vt, St) ->
map_fields(Es, Vt, check_assoc_fields(Es, St), fun expr_list/3);
expr({map,_Anno,Src,Es}, Vt, St) ->
expr({map,Anno,Src,Es}, Vt, St) ->
{Svt,St1} = expr(Src, Vt, St),
{Fvt,St2} = map_fields(Es, Vt, St1, fun expr_list/3),
{vtupdate(Svt, Fvt),St2};
{vtupdate(Svt, Fvt), warn_if_literal_update(Anno, Src, St2)};
expr({record_index,Anno,Name,Field}, _Vt, St) ->
check_record(Anno, Name, St,
fun (Dfs, St1) -> record_field(Field, Name, Dfs, St1) end);
Expand All @@ -2455,7 +2460,7 @@ expr({record,Anno,Rec,Name,Upds}, Vt, St0) ->
update_fields(Upds, Name, Dfs, Vt, St)
end ),
case has_wildcard_field(Upds) of
no -> {vtmerge(Rvt, Usvt),St2};
no -> {vtmerge(Rvt, Usvt), warn_if_literal_update(Anno, Rec, St2)};
WildAnno -> {[],add_error(WildAnno, {wildcard_in_update,Name}, St2)}
end;
expr({bin,_Anno,Fs}, Vt, St) ->
Expand Down Expand Up @@ -4151,6 +4156,38 @@ has_wildcard_field([{record_field,_Af,{var,Aa,'_'},_Val}|_Fs]) -> Aa;
has_wildcard_field([_|Fs]) -> has_wildcard_field(Fs);
has_wildcard_field([]) -> no.

%% Raises a warning when updating a (map, record) literal, as that is most
%% likely unintentional. For example, if we forget a comma in a list like the
%% following:
%%
%% -record(foo, {bar}).
%%
%% list() ->
%% [
%% #foo{bar = foo} %% MISSING COMMA!
%% #foo{bar = bar}
%% ].
%%
%% We only raise a warning when the expression-to-be-updated is a map or a
%% record, as better warnings will be raised elsewhere for other funny
%% constructs.
warn_if_literal_update(Anno, Expr, St) ->
case is_literal_update(Expr) andalso is_warn_enabled(update_literal, St) of
true -> add_warning(Anno, update_literal, St);
false -> St
end.

is_literal_update({record, _, Inner, _, _}) ->
is_literal_update(Inner);
is_literal_update({record, _, _, _}) ->
true;
is_literal_update({map, _, Inner, _}) ->
is_literal_update(Inner);
is_literal_update({map, _, _}) ->
true;
is_literal_update(_Expr) ->
false.

%% check_remote_function(Anno, ModuleName, FuncName, [Arg], State) -> State.
%% Perform checks on known remote calls.

Expand Down
40 changes: 34 additions & 6 deletions lib/stdlib/test/erl_lint_SUITE.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,8 @@
redefined_builtin_type/1,
tilde_k/1,
match_float_zero/1,
undefined_module/1]).
undefined_module/1,
update_literal/1]).

suite() ->
[{ct_hooks,[ts_install_cth]},
Expand Down Expand Up @@ -119,7 +120,8 @@ all() ->
singleton_type_var_errors,
documentation_attributes,
match_float_zero,
undefined_module].
undefined_module,
update_literal].

groups() ->
[{unused_vars_warn, [],
Expand Down Expand Up @@ -4049,10 +4051,11 @@ maps(Config) ->
ok.
">>,
[],
{errors,[{{2,24},erl_lint,illegal_map_construction},
{{4,24},erl_lint,illegal_map_construction},
{{8,36},erl_lint,illegal_map_construction}],
[]}},
{error,
[{{2,24},erl_lint,illegal_map_construction},
{{4,24},erl_lint,illegal_map_construction},
{{8,36},erl_lint,illegal_map_construction}],
[{{5,20},erl_lint,update_literal}]}},
{illegal_pattern,
<<"t(#{ a := A,
c => d,
Expand Down Expand Up @@ -5330,6 +5333,31 @@ undefined_module(Config) ->

ok.

update_literal(Config) ->
Ts = [{update_record_literal,
<<"-record(a, {b}).
t() -> #a{}#a{}#a{b=aoeu}.
k() -> A = #a{}, A#a{}#a{b=aoeu}.">>,
[],
{warnings,[{{2,25},erl_lint,update_literal},
{{2,29},erl_lint,update_literal}]}},
{update_map_literal_assoc,
<<"t() -> #{}#{}#{b=>aoeu}.
k() -> A = #{}, A#{}#{b=>aoeu}.">>,
[],
{warnings,[{{1,31},erl_lint,update_literal},
{{1,34},erl_lint,update_literal}]}},
{update_map_literal_exact,
<<"t() -> #{}#{}#{b:=aoeu}.
k() -> A = #{}, A#{}#{b:=aoeu}.">>,
[],
{warnings,[{{1,31},erl_lint,update_literal},
{{1,34},erl_lint,update_literal}]}}
],
[] = run(Config, Ts),

ok.

%%%
%%% Common utilities.
%%%
Expand Down
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