fix: check for git presence before calling

This follows up #647 by also ensuring we don't call `git` if it's
not present on the system. If it's missing, we skip trying to
generate a source tarball altogether.

cargo-dist/src/errors.rs

@@ -266,6 +266,14 @@ pub enum DistError {
     #[error("We failed to generate a source tarball for your project")]
     #[diagnostic(help("This is probably not your fault, please file an issue!"))]
     GitArchiveError {},
+
+    /// A required tool is missing
+    #[error("{tool}, required to run this task, is missing")]
+    #[diagnostic(help("Ensure {tool} is installed"))]
+    ToolMissing {
+        /// the name of the missing tool
+        tool: String,
+    },
 }
 
 impl From<minijinja::Error> for DistError {

cargo-dist/src/lib.rs

@@ -137,7 +137,9 @@ fn run_build_step(
             committish,
             prefix,
             target,
-        }) => Ok(generate_source_tarball(committish, prefix, target)?),
+        }) => Ok(generate_source_tarball(
+            dist_graph, committish, prefix, target,
+        )?),
         BuildStep::Extra(target) => run_extra_artifacts_build(dist_graph, target),
     }
 }
@@ -185,8 +187,21 @@ fn generate_checksum(checksum: &ChecksumStyle, src_path: &Utf8Path) -> DistResul
 /// Creates a source code tarball from the git archive from
 /// tag/ref/commit `committish`, with the directory prefix `prefix`,
 /// at the output file `target`.
-fn generate_source_tarball(committish: &str, prefix: &str, target: &Utf8Path) -> DistResult<()> {
-    let status = Command::new("git")
+fn generate_source_tarball(
+    graph: &DistGraph,
+    committish: &str,
+    prefix: &str,
+    target: &Utf8Path,
+) -> DistResult<()> {
+    let git = if let Some(tool) = &graph.tools.git {
+        tool.cmd.to_owned()
+    } else {
+        return Err(DistError::ToolMissing {
+            tool: "git".to_owned(),
+        });
+    };
+
+    let status = Command::new(git)
         .arg("archive")
         .arg(committish)
         .arg("--format=tar.gz")

cargo-dist/src/tasks.rs

@@ -235,6 +235,8 @@ pub struct Tools {
     pub rustup: Option<Tool>,
     /// homebrew, only available on macOS
     pub brew: Option<Tool>,
+    /// git, used if the repository is a git repo
+    pub git: Option<Tool>,
 }
 
 /// Info about the cargo toolchain we're using
@@ -1202,13 +1204,20 @@ impl<'pkg_graph> DistGraphBuilder<'pkg_graph> {
             return;
         }
 
+        let git = if let Some(tool) = &self.inner.tools.git {
+            tool.cmd.to_owned()
+        } else {
+            warn!("skipping source tarball; git not installed");
+            return;
+        };
+
         // It's possible to run cargo-dist in something that's not a git
         // repo, including a brand-new repo that hasn't been `git init`ted yet;
         // we can't act on those.
         //
         // Note we don't need the output of --show-toplevel,
         // just the exit status.
-        let status = Command::new("git")
+        let status = Command::new(git)
             .arg("rev-parse")
             .arg("--show-toplevel")
             .stdout(std::process::Stdio::piped())
@@ -2679,6 +2688,7 @@ fn tool_info() -> Result<Tools> {
         cargo,
         rustup: find_tool("rustup", "-V"),
         brew: find_tool("brew", "--version"),
+        git: find_tool("git", "--version"),
     })
 }
 

cargo-dist/src/tests/mock.rs

@@ -48,6 +48,7 @@ pub fn mock_tools() -> Tools {
         },
         rustup: None,
         brew: None,
+        git: None,
     }
 }