Make #each handle non-iterable values like the original JavaScript version #380

mkantor · 2020-09-07T16:51:22Z

Previously things like {{#each "foo"}} were render errors. Now non-iterable values are treated like empty iterables. This brings handlebars-rust's behavior closer in line with the original JavaScript library.

Previously things like `{{#each "foo"}}` were render errors. Now non-iterable values are treated like empty iterables. This brings handlebars-rust's behavior closer in line with the original JavaScript library. Here are the two new test cases in the handlebars playground: 1. https://handlebarsjs.com/playground.html#format=1&currentExample=%7B%22template%22%3A%22%7B%7B%23each%20this%7D%7Deach%20block%7B%7Belse%7D%7Delse%20block%7B%7B%2Feach%7D%7D%22%2C%22partials%22%3A%5B%5D%2C%22input%22%3A%22%5C%22strings%20aren't%20iterable%5C%22%22%2C%22output%22%3A%22else%20block%22%2C%22preparationScript%22%3A%22%22%2C%22handlebarsVersion%22%3A%224.7.6%22%7D 2. https://handlebarsjs.com/playground.html#format=1&currentExample=%7B%22template%22%3A%22%7B%7B%23*inline%20%5C%22walk%5C%22%7D%7D(%7B%7B%23each%20this%7D%7D%7B%7B%23if%20%40key%7D%7D%7B%7B%40key%7D%7D%7B%7Belse%7D%7D%7B%7B%40index%7D%7D%7B%7B%2Fif%7D%7D%3A%20%7B%7Bthis%7D%7D%20%7B%7B%3E%20walk%20this%7D%7D%2C%20%7B%7B%2Feach%7D%7D)%7B%7B%2Finline%7D%7D%5Cn%7B%7B%3E%20walk%7D%7D%22%2C%22partials%22%3A%5B%5D%2C%22input%22%3A%22%7B%5Cn%20%20%20%20%5C%22array%5C%22%3A%20%5B42%2C%20%7B%5C%22wow%5C%22%3A%20%5C%22cool%5C%22%7D%2C%20%5B%5B%5D%5D%5D%2C%5Cn%20%20%20%20%5C%22object%5C%22%3A%20%7B%20%5C%22a%5C%22%3A%20%7B%20%5C%22b%5C%22%3A%20%5C%22c%5C%22%2C%20%5C%22d%5C%22%3A%20%5B%5C%22e%5C%22%5D%20%7D%20%7D%2C%5Cn%20%20%20%20%5C%22string%5C%22%3A%20%5C%22hi%5C%22%5Cn%7D%22%2C%22output%22%3A%22%5Cn(array%3A%2042%2C%5Bobject%20Object%5D%2C%20(0%3A%2042%20()%2C%201%3A%20%5Bobject%20Object%5D%20(wow%3A%20cool%20()%2C%20)%2C%202%3A%20%20(0%3A%20%20()%2C%20)%2C%20)%2C%20object%3A%20%5Bobject%20Object%5D%20(a%3A%20%5Bobject%20Object%5D%20(b%3A%20c%20()%2C%20d%3A%20e%20(0%3A%20e%20()%2C%20)%2C%20)%2C%20)%2C%20string%3A%20hi%20()%2C%20)%22%2C%22preparationScript%22%3A%22%22%2C%22handlebarsVersion%22%3A%224.7.6%22%7D

mkantor · 2020-09-07T16:51:38Z

src/helpers/helper_each.rs

+        let input = json!("strings aren't iterable");
+        let rendered = reg.render_template(template, &input).unwrap();
+        assert_eq!("else block", rendered);
+    }


Compatibility check.

mkantor · 2020-09-07T16:51:55Z

src/helpers/helper_each.rs

+
+        let rendered = reg.render("walk", &input).unwrap();
+        assert_eq!(expected_output, rendered);
+    }


Compatibility check.

The output of this one differs slightly, but only because handlebars-rust stringifies objects and arrays in its own way (FWIW I like the handlebars-rust stringifications better).

Recursion was my main motivation behind this pull request, by the way. I couldn't recursively iterate through data structures because handlebars-rust would error on the first non-iterable value it encountered.

mkantor · 2020-09-07T16:57:42Z

It doesn't change the behavior, but I think this additional tweak improves readability a bit:

diff --git a/src/helpers/helper_each.rs b/src/helpers/helper_each.rs
index 0814360..8137f2d 100644
--- a/src/helpers/helper_each.rs
+++ b/src/helpers/helper_each.rs
@@ -5,7 +5,7 @@ use crate::block::{BlockContext, BlockParams};
 use crate::context::Context;
 use crate::error::RenderError;
 use crate::helpers::{HelperDef, HelperResult};
-use crate::json::value::{to_json, JsonTruthy};
+use crate::json::value::to_json;
 use crate::output::Output;
 use crate::registry::Registry;
 use crate::render::{Helper, RenderContext, Renderable};
@@ -79,8 +79,8 @@ impl HelperDef for EachHelper {
         let template = h.template();
 
         match template {
-            Some(t) => match (value.value().is_truthy(false), value.value()) {
-                (true, &Json::Array(ref list)) => {
+            Some(t) => match value.value() {
+                &Json::Array(ref list) if !list.is_empty() => {
                     let block_context = create_block(&value)?;
                     rc.push_block(block_context);
 
@@ -108,7 +108,7 @@ impl HelperDef for EachHelper {
                     rc.pop_block();
                     Ok(())
                 }
-                (true, &Json::Object(ref obj)) => {
+                &Json::Object(ref obj) if !obj.is_empty() => {
                     let block_context = create_block(&value)?;
                     rc.push_block(block_context);

Let me know if you like it and I'll push another commit.

sunng87 · 2020-09-08T14:48:52Z

Thank you very much. This is great addition!

sunng87

It seems we can remove the truthy check in https://github.com/sunng87/handlebars-rust/pull/380/files#diff-6f7f1fa0fa8cb634e6e7d062be921ac8L82 because else will be rendered for any case that non-iterable

Update: #380 (comment) is welcomed

sunng87 · 2020-09-08T14:56:13Z

It doesn't change the behavior, but I think this additional tweak improves readability a bit:

diff --git a/src/helpers/helper_each.rs b/src/helpers/helper_each.rs
index 0814360..8137f2d 100644
--- a/src/helpers/helper_each.rs
+++ b/src/helpers/helper_each.rs
@@ -5,7 +5,7 @@ use crate::block::{BlockContext, BlockParams};
 use crate::context::Context;
 use crate::error::RenderError;
 use crate::helpers::{HelperDef, HelperResult};
-use crate::json::value::{to_json, JsonTruthy};
+use crate::json::value::to_json;
 use crate::output::Output;
 use crate::registry::Registry;
 use crate::render::{Helper, RenderContext, Renderable};
@@ -79,8 +79,8 @@ impl HelperDef for EachHelper {
         let template = h.template();
 
         match template {
-            Some(t) => match (value.value().is_truthy(false), value.value()) {
-                (true, &Json::Array(ref list)) => {
+            Some(t) => match value.value() {
+                &Json::Array(ref list) if !list.is_empty() => {
                     let block_context = create_block(&value)?;
                     rc.push_block(block_context);
 
@@ -108,7 +108,7 @@ impl HelperDef for EachHelper {
                     rc.pop_block();
                     Ok(())
                 }
-                (true, &Json::Object(ref obj)) => {
+                &Json::Object(ref obj) if !obj.is_empty() => {
                     let block_context = create_block(&value)?;
                     rc.push_block(block_context);

Let me know if you like it and I'll push another commit.

Just saw this. I'm +1 for it. Also the if check in pattern matching is new to me.

mkantor · 2020-09-08T17:30:13Z

Thanks for taking a look! I pushed ~~578590a~~ 5930fdd (clippy had a suggestion so I amended the commit) with the readability improvement from #380 (comment).

the if check in pattern matching is new to me

FYI they're called match guards and can be pretty handy, although a downside is the compiler doesn't check them for exhaustiveness like it does with unguarded matches (not a problem here since we have a _ case).

…rable-values Make #each handle non-iterable values like the original JavaScript version

mkantor commented Sep 7, 2020

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sunng87 reviewed Sep 8, 2020

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Readability improvement for #each.

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5930fdd

mkantor force-pushed the compat-each-should-allow-non-iterable-values branch from 578590a to 5930fdd Compare September 8, 2020 17:35

sunng87 approved these changes Sep 9, 2020

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sunng87 merged commit 6b11126 into sunng87:master Sep 9, 2020

mkantor deleted the compat-each-should-allow-non-iterable-values branch September 18, 2020 18:31

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Make #each handle non-iterable values like the original JavaScript version #380

Make #each handle non-iterable values like the original JavaScript version #380

mkantor commented Sep 7, 2020

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Make #each handle non-iterable values like the original JavaScript version #380

Make #each handle non-iterable values like the original JavaScript version #380

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