feat: add --simplify flag (#266)

src/bin/dts/args.rs

@@ -122,6 +122,14 @@ pub struct InputOptions {
     /// not a directory.
     #[arg(short = 'C', long, help_heading = "Input Options")]
     pub continue_on_error: bool,
+
+    /// Simplify input if the encoding supports it.
+    ///
+    /// Some encodings like HCL support partial expression evaluation, where an expression like
+    /// `1 + 2` can be evaluated to `3`. This flag controls if input simplifications like this
+    /// should be performed or not.
+    #[arg(long, help_heading = "Input Options")]
+    pub simplify: bool,
 }
 
 impl From<&InputOptions> for DeserializeOptions {
@@ -131,6 +139,7 @@ impl From<&InputOptions> for DeserializeOptions {
             csv_without_headers: opts.csv_without_headers,
             csv_delimiter: opts.csv_input_delimiter,
             text_split_pattern: opts.text_split_pattern.clone(),
+            simplify: opts.simplify,
         }
     }
 }

src/de.rs

@@ -2,6 +2,7 @@
 //! encodings into a `Value`.
 
 use crate::{key::expand_keys, parsers::gron, Encoding, Result};
+use hcl::eval::Evaluate;
 use regex::Regex;
 use serde::Deserialize;
 use serde_json::{Map, Value};
@@ -21,6 +22,8 @@ pub struct DeserializeOptions {
     pub csv_delimiter: Option<u8>,
     /// Optional regex pattern to split text input at.
     pub text_split_pattern: Option<Regex>,
+    /// Simplify input if the encoding supports it.
+    pub simplify: bool,
 }
 
 impl DeserializeOptions {
@@ -82,6 +85,12 @@ impl DeserializerBuilder {
         self
     }
 
+    /// Simplify input if the encoding supports it.
+    pub fn simplifiy(&mut self, yes: bool) -> &mut Self {
+        self.opts.simplify = yes;
+        self
+    }
+
     /// Builds the `Deserializer` for the given reader.
     pub fn build<R>(&self, reader: R) -> Deserializer<R>
     where
@@ -255,7 +264,16 @@ where
     }
 
     fn deserialize_hcl(&mut self) -> Result<Value> {
-        Ok(hcl::from_reader(&mut self.reader)?)
+        let value = if self.opts.simplify {
+            let mut body: hcl::Body = hcl::from_reader(&mut self.reader)?;
+            let ctx = hcl::eval::Context::new();
+            let _ = body.evaluate_in_place(&ctx);
+            hcl::from_body(body)?
+        } else {
+            hcl::from_reader(&mut self.reader)?
+        };
+
+        Ok(value)
     }
 }
 

tests/fixtures/math.hcl

@@ -0,0 +1,3 @@
+a = 1 + 2
+b = 3
+c = a + b

tests/fixtures/math.json

@@ -0,0 +1,5 @@
+{
+  "a": "${1 + 2}",
+  "b": 3,
+  "c": "${a + b}"
+}

tests/fixtures/math.simplified.json

@@ -0,0 +1,5 @@
+{
+  "a": 3,
+  "b": 3,
+  "c": "${a + b}"
+}

tests/integration_tests.rs

@@ -102,6 +102,28 @@ fn json_to_hcl_compact() {
         .stdout(read("tests/fixtures/example.compact.hcl").unwrap());
 }
 
+#[test]
+fn hcl_to_json() {
+    Command::cargo_bin("dts")
+        .unwrap()
+        .arg("tests/fixtures/math.hcl")
+        .args(&["-o", "json"])
+        .assert()
+        .success()
+        .stdout(read("tests/fixtures/math.json").unwrap());
+}
+
+#[test]
+fn hcl_to_json_simplified() {
+    Command::cargo_bin("dts")
+        .unwrap()
+        .arg("tests/fixtures/math.hcl")
+        .args(&["-o", "json", "--simplify"])
+        .assert()
+        .success()
+        .stdout(read("tests/fixtures/math.simplified.json").unwrap());
+}
+
 #[test]
 fn gron_to_json() {
     Command::cargo_bin("dts")