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A static code analysis tool with a focus on code consistency and teaching.
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Files
lib/credo/check/refactor/match_in_condition.ex
defmodule Credo.Check.Refactor.MatchInCondition do
use Credo.Check,
id: "EX4016",
param_defaults: [
allow_tagged_tuples: false
],
explanations: [
check: """
Pattern matching should only ever be used for simple assignments
inside `if` and `unless` clauses.
While this fine:
# okay, simple wildcard assignment:
if contents = File.read!("foo.txt") do
do_something(contents)
end
the following should be avoided, since it mixes a pattern match with a
condition and do/else blocks.
# considered too "complex":
if {:ok, contents} = File.read("foo.txt") do
do_something(contents)
end
# also considered "complex":
if allowed? && ( contents = File.read!("foo.txt") ) do
do_something(contents)
end
If you want to match for something and execute another block otherwise,
consider using a `case` statement:
case File.read("foo.txt") do
{:ok, contents} ->
do_something()
_ ->
do_something_else()
end
""",
params: [
allow_tagged_tuples:
"Allow tagged tuples in conditions, e.g. `if {:ok, contents} = File.read( \"foo.txt\") do`"
]
]
@condition_ops [:if, :unless]
@trigger "="
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
issue_meta = IssueMeta.for(source_file, params)
allow_tagged_tuples = Params.get(params, :allow_tagged_tuples, __MODULE__)
Credo.Code.prewalk(source_file, &traverse(&1, &2, allow_tagged_tuples, issue_meta))
end
# Skip if arguments is not enumerable
defp traverse({_op, _meta, nil} = ast, issues, _allow_tagged_tuples, _source_file) do
{ast, issues}
end
# TODO: consider for experimental check front-loader (ast)
# NOTE: we have to exclude the cases matching the above
for op <- @condition_ops do
defp traverse({unquote(op), _meta, arguments} = ast, issues, allow_tagged_tuples, issue_meta) do
# remove do/else blocks
condition_arguments = Enum.reject(arguments, &Keyword.keyword?/1)
new_issues =
Credo.Code.prewalk(
condition_arguments,
&traverse_condition(
&1,
&2,
unquote(op),
condition_arguments,
allow_tagged_tuples,
issue_meta
)
)
{ast, issues ++ new_issues}
end
end
defp traverse(ast, issues, _allow_tagged_tuples, _source_file) do
{ast, issues}
end
defp traverse_condition(
{:=, meta, arguments} = ast,
issues,
op,
op_arguments,
allow_tagged_tuples?,
issue_meta
) do
assignment_in_body? = Enum.member?(op_arguments, ast)
case arguments do
[{atom, _, nil}, _right] when is_atom(atom) ->
if assignment_in_body? do
{ast, issues}
else
new_issue = issue_for(op, meta[:line], issue_meta)
{ast, issues ++ [new_issue]}
end
[{tag_atom, {atom, _, nil}}, _right] when is_atom(atom) and is_atom(tag_atom) ->
if allow_tagged_tuples? do
{ast, issues}
else
new_issue = issue_for(op, meta[:line], issue_meta)
{ast, issues ++ [new_issue]}
end
_ ->
new_issue = issue_for(op, meta[:line], issue_meta)
{ast, issues ++ [new_issue]}
end
end
defp traverse_condition(ast, issues, _op, _op_arguments, _allow_tagged_tuples, _issue_meta) do
{ast, issues}
end
defp issue_for(op, line_no, issue_meta) do
format_issue(
issue_meta,
message: "There should be no matches in `#{op}` conditions.",
trigger: @trigger,
line_no: line_no
)
end
end