From 40d855d3ed00ef448ceb90bbbf25fa1115538f01 Mon Sep 17 00:00:00 2001
From: moe <moe@busyloop.net>
Date: Tue, 26 Mar 2024 23:12:53 +0100
Subject: [PATCH] Improve jinja2 error handling

---
 spec/envcat/cli/format/j2_spec.cr |  9 +++++++++
 src/envcat/cli.cr                 |  2 +-
 src/envcat/format/j2.cr           | 27 +++++++++++++++++----------
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/spec/envcat/cli/format/j2_spec.cr b/spec/envcat/cli/format/j2_spec.cr
index 790497b..90f7a6a 100644
--- a/spec/envcat/cli/format/j2_spec.cr
+++ b/spec/envcat/cli/format/j2_spec.cr
@@ -14,6 +14,15 @@ describe Envcat::Cli do
       }
     end
 
+    it "fails cleanly on 'empty expression' template error" do
+      tpl = "{{}}"
+      expect_output(/^$/, /^Malformed template:/, tpl) { |o, e, i|
+        expect_raises(Exit, "3") {
+          Envcat::Cli.invoke(%w[-f j2], o, e, i)
+        }
+      }
+    end
+
     it "fails if any referenced var is undefined" do
       tpl = "{{FOO}} {{BAR}}"
       expect_output(/^$/, /Undefined variable: BAR/, tpl) { |o, e, i|
diff --git a/src/envcat/cli.cr b/src/envcat/cli.cr
index b3ad88d..e7e9ba4 100644
--- a/src/envcat/cli.cr
+++ b/src/envcat/cli.cr
@@ -225,7 +225,7 @@ class Envcat::Cli
   rescue ex : Format::UnknownFormatIdError
     io_err.puts "Unknown format: #{ex.message}"
     exit E_SYNTAX
-  rescue ex : Crinja::TemplateSyntaxError | Crinja::FeatureLibrary::UnknownFeatureError | Crinja::TypeError
+  rescue ex : Crinja::TemplateSyntaxError | Crinja::FeatureLibrary::UnknownFeatureError | Crinja::TypeError | Format::J2::RenderError
     io_err.puts "Malformed template: #{ex.message}"
     exit E_SYNTAX
   rescue ex : ParseException
diff --git a/src/envcat/format/j2.cr b/src/envcat/format/j2.cr
index 7a2942b..7c6bf49 100644
--- a/src/envcat/format/j2.cr
+++ b/src/envcat/format/j2.cr
@@ -3,7 +3,7 @@ require "crinja"
 
 # 🐒
 class Crinja::Undefined
-  class_property strict = false # ameba:disable Style/QueryBoolMethods
+  class_property strict = false # ameba:disable Naming/QueryBoolMethods
   class_property tagged = [] of String
 
   def to_s(io)
@@ -24,6 +24,8 @@ module Envcat
   class Format::J2 < Format::Formatter
     class UndefinedVariableError < Exception; end
 
+    class RenderError < Exception; end
+
     @@strict = true
 
     def self.description : String
@@ -37,18 +39,23 @@ module Envcat
     def write(env)
       Envcat.claim_stdin! if @io_in == STDIN
 
-      Crinja::Undefined.strict = @@strict
+      begin
+        Crinja::Undefined.strict = @@strict
 
-      crinja = Crinja.new(Crinja::Config.new(keep_trailing_newline: true))
+        crinja = Crinja.new(Crinja::Config.new(keep_trailing_newline: true))
 
-      crinja.filters["split"] = Crinja.filter({on: nil}) { target.to_s.split(arguments["on"].to_s) }
-      crinja.filters["b64encode"] = Crinja.filter { Base64.strict_encode(target.to_s) }
-      crinja.filters["b64encode_urlsafe"] = Crinja.filter { Base64.urlsafe_encode(target.to_s) }
-      crinja.filters["b64decode"] = Crinja.filter { Base64.decode_string(target.to_s) }
+        crinja.filters["split"] = Crinja.filter({on: nil}) { target.to_s.split(arguments["on"].to_s) }
+        crinja.filters["b64encode"] = Crinja.filter { Base64.strict_encode(target.to_s) }
+        crinja.filters["b64encode_urlsafe"] = Crinja.filter { Base64.urlsafe_encode(target.to_s) }
+        crinja.filters["b64decode"] = Crinja.filter { Base64.decode_string(target.to_s) }
 
-      buf = IO::Memory.new(16384)
-      IO.copy(@io_in, buf)
-      crinja.from_string(buf.to_s).render(@io, env.as(Envcat::Env))
+        buf = IO::Memory.new(16384)
+        IO.copy(@io_in, buf)
+        crinja.from_string(buf.to_s).render(@io, env.as(Envcat::Env))
+      rescue ex
+        raise ex if ex.is_a? Format::J2::UndefinedVariableError
+        raise RenderError.new(ex.message)
+      end
     end
   end
 end