Hint git-fetch-with-cli on git errors

src/cargo/sources/git/utils.rs

@@ -4,7 +4,7 @@ use crate::util::paths;
 use crate::util::process_builder::process;
 use crate::util::{network, Config, IntoUrl, Progress};
 use curl::easy::{Easy, List};
-use git2::{self, ObjectType};
+use git2::{self, ErrorClass, ObjectType};
 use log::{debug, info};
 use serde::ser;
 use serde::Serialize;
@@ -97,10 +97,43 @@ impl GitRemote {
         reference: &GitReference,
         cargo_config: &Config,
     ) -> CargoResult<(GitDatabase, GitRevision)> {
+        let format_error = |e: anyhow::Error, operation| {
+            let may_be_libgit_fault = e
+                .chain()
+                .filter_map(|e| e.downcast_ref::<git2::Error>())
+                .any(|e| match e.class() {
+                    ErrorClass::Net
+                    | ErrorClass::Ssl
+                    | ErrorClass::Submodule
+                    | ErrorClass::FetchHead
+                    | ErrorClass::Ssh
+                    | ErrorClass::Callback
+                    | ErrorClass::Http => true,
+                    _ => false,
+                });
+            let uses_cli = cargo_config
+                .net_config()
+                .ok()
+                .and_then(|config| config.git_fetch_with_cli)
+                .unwrap_or(false);
+            let msg = if !uses_cli && may_be_libgit_fault {
+                format!(
+                    r"failed to {} into: {}
+  If your environment requires git authentication or proxying, try enabling `git-fetch-with-cli`
+  https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli",
+                    operation,
+                    into.display()
+                )
+            } else {
+                format!("failed to {} into: {}", operation, into.display())
+            };
+            e.context(msg)
+        };
+
         let mut repo_and_rev = None;
         if let Ok(mut repo) = git2::Repository::open(into) {
             self.fetch_into(&mut repo, cargo_config)
-                .chain_err(|| format!("failed to fetch into {}", into.display()))?;
+                .map_err(|e| format_error(e, "fetch"))?;
             if let Ok(rev) = reference.resolve(&repo) {
                 repo_and_rev = Some((repo, rev));
             }
@@ -110,7 +143,7 @@ impl GitRemote {
             None => {
                 let repo = self
                     .clone_into(into, cargo_config)
-                    .chain_err(|| format!("failed to clone into: {}", into.display()))?;
+                    .map_err(|e| format_error(e, "clone"))?;
                 let rev = reference.resolve(&repo)?;
                 (repo, rev)
             }

tests/testsuite/git_auth.rs

@@ -265,3 +265,85 @@ Caused by:
         .run();
     t.join().ok().unwrap();
 }
+
+#[cargo_test]
+fn net_err_suggests_fetch_with_cli() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.0"
+            authors = []
+
+            [dependencies]
+            foo = { git = "ssh://needs-proxy.invalid/git" }
+        "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build -v")
+        .with_status(101)
+        .with_stderr(
+            "\
+[UPDATING] git repository `ssh://needs-proxy.invalid/git`
+warning: spurious network error[..]
+warning: spurious network error[..]
+[ERROR] failed to get `foo` as a dependency of package `foo v0.0.0 [..]`
+
+Caused by:
+  failed to load source for dependency `foo`
+
+Caused by:
+  Unable to update ssh://needs-proxy.invalid/git
+
+Caused by:
+  failed to clone into: [..]
+  If your environment requires git authentication or proxying, try enabling `git-fetch-with-cli`
+  https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli
+
+Caused by:
+  failed to resolve address for needs-proxy.invalid[..]
+",
+        )
+        .run();
+
+    p.change_file(
+        ".cargo/config",
+        "
+            [net]
+            git-fetch-with-cli = true
+            ",
+    );
+
+    p.cargo("build -v")
+        .with_status(101)
+        .with_stderr(
+            "\
+[UPDATING] git repository `ssh://needs-proxy.invalid/git`
+[RUNNING] `git fetch[..]
+[ERROR] failed to get `foo` as a dependency of package `foo v0.0.0 [..]`
+
+Caused by:
+  failed to load source for dependency `foo`
+
+Caused by:
+  Unable to update ssh://needs-proxy.invalid/git
+
+Caused by:
+  failed to fetch into: [..]
+
+Caused by:
+  [..]process didn't exit successfully[..]
+--- stderr
+ssh: Could not resolve hostname[..]
+fatal: [..]
+
+Please make sure you have the correct access rights
+and the repository exists.
+[..]",
+        )
+        .run();
+}