Use cache dir for temporary files (#2067)

Sometimes `/tmp` is mounted with the `noexec` option, which results
causes running shebang recipes to fail.

Instead of `/tmp`, use the cache directory as provided by the
[dirs crate](https://docs.rs/dirs/latest/src/dirs/lib.rs.html#77).

src/error.rs

@@ -20,6 +20,10 @@ pub(crate) enum Error<'src> {
     token: Token<'src>,
     output_error: OutputError,
   },
+  CacheDirIo {
+    io_error: io::Error,
+    path: PathBuf,
+  },
   ChooserInvoke {
     shell_binary: String,
     shell_arguments: String,
@@ -279,6 +283,9 @@ impl<'src> ColorDisplay for Error<'src> {
           }?,
         OutputError::Utf8(utf8_error) => write!(f, "Backtick succeeded but stdout was not utf8: {utf8_error}")?,
       }
+      CacheDirIo { io_error, path } => {
+        write!(f, "I/O error in cache dir `{}`: {io_error}", path.display())?;
+      }
       ChooserInvoke { shell_binary, shell_arguments, chooser, io_error} => {
         let chooser = chooser.to_string_lossy();
         write!(f, "Chooser `{shell_binary} {shell_arguments} {chooser}` invocation failed: {io_error}")?;
@@ -382,8 +389,7 @@ impl<'src> ColorDisplay for Error<'src> {
         }?;
       }
       Load { io_error, path } => {
-        let path = path.display();
-        write!(f, "Failed to read justfile at `{path}`: {io_error}")?;
+        write!(f, "Failed to read justfile at `{}`: {io_error}", path.display())?;
       }
       MissingImportFile { .. } => write!(f, "Could not find source file for import.")?,
       MissingModuleFile { module } => write!(f, "Could not find source file for module `{module}`.")?,

src/recipe.rs

@@ -336,7 +336,18 @@ impl<'src, D> Recipe<'src, D> {
     tempdir_builder.prefix("just-");
     let tempdir = match &context.settings.tempdir {
       Some(tempdir) => tempdir_builder.tempdir_in(context.search.working_directory.join(tempdir)),
-      None => tempdir_builder.tempdir(),
+      None => {
+        if let Some(cache_dir) = dirs::cache_dir() {
+          let path = cache_dir.join("just");
+          fs::create_dir_all(&path).map_err(|io_error| Error::CacheDirIo {
+            io_error,
+            path: path.clone(),
+          })?;
+          tempdir_builder.tempdir_in(path)
+        } else {
+          tempdir_builder.tempdir()
+        }
+      }
     }
     .map_err(|error| Error::TempdirIo {
       recipe: self.name(),

tests/tempdir.rs

@@ -1,10 +1,18 @@
 use super::*;
 
 pub(crate) fn tempdir() -> TempDir {
-  tempfile::Builder::new()
-    .prefix("just-test-tempdir")
-    .tempdir()
-    .expect("failed to create temporary directory")
+  let mut builder = tempfile::Builder::new();
+
+  builder.prefix("just-test-tempdir");
+
+  if let Some(cache_dir) = dirs::cache_dir() {
+    let path = cache_dir.join("just");
+    fs::create_dir_all(&path).unwrap();
+    builder.tempdir_in(path)
+  } else {
+    builder.tempdir()
+  }
+  .expect("failed to create temporary directory")
 }
 
 #[test]