cli: conventionally treat - as "read from stdin" (#1314)

Basically, when a path to a requirements file is `-`, then we should
read its contents from `stdin` instead of the file path named `-`.

Fixes #1313

crates/puffin-fs/src/lib.rs

@@ -12,6 +12,38 @@ pub use crate::path::*;
 
 mod path;
 
+/// Reads the contents of the file path given into memory.
+///
+/// If the file path is `-`, then contents are read from stdin instead.
+pub fn read(path: impl AsRef<Path>) -> std::io::Result<Vec<u8>> {
+    use std::io::Read;
+
+    let path = path.as_ref();
+    if path == Path::new("-") {
+        let mut buf = Vec::with_capacity(1024);
+        std::io::stdin().read_to_end(&mut buf)?;
+        Ok(buf)
+    } else {
+        fs::read(path)
+    }
+}
+
+/// Reads the contents of the file path given into memory as a `String`.
+///
+/// If the file path is `-`, then contents are read from stdin instead.
+pub fn read_to_string(path: impl AsRef<Path>) -> std::io::Result<String> {
+    use std::io::Read;
+
+    let path = path.as_ref();
+    if path == Path::new("-") {
+        let mut buf = String::with_capacity(1024);
+        std::io::stdin().read_to_string(&mut buf)?;
+        Ok(buf)
+    } else {
+        fs::read_to_string(path)
+    }
+}
+
 /// Create a symlink from `src` to `dst`, replacing any existing symlink.
 ///
 /// On Windows, this uses the `junction` crate to create a junction point.

crates/puffin/src/main.rs

@@ -158,6 +158,8 @@ fn date_or_datetime(input: &str) -> Result<DateTime<Utc>, String> {
 #[allow(clippy::struct_excessive_bools)]
 struct PipCompileArgs {
     /// Include all packages listed in the given `requirements.in` files.
+    ///
+    /// When the path is `-`, then requirements are read from stdin.
     #[clap(required(true))]
     src_file: Vec<PathBuf>,
 

crates/puffin/src/requirements.rs

@@ -4,7 +4,6 @@ use std::path::{Path, PathBuf};
 
 use anyhow::{Context, Result};
 use console::Term;
-use fs_err as fs;
 use rustc_hash::FxHashSet;
 
 use distribution_types::{FlatIndexLocation, IndexUrl};
@@ -193,7 +192,7 @@ impl RequirementsSpecification {
                 }
             }
             RequirementsSource::PyprojectToml(path) => {
-                let contents = fs::read_to_string(path)?;
+                let contents = puffin_fs::read_to_string(path)?;
                 let pyproject_toml = toml::from_str::<pyproject_toml::PyProjectToml>(&contents)
                     .with_context(|| format!("Failed to parse `{}`", path.normalized_display()))?;
                 let mut used_extras = FxHashSet::default();

crates/puffin/tests/pip_compile.rs

@@ -47,6 +47,36 @@ fn compile_requirements_in() -> Result<()> {
     Ok(())
 }
 
+/// Resolve a specific version of Django from a `requirements.in` file on stdin
+/// when passed a path of `-`.
+#[test]
+fn compile_requirements_in_stdin() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("django==5.0b1")?;
+
+    puffin_snapshot!(context
+        .compile()
+        .stdin(fs::File::open(requirements_in)?)
+        .arg("-"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by Puffin v[VERSION] via the following command:
+    #    puffin pip compile --cache-dir [CACHE_DIR] --exclude-newer 2023-11-18T12:00:00Z -
+    asgiref==3.7.2
+        # via django
+    django==5.0b1
+    sqlparse==0.4.4
+        # via django
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    Ok(())
+}
+
 #[test]
 fn missing_requirements_in() {
     let context = TestContext::new("3.12");

crates/requirements-txt/src/lib.rs

@@ -39,7 +39,6 @@ use std::fmt::{Display, Formatter};
 use std::io;
 use std::path::{Path, PathBuf};
 
-use fs_err as fs;
 use serde::{Deserialize, Serialize};
 use tracing::warn;
 use unscanny::{Pattern, Scanner};
@@ -299,10 +298,11 @@ impl RequirementsTxt {
         requirements_txt: impl AsRef<Path>,
         working_dir: impl AsRef<Path>,
     ) -> Result<Self, RequirementsTxtFileError> {
-        let content =
+        let content = puffin_fs::read_to_string(&requirements_txt).map_err(|err| {
-            fs::read_to_string(&requirements_txt).map_err(|err| RequirementsTxtFileError {
+            RequirementsTxtFileError {
                 file: requirements_txt.as_ref().to_path_buf(),
                 error: RequirementsTxtParserError::IO(err),
+            }
         })?;
         let data = Self::parse_inner(&content, working_dir.as_ref()).map_err(|err| {
             RequirementsTxtFileError {