Add MultilineScript linter

Change-Id: I257b82c0bc5cdaed215579def77074cea8084deb
Reviewed-on: http://gerrit.causes.com/47624
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

CHANGELOG.md

@@ -9,6 +9,8 @@
   with 1.8-style hash rockets spanning multiple lines
 * Fix `RuboCop` linter to not report `Style/EmptyElse` warnings for HAML code
   containing `if`/`else` blocks containing only HAML filters
+* Add `MultilineScript` linter to report scripts with trailing operators that
+  should be merged with the following line
 
 ## 0.11.0
 

config/default.yml

@@ -40,6 +40,9 @@ linters:
   MultilinePipe:
     enabled: true
 
+  MultilineScript:
+    enabled: true
+
   ObjectReferenceAttributes:
     enabled: true
 

lib/haml_lint/linter/README.md

@@ -12,6 +12,7 @@ Below is a list of linters supported by `haml-lint`, ordered alphabetically.
 * [LeadingCommentSpace](#leadingcommentspace)
 * [LineLength](#linelength)
 * [MultilinePipe](#multilinepipe)
+* [MultilineScript](#multilinescript)
 * [ObjectReferenceAttributes](#objectreferenceattributes)
 * [RuboCop](#rubocop)
 * [RubyComments](#rubycomments)
@@ -242,6 +243,45 @@ The multiline bar was
 almost always suggests an unnecessarily complicated template that should have
 its logic extracted into a helper.
 
+## MultilineScript
+
+Don't span Ruby script over multiple lines using operators.
+
+**Bad**
+```haml
+- if condition ||
+-    other_condition
+  Display something!
+```
+
+**Good**
+```haml
+- if condition || other_condition
+  Display something!
+```
+
+While writing code this way may sometimes work, it is actually a result of a
+quirk in how HAML generates code from a template. While the following code
+will compile and run:
+
+```haml
+- if condition ||
+-    other_condition
+  Display something!
+```
+
+...this code will fail with a parse error:
+
+```haml
+- if condition ||
+-    other_condition
+  Display something!
+- else
+  Otherwise display this!
+```
+
+Thus it's best to stay away from writing code this way.
+
 ## ObjectReferenceAttributes
 
 Don't use the

lib/haml_lint/linter/multiline_script.rb

@@ -0,0 +1,43 @@
+module HamlLint
+  # Checks scripts spread over multiple lines.
+  class Linter::MultilineScript < Linter
+    include LinterRegistry
+
+    # List of operators that can split a script into two lines that we want to
+    # alert on.
+    SPLIT_OPERATORS = %w[
+      || or && and
+      ||= &&=
+      ^ << >> | &
+      <<= >>= |= &=
+      + - * / ** %
+      += -= *= /= **= %=
+      < <= <=> >= >
+      = == === != =~ !~
+      .. ...
+      ? :
+      not
+      if unless while until
+      begin
+    ].to_set
+
+    def visit_script(node)
+      check(node)
+    end
+
+    def visit_silent_script(node)
+      check(node)
+    end
+
+    private
+
+    def check(node)
+      operator = node.script[/\s+(\S+)\z/, 1]
+      if SPLIT_OPERATORS.include?(operator)
+        add_lint(node,
+                 "Script with trailing operator `#{operator}` should be " \
+                 'merged with the script on the following line')
+      end
+    end
+  end
+end

spec/haml_lint/linter/multiline_script_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe HamlLint::Linter::MultilineScript do
+  include_context 'linter'
+
+  context 'when silent script is split with a Boolean operator' do
+    let(:haml) { <<-HAML }
+      - if condition ||
+      - true
+        Result
+    HAML
+
+    it { should report_lint line: 1 }
+  end
+
+  context 'when silent script is split with an equality operator' do
+    let(:haml) { <<-HAML }
+      - if condition ==
+      - something
+        Result
+    HAML
+
+    it { should report_lint line: 1 }
+  end
+
+  context 'when script is split with a binary operator' do
+    let(:haml) { <<-HAML }
+      = 1 +
+      = 2
+    HAML
+
+    it { should report_lint line: 1 }
+  end
+end