new: flag rust-toolchain.toml pins in pkh new

src/new/questions.rs

@@ -160,6 +160,22 @@ async fn run_wizard(mut cli: NewCli) -> Result<NewOptions, Box<dyn Error>> {
     }
     let template = TemplateId::parse(cli.lang.as_deref().unwrap_or_default())?;
 
+    // The rust toolchain pin of the packaged project does not travel into
+    // the chroot build: surface it now so a too-old pin is not a surprise
+    // when `pkh deb` compiles with the distribution's rustc.
+    let toolchain_pin = if template == TemplateId::Rust {
+        probe.as_ref().and_then(|p| p.toolchain_pin.clone())
+    } else {
+        None
+    };
+    if let Some(pin) = &toolchain_pin {
+        log::info!(
+            "Project pins rust {pin} via rust-toolchain.toml; the chroot \
+             build uses the distribution's rustc and ignores the pin — \
+             adjust or remove it if the code needs newer compiler features"
+        );
+    }
+
     // 3. Source location. Skipped (with the inline notice) when a confident
     //    detection already decided to package the current directory; a
     //    --source flag skips it too.
@@ -398,7 +414,7 @@ async fn run_wizard(mut cli: NewCli) -> Result<NewOptions, Box<dyn Error>> {
 
     // Summary screen + final confirmation: Ctrl+C or 'n' abort with
     // nothing written (generation is all-or-nothing later anyway).
-    println!("{}", summary_text(&opts));
+    println!("{}", summary_text(&opts, toolchain_pin.as_deref()));
     if !prompt::confirm("Generate?", true)? {
         return Err("Aborted: nothing was written to disk.".into());
     }
@@ -714,12 +730,13 @@ pub fn watch_template(homepage: Option<&str>) -> Option<String> {
     ))
 }
 
-/// The summary screen shown before the final `Generate?` confirmation
-/// (spec transcript): identity line, template/license/maintainer line, the
-/// generated-file overview and — for a metapackage — the Depends payload,
-/// for a skeleton — the upstream files that will be created, and for rust —
-/// a warning when dependencies cannot be vendored on this host.
-pub fn summary_text(opts: &NewOptions) -> String {
+/// The pre-flight summary screen shown before the final `Generate?`
+/// confirmation (spec transcript): identity line, template/license/maintainer
+/// line, the generated-file overview and — for a metapackage — the Depends
+/// payload, for a skeleton — the upstream files that will be created, and
+/// for rust — the probed toolchain pin (when any; the chroot build ignores
+/// it) plus a warning when dependencies cannot be vendored on this host.
+pub fn summary_text(opts: &NewOptions, toolchain_pin: Option<&str>) -> String {
     let template = templates::get(opts.template);
     let mut lines = Vec::new();
 
@@ -756,6 +773,13 @@ pub fn summary_text(opts: &NewOptions) -> String {
                 "  debian/rules      cargo build --release --offline (vendored at generation)"
                     .to_string(),
             );
+            // A pinned rust-toolchain.toml does not reach the chroot build:
+            // flagged here so a too-old pin is no surprise later.
+            if let Some(pin) = toolchain_pin {
+                lines.push(format!(
+                    "  rust-toolchain    {pin} (ignored by the chroot build)"
+                ));
+            }
         } else {
             lines.push(format!("  debian/rules      {}", template.rules_dh_line()));
         }
@@ -923,7 +947,7 @@ mod tests {
 
     #[test]
     fn summary_screen_skeleton() {
-        let text = summary_text(&opts(Tid::Makefile));
+        let text = summary_text(&opts(Tid::Makefile), None);
         assert!(
             text.contains("mytool 0.1.0-1 · builds for ubuntu/resolute"),
             "{text}"
@@ -956,7 +980,7 @@ mod tests {
         let mut o = opts(Tid::Empty);
         o.depends = vec!["hello".to_string(), "hello-data (>= 1.0)".to_string()];
         o.source_dir = options::SourceDir::Here;
-        let text = summary_text(&o);
+        let text = summary_text(&o, None);
         assert!(text.contains("Architecture: all"), "{text}");
         assert!(
             text.contains("Depends           hello, hello-data (>= 1.0)"),
@@ -973,7 +997,7 @@ mod tests {
         o.release = true;
         o.autopkgtest = true;
         o.watch = Some("version=4\n".to_string());
-        let text = summary_text(&o);
+        let text = summary_text(&o, None);
         assert!(text.contains("0.1.0-1 resolute, Initial release"), "{text}");
         assert!(
             text.contains("debian/tests      autopkgtest smoke test"),
@@ -987,7 +1011,7 @@ mod tests {
     /// yet (regression: it claimed "(vendored)" before generating).
     #[test]
     fn summary_screen_rust_does_not_presume_vendoring() {
-        let text = summary_text(&opts(Tid::Rust));
+        let text = summary_text(&opts(Tid::Rust), None);
         assert!(
             text.contains("cargo build --release --offline (vendored at generation)"),
             "{text}"
@@ -995,6 +1019,23 @@ mod tests {
         assert!(!text.contains("(vendored)"), "{text}");
     }
 
+    /// A probed rust toolchain pin surfaces in the summary as its own row
+    /// (rust template only), flagged as ignored by the chroot build.
+    #[test]
+    fn summary_screen_shows_the_toolchain_pin() {
+        let text = summary_text(&opts(Tid::Rust), Some("1.98.0"));
+        assert!(
+            text.contains("rust-toolchain    1.98.0 (ignored by the chroot build)"),
+            "{text}"
+        );
+
+        // No pin, no row.
+        assert!(!summary_text(&opts(Tid::Rust), None).contains("rust-toolchain"));
+        // A pin under a template other than rust is not shown either (the
+        // pin only matters for a cargo build).
+        assert!(!summary_text(&opts(Tid::Go), Some("1.98.0")).contains("rust-toolchain"));
+    }
+
     #[test]
     fn answer_validators() {
         assert!(validate_revision_answer("1").is_ok());

src/new/templates/mod.rs

@@ -81,6 +81,11 @@ pub struct ProbeResult {
     /// Installed command / binary name (e.g. the first `[[bin]]` target or
     /// console script).
     pub command: Option<String>,
+    /// Rust toolchain channel pinned by the project's `rust-toolchain.toml`
+    /// (or legacy `rust-toolchain`), e.g. `1.98.0`. Only set by the rust
+    /// template; the chroot build uses the distribution's rustc and ignores
+    /// the pin, so the wizard surfaces it as a heads-up instead.
+    pub toolchain_pin: Option<String>,
 }
 
 /// A package template: one supported ecosystem / build system.

src/new/templates/python.rs

@@ -208,6 +208,7 @@ impl Template for Python {
                 homepage: project.homepage,
                 license: project.license,
                 command: project.script,
+                ..Default::default()
             };
             if result.name.is_some()
                 || result.version.is_some()

src/new/templates/rust.rs

@@ -118,12 +118,24 @@ impl Template for Rust {
 
     /// Name, version, description, homepage, license and first binary from
     /// `cargo metadata --no-deps` (when host cargo is available), with a
-    /// minimal line-parse of `Cargo.toml` as fallback.
+    /// minimal line-parse of `Cargo.toml` as fallback; plus the toolchain
+    /// channel pinned by `rust-toolchain.toml` / legacy `rust-toolchain`.
     fn probe(&self, dir: &Path) -> Option<ProbeResult> {
-        if let Some(result) = probe_cargo_metadata(dir) {
-            return Some(result);
+        match probe_cargo_metadata(dir).or_else(|| probe_cargo_toml(dir)) {
+            Some(mut result) => {
+                result.toolchain_pin = toolchain_pin(dir);
+                Some(result)
+            }
+            // A Cargo.toml that resists reading, but a toolchain pin this
+            // template can still report.
+            None => {
+                let pin = toolchain_pin(dir)?;
+                Some(ProbeResult {
+                    toolchain_pin: Some(pin),
+                    ..Default::default()
+                })
+            }
         }
-        probe_cargo_toml(dir)
     }
 
     /// Vendor the Cargo dependencies into the freshly written tree: run
@@ -360,6 +372,8 @@ fn probe_cargo_metadata(dir: &Path) -> Option<ProbeResult> {
         homepage: field("homepage"),
         license: field("license"),
         command,
+        // Filled in by `probe` from the rust-toolchain file, not metadata.
+        toolchain_pin: None,
     })
 }
 
@@ -401,6 +415,56 @@ fn probe_cargo_toml(dir: &Path) -> Option<ProbeResult> {
     }
 }
 
+/// The rust toolchain channel pinned in `dir`: `rust-toolchain.toml`
+/// (preferred, like rustup does) or the legacy bare `rust-toolchain`.
+/// `None` without a pin file or when it names no channel.
+fn toolchain_pin(dir: &Path) -> Option<String> {
+    let content = std::fs::read_to_string(dir.join("rust-toolchain.toml"))
+        .or_else(|_| std::fs::read_to_string(dir.join("rust-toolchain")))
+        .ok()?;
+    parse_toolchain_channel(&content)
+}
+
+/// Minimal line-parse of the `channel` out of a `rust-toolchain` file (no
+/// TOML dependency, matching the `Cargo.toml` fallback above):
+/// `channel = "…"` (single quotes work too) under the `[toolchain]` section,
+/// comments and unrelated sections tolerated. Without a parseable TOML
+/// channel, a legacy bare `rust-toolchain` — just the channel string on a
+/// single line, no TOML syntax at all — is taken whole.
+fn parse_toolchain_channel(content: &str) -> Option<String> {
+    let mut in_toolchain = false;
+    for line in content.lines() {
+        let line = line.trim();
+        if line.is_empty() || line.starts_with('#') {
+            continue;
+        }
+        if let Some(header) = line.strip_prefix('[').and_then(|l| l.strip_suffix(']')) {
+            in_toolchain = header.trim() == "toolchain";
+            continue;
+        }
+        if !in_toolchain {
+            continue;
+        }
+        if let Some((key, value)) = line.split_once('=')
+            && key.trim() == "channel"
+        {
+            let value = value.trim().trim_matches('"').trim_matches('\'').trim();
+            if !value.is_empty() {
+                return Some(value.to_string());
+            }
+        }
+    }
+    // Legacy bare format: the whole file is the channel name (never
+    // comment-only).
+    let bare = content.trim();
+    (!bare.is_empty()
+        && !bare.starts_with('#')
+        && !bare.contains('\n')
+        && !bare.contains('=')
+        && !bare.contains('['))
+    .then(|| bare.to_string())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -713,4 +777,106 @@ mod tests {
             None => unsafe { std::env::remove_var("RUSTUP_TOOLCHAIN") },
         }
     }
+
+    /// The `rust-toolchain` channel parser: quoted channel under
+    /// `[toolchain]` (double or single quotes, with comments and unrelated
+    /// sections around), the legacy bare single-line format taken whole, and
+    /// the failure cases (missing key, empty channel, wrong section, empty
+    /// file).
+    #[test]
+    fn parse_toolchain_channel_variants() {
+        // The canonical spelling.
+        assert_eq!(
+            parse_toolchain_channel("[toolchain]\nchannel = \"1.98.0\"\n"),
+            Some("1.98.0".to_string())
+        );
+        // Single quotes, no trailing newline, no spaces around `=`.
+        assert_eq!(
+            parse_toolchain_channel("[toolchain]\nchannel='nightly'"),
+            Some("nightly".to_string())
+        );
+        // Comments, blank lines and unrelated sections tolerated.
+        assert_eq!(
+            parse_toolchain_channel(
+                "# pin for CI\n\
+                 \n\
+                 [toolchain]\n\
+                 # bumped by cargo update\n\
+                 channel = \"stable\"\n\
+                 \n\
+                 [targets.x86_64-unknown-linux-gnu]\n"
+            ),
+            Some("stable".to_string())
+        );
+        // Legacy bare `rust-toolchain`: just the channel string, no TOML.
+        assert_eq!(
+            parse_toolchain_channel("1.98.0\n"),
+            Some("1.98.0".to_string())
+        );
+        assert_eq!(
+            parse_toolchain_channel("nightly"),
+            Some("nightly".to_string())
+        );
+        // Missing channel key.
+        assert_eq!(
+            parse_toolchain_channel("[toolchain]\ncomponents = [\"rustfmt\"]\n"),
+            None
+        );
+        // Wrong section: the key is not honored (rustup would ignore it too).
+        assert_eq!(
+            parse_toolchain_channel("[unstable]\nchannel = \"1.98.0\"\n"),
+            None
+        );
+        // Empty channel value or file: nothing to report.
+        assert_eq!(
+            parse_toolchain_channel("[toolchain]\nchannel = \"\"\n"),
+            None
+        );
+        assert_eq!(parse_toolchain_channel(""), None);
+        assert_eq!(parse_toolchain_channel("# only a comment\n"), None);
+    }
+
+    /// `probe()` carries the pin next to the project metadata:
+    /// `rust-toolchain.toml` wins over the legacy file (as with rustup), and
+    /// no pin file leaves the field empty.
+    #[test]
+    fn probe_reports_the_toolchain_pin() {
+        let template = super::super::get(TemplateId::Rust).unwrap();
+        let cargo_toml = "[package]\nname = \"pinned\"\nversion = \"1.0.0\"\n";
+
+        let dir = tempdir().unwrap();
+        std::fs::write(dir.path().join("Cargo.toml"), cargo_toml).unwrap();
+        std::fs::write(
+            dir.path().join("rust-toolchain.toml"),
+            "[toolchain]\nchannel = \"1.98.0\"\n",
+        )
+        .unwrap();
+        let probe = template.probe(dir.path()).expect("probe result");
+        assert_eq!(probe.name.as_deref(), Some("pinned"));
+        assert_eq!(probe.toolchain_pin.as_deref(), Some("1.98.0"));
+
+        // The legacy bare file is honored when there is no toml ...
+        let dir = tempdir().unwrap();
+        std::fs::write(dir.path().join("Cargo.toml"), cargo_toml).unwrap();
+        std::fs::write(dir.path().join("rust-toolchain"), "nightly\n").unwrap();
+        assert_eq!(
+            template.probe(dir.path()).unwrap().toolchain_pin,
+            Some("nightly".to_string())
+        );
+        // ... but loses once the toml exists.
+        std::fs::write(
+            dir.path().join("rust-toolchain.toml"),
+            "[toolchain]\nchannel = \"1.90.0\"\n",
+        )
+        .unwrap();
+        assert_eq!(
+            template.probe(dir.path()).unwrap().toolchain_pin,
+            Some("1.90.0".to_string())
+        );
+
+        // No pin file at all.
+        let dir = tempdir().unwrap();
+        std::fs::write(dir.path().join("Cargo.toml"), cargo_toml).unwrap();
+        assert_eq!(template.probe(dir.path()).unwrap().toolchain_pin, None);
+    }
 }