Suggest cargo install --git when missing registry package looks like a git* URL

src/cargo/ops/common_for_install_and_uninstall.rs

@@ -7,6 +7,8 @@ use std::rc::Rc;
 use std::task::Poll;
 
 use anyhow::{bail, format_err, Context as _};
+use gix::bstr::BStr;
+use gix::url::{parse, Scheme};
 use ops::FilterRule;
 use serde::{Deserialize, Serialize};
 
@@ -16,6 +18,7 @@ use crate::core::{Dependency, FeatureValue, Package, PackageId, QueryKind, Sourc
 use crate::ops::{self, CompileFilter, CompileOptions};
 use crate::sources::PathSource;
 use crate::util::errors::CargoResult;
+use crate::util::interning::InternedString;
 use crate::util::Config;
 use crate::util::{FileLock, Filesystem};
 
@@ -521,6 +524,40 @@ pub fn path_source(source_id: SourceId, config: &Config) -> CargoResult<PathSour
     Ok(PathSource::new(&path, source_id, config))
 }
 
+/// A holder for a user-facing string that helps them run
+/// cargo install --git with correct arguments
+enum InstallSuggestion {
+    /// Hint to append to the error message that the user can
+    /// run to install a package from a Git Repo
+    NormalisedGitUrl(String),
+    /// Failed to generate an install suggestion.
+    None,
+}
+
+/// Returns None if the Registry Dependency was not a GitUrl, otherwise
+/// return a suggestion with the https-normalised GitUrl for user
+/// to rerun cargo install with
+fn was_git_url_miscategorised_as_a_registry_dep(dep: &Dependency) -> InstallSuggestion {
+    if dep.source_id().is_registry() {
+        if let Ok(git_url) = parse(BStr::new(dep.package_name().as_bytes())) {
+            let final_git_url: Option<InternedString> = match git_url.scheme {
+                Scheme::Http | Scheme::Https => Some(dep.package_name()),
+                // cargo doesn't support cargo install git@ urls
+                _ => None,
+            };
+
+            if let Some(final_git_url) = final_git_url {
+                return InstallSuggestion::NormalisedGitUrl(format!(
+                    "To install a package from a git repository, use `--git {final_git_url}`",
+                ));
+            } else {
+                return InstallSuggestion::None;
+            }
+        }
+    }
+    return InstallSuggestion::None;
+}
+
 /// Gets a Package based on command-line requirements.
 pub fn select_dep_pkg<T>(
     source: &mut T,
@@ -578,12 +615,24 @@ where
                     source.source_id()
                 )
             } else {
-                bail!(
-                    "could not find `{}` in {} with version `{}`",
-                    dep.package_name(),
-                    source.source_id(),
-                    dep.version_req(),
-                )
+                if let InstallSuggestion::NormalisedGitUrl(suggestion) =
+                    was_git_url_miscategorised_as_a_registry_dep(&dep)
+                {
+                    bail!(
+                        "could not find `{}` in {} with version `{}`. {}",
+                        dep.package_name(),
+                        source.source_id(),
+                        dep.version_req(),
+                        suggestion,
+                    )
+                } else {
+                    bail!(
+                        "could not find `{}` in {} with version `{}`",
+                        dep.package_name(),
+                        source.source_id(),
+                        dep.version_req(),
+                    )
+                }
             }
         }
     }

tests/testsuite/install.rs

@@ -1642,6 +1642,19 @@ fn test_install_git_cannot_be_a_base_url() {
         .run();
 }
 
+#[cargo_test]
+fn test_install_from_https_git_generate_suggestion() {
+    registry::init();
+    cargo_process("install https://github.com/rust-lang/cargo")
+        .with_status(101)
+        .with_stderr(
+            "\
+[UPDATING] `[..]` index
+error: could not find `https://github.com/rust-lang/cargo` in registry `crates-io` with version `*`. To install a package from a git repository, use `--git https://github.com/rust-lang/cargo`",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn uninstall_multiple_and_specifying_bin() {
     cargo_process("uninstall foo bar --bin baz")