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File 3321-erl_parse-Provide-friendlier-head-mismatch-errors.patch of Package erlang
From d74e9c575075d49a749a30079b96be8d453dca55 Mon Sep 17 00:00:00 2001 From: Johannes Christ <jc@jchri.st> Date: Thu, 8 Jun 2023 00:34:39 +0200 Subject: [PATCH] erl_parse: Provide friendlier "head mismatch" errors Given the following module: %% mismatch.erl -module(mismatch). -compile([export_all, nowarn_export_all]). test_it(ok) -> ok; verify_it(true) -> ok; verify_it(false) -> {error, was_false}. verify_it(false, Reason) -> {error, Reason}. On master, running `erlc mismatch.erl` currently reports: mismatch.erl:6:1: head mismatch % 6| verify_it(true) -> ok; % | ^ The previous clause that the parser is comparing to may not be obvious: The current compiler warning points to `verify_it/1`, whose two clauses are terminated properly. When more code is inbetween these two functions (think documentation, specs, comments) the time needed to find the mismatched clause can be a lot higher. I also believe that this will make the error easier to understand for people new to Erlang. With this commit, the compiler will output the following: mismatch.erl:6:1: head mismatch: previous function test_it/1 is distinct from verify_it/1. Is the semicolon in test_it/1 unwanted? % 6| verify_it(true) -> ok; % | ^ For functions that are defined with the same name but distinct arities, a separate error message is used, since the possibility of missed or superfluous arguments also arises here. The following module illustrates it: %% mismatch2.erl -module(mismatch2). -compile([export_all, nowarn_export_all]). verify_it(false) -> {error, was_false}; verify_it(false, Reason) -> {error, Reason}. The following error message is provided in this case: mismatch2.erl:6:1: head mismatch: function verify_it with arities 1 and 2 is regarded as two distinct functions. Is the number of arguments incorrect or is the semicolon in verify_it/1 unwanted? % 6| verify_it(false, Reason) -> {error, Reason}. % | ^ For tools matching on the output of the compiler warnings, this is a breaking change. I have so far only found Erlang LS which matches on this [1]. Adding support for the extended information should be trivial. [1]: https://github.com/erlang-ls/erlang_ls/blob/e315f9801d60e1ccbbfd444f32a33d00b0f6795d/apps/els_lsp/src/els_compiler_diagnostics.erl#L614 --- lib/compiler/test/error_SUITE.erl | 20 +++++++++++--- .../head_mismatch_same_function_name.erl | 26 +++++++++++++++++++ lib/stdlib/src/erl_parse.yrl | 17 ++++++++++-- 3 files changed, 58 insertions(+), 5 deletions(-) create mode 100644 lib/compiler/test/error_SUITE_data/head_mismatch_same_function_name.erl diff --git a/lib/compiler/test/error_SUITE.erl b/lib/compiler/test/error_SUITE.erl index f82fde9e8b..3250ebb3d6 100644 --- a/lib/compiler/test/error_SUITE.erl +++ b/lib/compiler/test/error_SUITE.erl @@ -22,8 +22,8 @@ -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, init_per_group/2,end_per_group/2, - head_mismatch_line/1,warnings_as_errors/1, bif_clashes/1, - transforms/1,maps_warnings/1,bad_utf8/1,bad_decls/1]). + head_mismatch_line/1, head_mismatch_same_function_name/1, warnings_as_errors/1, + bif_clashes/1, transforms/1,maps_warnings/1,bad_utf8/1,bad_decls/1]). %% Used by transforms/1 test case. -export([parse_transform/2]). @@ -35,7 +35,8 @@ all() -> groups() -> [{p,test_lib:parallel(), - [head_mismatch_line,warnings_as_errors,bif_clashes, + [head_mismatch_line,head_mismatch_same_function_name, + warnings_as_errors,bif_clashes, transforms,maps_warnings,bad_utf8,bad_decls]}]. init_per_suite(Config) -> @@ -177,6 +178,19 @@ bif_clashes(Config) when is_list(Config) -> head_mismatch_line(Config) when is_list(Config) -> [E|_] = get_compilation_errors(Config, "head_mismatch_line"), {{26,1}, Mod, Reason} = E, + ("head mismatch: previous function foo/1 is distinct from bar/1. " + "Is the semicolon in foo/1 unwanted?") = lists:flatten(Reason), + Mod:format_error(Reason), + ok. + +%% Tests that a head mismatch with the same function name reports a different error from above. +%% https://github.com/erlang/otp/pull/7383#issuecomment-1586564294 +head_mismatch_same_function_name(Config) when is_list(Config) -> + [E|_] = get_compilation_errors(Config, "head_mismatch_same_function_name"), + {{25,1}, Mod, Reason} = E, + ("head mismatch: function foo with arities 1 and 2 is regarded as " + "two distinct functions. Is the number of arguments incorrect " + "or is the semicolon in foo/1 unwanted?") = lists:flatten(Reason), Mod:format_error(Reason), ok. diff --git a/lib/compiler/test/error_SUITE_data/head_mismatch_same_function_name.erl b/lib/compiler/test/error_SUITE_data/head_mismatch_same_function_name.erl new file mode 100644 index 0000000000..2e02ca42c9 --- /dev/null +++ b/lib/compiler/test/error_SUITE_data/head_mismatch_same_function_name.erl @@ -0,0 +1,26 @@ +%% +%% %CopyrightBegin% +%% +%% Copyright Ericsson AB 1998-2016. All Rights Reserved. +%% +%% Licensed under the Apache License, Version 2.0 (the "License"); +%% you may not use this file except in compliance with the License. +%% You may obtain a copy of the License at +%% +%% http://www.apache.org/licenses/LICENSE-2.0 +%% +%% Unless required by applicable law or agreed to in writing, software +%% distributed under the License is distributed on an "AS IS" BASIS, +%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +%% See the License for the specific language governing permissions and +%% limitations under the License. +%% +%% %CopyrightEnd% +-module(head_mismatch_same_function_name). + +-export([foo/1, foo/2]). + +foo({A, B}) -> + A + B; +foo(Other, State) -> + {Other, State}. diff --git a/lib/stdlib/src/erl_parse.yrl b/lib/stdlib/src/erl_parse.yrl index bef858cdc5..a1e41958a4 100644 --- a/lib/stdlib/src/erl_parse.yrl +++ b/lib/stdlib/src/erl_parse.yrl @@ -1499,8 +1499,21 @@ check_clauses(Cs, Name, Arity) -> [case C of {clause,A,N,As,G,B} when N =:= Name, length(As) =:= Arity -> {clause,A,As,G,B}; - {clause,A,_N,_As,_G,_B} -> - ret_err(A, "head mismatch") + {clause,A,N,As,_G,_B} when N =:= Name -> + Detail = io_lib:format( + "head mismatch: function ~s with arities ~w and ~w is " + "regarded as two distinct functions. Is the number of " + "arguments incorrect or is the semicolon in ~s/~w unwanted?", + [Name, Arity, length(As), Name, Arity] + ), + ret_err(A, Detail); + {clause,A,N,As,_G,_B} -> + Detail = io_lib:format( + "head mismatch: previous function ~s/~w is distinct from ~s/~w. " + "Is the semicolon in ~s/~w unwanted?", + [Name, Arity, N, length(As), Name, Arity] + ), + ret_err(A, Detail) end || C <- Cs]. build_try(A,Es,Scs,{Ccs,As}) -> -- 2.35.3
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