Add Lint/TrailingRescueException (#512)

* Add Lint/TrailingRescueException

This prevents the use of Paths as the default value for a trailing exception,
and recommends the user use the block rescue instead to be able to filter by exception type

* Update src/ameba/rule/lint/trailing_rescue_exception.cr

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

* Update spec/ameba/rule/lint/trailing_rescue_exception_spec.cr

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

* Update src/ameba/rule/lint/trailing_rescue_exception.cr

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

* Update src/ameba/rule/lint/trailing_rescue_exception.cr

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

* Update src/ameba/rule/lint/trailing_rescue_exception.cr

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

* Update docs for `Lint/TrailingRescueException`

---------

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

spec/ameba/rule/lint/trailing_rescue_exception_spec.cr

@@ -0,0 +1,25 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Lint
+  subject = TrailingRescueException.new
+
+  it "passes for trailing rescue with literal values" do
+    expect_no_issues subject, <<-CRYSTAL
+        puts "hello" rescue "world"
+        puts :meow rescue 1234
+        CRYSTAL
+  end
+
+  it "passes for trailing rescue with class initialization" do
+    expect_no_issues subject, <<-CRYSTAL
+        puts "hello" rescue MyClass.new
+        CRYSTAL
+  end
+
+  it "fails if trailing rescue has exception name" do
+    expect_issue subject, <<-CRYSTAL
+        puts "hello" rescue MyException
+                          # ^^^^^^^^^^^ error: Trailing rescues with a path aren't allowed, use a block rescue instead to filter by exception type
+        CRYSTAL
+  end
+end

src/ameba/rule/lint/trailing_rescue_exception.cr

@@ -0,0 +1,53 @@
+module Ameba::Rule::Lint
+  # A rule that prohibits the common misconception about how trailing rescue statements work,
+  # preventing Paths (exception class names or otherwise) from being
+  # used as the trailing value. The value after the trailing rescue statement is the
+  # value to use if an exception occurs, not the exception for the rescue to capture.
+  #
+  # For example, this is considered invalid - if an exception occurs in `method.call`,
+  # `value` will be assigned the value of `MyException`:
+  #
+  # ```
+  # value = method.call("param") rescue MyException
+  # ```
+  #
+  # And should instead be written as this in order to capture only `MyException` exceptions:
+  #
+  # ```
+  # value = begin
+  #   method.call("param")
+  # rescue MyException
+  #   "default value"
+  # end
+  # ```
+  #
+  # Or to rescue all exceptions (instead of just `MyException`):
+  #
+  # ```
+  # value = method.call("param") rescue "default value"
+  # ```
+  #
+  # YAML configuration example:
+  #
+  # ```
+  # Lint/TrailingRescueException:
+  #   Enabled: true
+  # ```
+  class TrailingRescueException < Base
+    properties do
+      since_version "1.7.0"
+      description "Disallows trailing rescue with a path"
+    end
+
+    MSG = "Trailing rescues with a path aren't allowed, use a block rescue instead to filter by exception type"
+
+    def test(source, node : Crystal::ExceptionHandler)
+      return unless node.suffix &&
+                    (rescues = node.rescues) &&
+                    (resc = rescues.first?) &&
+                    resc.body.is_a?(Crystal::Path)
+
+      issue_for resc.body, MSG, prefer_name_location: true
+    end
+  end
+end