Add TRYEXPAND_DEBUG_LOG CLI option

CHANGELOG.md

@@ -20,7 +20,7 @@ Please make sure to add your changes to the appropriate categories:
 
 ### Added
 
-- n/a
+- Added `TRYEXPAND_DEBUG_LOG` CLI option for turning on debug logging (use with `-- --nocapture` for optimal results).
 
 ### Changed
 

README.md

@@ -223,12 +223,28 @@ cargo +1.76.0 test <OPTIONS>
 
 For each `expand()`-like method call within your tests a temporary and uniquely named Rust project will get generated within `$CARGO_TARGET_DIR/target/tests/`.
 By default these projects will get deleted upon test completion (regardless of the outcome).
-If you wish to take a look at the actual code/projects being expanded you can provide `TRYEXPAND_KEEP_ARTIFACTS=1` (e.g. `$ TRYEXPAND_KEEP_ARTIFACTS=1 cargo test`) and `tryexpand` will skip the cleanup.
+If you wish to take a look at the actual code/projects being expanded you can provide `TRYEXPAND_KEEP_ARTIFACTS=1` and `tryexpand` will skip the cleanup:
+
+```terminal
+TRYEXPAND_KEEP_ARTIFACTS=1 cargo test
+```
 
 #### `TRYEXPAND_TRUNCATE_OUTPUT`
 
 By default `tryexpand` truncates console output that's longer than 100 lines.
-If you wish to temporarily turn this behavior you can provide `TRYEXPAND_TRUNCATE_OUTPUT=0` (e.g. `$ TRYEXPAND_TRUNCATE_OUTPUT=0 cargo test`) and `tryexpand` will produce the full console output.
+If you wish to temporarily turn this behavior you can provide `TRYEXPAND_TRUNCATE_OUTPUT=0` and `tryexpand` will produce the full console output:
+
+```terminal
+TRYEXPAND_TRUNCATE_OUTPUT=0 cargo test
+```
+
+#### `TRYEXPAND_DEBUG_LOG`
+
+If you wish to see the exact commands that `tryexpand` is executing you can provide `TRYEXPAND_DEBUG_LOG=1` (together with `--nocapture`, if you also wish to see logs of passing tests) and `tryexpand` will print additional debug logs:
+
+```terminal
+TRYEXPAND_DEBUG_LOG=0 cargo test -- --nocapture
+```
 
 ## Contributing
 

src/cargo.rs

@@ -8,6 +8,7 @@ use crate::{
     options::Options,
     project::Project,
     test::{Test, TestStatus},
+    utils::should_debug_log,
 };
 
 const RUSTFLAGS_ENV_KEY: &str = "RUSTFLAGS";
@@ -19,7 +20,6 @@ fn raw_cargo() -> Command {
 fn cargo(project: &Project) -> Command {
     let mut cmd = raw_cargo();
     cmd.current_dir(&project.dir);
-    cmd.env("CARGO_TARGET_DIR", &project.target_dir);
     cmd.env(RUSTFLAGS_ENV_KEY, make_rustflags_env());
     cmd
 }
@@ -232,13 +232,26 @@ fn run_cargo_command(mut cargo: Command, options: &Options) -> Result<CargoOutpu
         cargo.env(key, value);
     }
 
+    if should_debug_log().unwrap_or(false) {
+        println!("Command: {:?}", cargo);
+        println!("Environment: {:?}", options.envs);
+        println!();
+    }
+
     let output = cargo
         .output()
         .map_err(|err| Error::CargoExpandExecution(err.to_string()))?;
 
     let stdout = Some(String::from_utf8_lossy(&output.stdout).into_owned());
     let stderr = Some(String::from_utf8_lossy(&output.stderr).into_owned());
 
+    if should_debug_log().unwrap_or(false) {
+        println!("Stdout:\n{}", stdout.as_deref().unwrap_or("None"));
+        println!();
+        println!("Stderr:\n{}", stderr.as_deref().unwrap_or("None"));
+        println!();
+    }
+
     let evaluation = if output.status.success() {
         TestStatus::Success
     } else {

src/lib.rs

@@ -21,6 +21,7 @@ pub(crate) const TRYEXPAND_ENV_VAL_EXPECT: &str = "expect";
 
 pub(crate) const TRYEXPAND_KEEP_ARTIFACTS_ENV_KEY: &str = "TRYEXPAND_KEEP_ARTIFACTS";
 pub(crate) const TRYEXPAND_TRUNCATE_OUTPUT_ENV_KEY: &str = "TRYEXPAND_TRUNCATE_OUTPUT";
+pub(crate) const TRYEXPAND_DEBUG_LOG_ENV_KEY: &str = "TRYEXPAND_DEBUG_LOG";
 
 pub(crate) const OUT_RS_FILE_SUFFIX: &str = "out.rs";
 pub(crate) const OUT_TXT_FILE_SUFFIX: &str = "out.txt";

src/utils.rs

@@ -46,3 +46,19 @@ where
         source,
     })
 }
+
+pub(crate) fn should_debug_log() -> Result<bool> {
+    let key = crate::TRYEXPAND_DEBUG_LOG_ENV_KEY;
+    let Some(var) = std::env::var_os(key) else {
+        return Ok(false);
+    };
+    let value = var.to_string_lossy().to_lowercase().to_owned();
+    match value.as_str() {
+        "1" | "yes" | "true" => Ok(true),
+        "0" | "no" | "false" => Ok(false),
+        _ => Err(Error::UnrecognizedEnv {
+            key: key.to_owned(),
+            value,
+        }),
+    }
+}