Improve error message when git is not installed

When installing git dependencies without git installed, show a clear
error message directly where the error occurs.

Before:
  error: FileNotFound cloning repository for git+https://...

After:
  error: Git is not installed. Install Git to clone repository for "package"

    Learn more: https://git-scm.com/downloads

The fix checks for FileNotFound errors in repository.zig at each git
command invocation (fetch, clone, checkout, log) and logs the helpful
message right there, rather than propagating a custom error type.

src/install/PackageManager/runTasks.zig

@@ -724,16 +724,26 @@ pub fn runTasks(
                             url,
                         );
                     } else if (log_level != .silent) {
-                        manager.log.addErrorFmt(
-                            null,
-                            logger.Loc.Empty,
-                            manager.allocator,
-                            "{s} cloning repository for <b>{s}<r>",
-                            .{
-                                @errorName(err),
-                                name,
-                            },
-                        ) catch |e| bun.handleOom(e);
+                        if (err == error.GitNotFound) {
+                            manager.log.addErrorFmt(
+                                null,
+                                logger.Loc.Empty,
+                                manager.allocator,
+                                "Git is not installed. Install Git to clone repository for <b>{s}<r>\n\n  Learn more: https://git-scm.com/downloads",
+                                .{name},
+                            ) catch |e| bun.handleOom(e);
+                        } else {
+                            manager.log.addErrorFmt(
+                                null,
+                                logger.Loc.Empty,
+                                manager.allocator,
+                                "{s} cloning repository for <b>{s}<r>",
+                                .{
+                                    @errorName(err),
+                                    name,
+                                },
+                            ) catch |e| bun.handleOom(e);
+                        }
                     }
                     continue;
                 }
@@ -798,16 +808,26 @@ pub fn runTasks(
                 if (task.status == .fail) {
                     const err = task.err orelse error.Failed;
 
-                    manager.log.addErrorFmt(
-                        null,
-                        logger.Loc.Empty,
-                        manager.allocator,
-                        "{s} checking out repository for <b>{s}<r>",
-                        .{
-                            @errorName(err),
-                            alias.slice(),
-                        },
-                    ) catch |e| bun.handleOom(e);
+                    if (err == error.GitNotFound) {
+                        manager.log.addErrorFmt(
+                            null,
+                            logger.Loc.Empty,
+                            manager.allocator,
+                            "Git is not installed. Install Git to checkout repository for <b>{s}<r>\n\n  Learn more: https://git-scm.com/downloads",
+                            .{alias.slice()},
+                        ) catch |e| bun.handleOom(e);
+                    } else {
+                        manager.log.addErrorFmt(
+                            null,
+                            logger.Loc.Empty,
+                            manager.allocator,
+                            "{s} checking out repository for <b>{s}<r>",
+                            .{
+                                @errorName(err),
+                                alias.slice(),
+                            },
+                        ) catch |e| bun.handleOom(e);
+                    }
 
                     continue;
                 }

src/install/repository.zig

@@ -498,13 +498,23 @@ pub const Repository = extern struct {
                 env,
                 &[_]string{ "git", "-C", path, "fetch", "--quiet" },
             ) catch |err| {
-                log.addErrorFmt(
-                    null,
-                    logger.Loc.Empty,
-                    allocator,
-                    "\"git fetch\" for \"{s}\" failed",
-                    .{name},
-                ) catch unreachable;
+                if (err == error.FileNotFound) {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "Git is not installed. Install Git to clone repository for \"{s}\"\n\n  Learn more: https://git-scm.com/downloads",
+                        .{name},
+                    ) catch unreachable;
+                } else {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "\"git fetch\" for \"{s}\" failed",
+                        .{name},
+                    ) catch unreachable;
+                }
                 return err;
             };
             break :fetch dir;
@@ -522,7 +532,15 @@ pub const Repository = extern struct {
                 url,
                 target,
             }) catch |err| {
-                if (err == error.RepositoryNotFound or attempt > 1) {
+                if (err == error.FileNotFound) {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "Git is not installed. Install Git to clone repository for \"{s}\"\n\n  Learn more: https://git-scm.com/downloads",
+                        .{name},
+                    ) catch unreachable;
+                } else if (err == error.RepositoryNotFound or attempt > 1) {
                     log.addErrorFmt(
                         null,
                         logger.Loc.Empty,
@@ -561,13 +579,23 @@ pub const Repository = extern struct {
             else
                 &[_]string{ "git", "-C", path, "log", "--format=%H", "-1" },
         ) catch |err| {
-            log.addErrorFmt(
-                null,
-                logger.Loc.Empty,
-                allocator,
-                "no commit matching \"{s}\" found for \"{s}\" (but repository exists)",
-                .{ committish, name },
-            ) catch unreachable;
+            if (err == error.FileNotFound) {
+                log.addErrorFmt(
+                    null,
+                    logger.Loc.Empty,
+                    allocator,
+                    "Git is not installed. Install Git to use git dependencies\n\n  Learn more: https://git-scm.com/downloads",
+                    .{},
+                ) catch unreachable;
+            } else {
+                log.addErrorFmt(
+                    null,
+                    logger.Loc.Empty,
+                    allocator,
+                    "no commit matching \"{s}\" found for \"{s}\" (but repository exists)",
+                    .{ committish, name },
+                ) catch unreachable;
+            }
             return err;
         }, " \t\r\n");
     }
@@ -599,26 +627,46 @@ pub const Repository = extern struct {
                 try bun.getFdPath(.fromStdDir(repo_dir), &final_path_buf),
                 target,
             }) catch |err| {
-                log.addErrorFmt(
-                    null,
-                    logger.Loc.Empty,
-                    allocator,
-                    "\"git clone\" for \"{s}\" failed",
-                    .{name},
-                ) catch unreachable;
+                if (err == error.FileNotFound) {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "Git is not installed. Install Git to use git dependencies\n\n  Learn more: https://git-scm.com/downloads",
+                        .{},
+                    ) catch unreachable;
+                } else {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "\"git clone\" for \"{s}\" failed",
+                        .{name},
+                    ) catch unreachable;
+                }
                 return err;
             };
 
             const folder = Path.joinAbsString(PackageManager.get().cache_directory_path, &.{folder_name}, .auto);
 
             _ = exec(allocator, env, &[_]string{ "git", "-C", folder, "checkout", "--quiet", resolved }) catch |err| {
-                log.addErrorFmt(
-                    null,
-                    logger.Loc.Empty,
-                    allocator,
-                    "\"git checkout\" for \"{s}\" failed",
-                    .{name},
-                ) catch unreachable;
+                if (err == error.FileNotFound) {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "Git is not installed. Install Git to use git dependencies\n\n  Learn more: https://git-scm.com/downloads",
+                        .{},
+                    ) catch unreachable;
+                } else {
+                    log.addErrorFmt(
+                        null,
+                        logger.Loc.Empty,
+                        allocator,
+                        "\"git checkout\" for \"{s}\" failed",
+                        .{name},
+                    ) catch unreachable;
+                }
                 return err;
             };
             var dir = try bun.openDir(cache_dir, folder_name);