Fix old lockfile encoding wrt newlines

This commit fixes "old lockfile" encodings back to what they were prior
to rust-lang#7070 with respect to newlines. The changes in rust-lang#7070 accidentally
introduced a change where old lockfiles might have some extraneous
newlines removed unintentionally.

In rust-lang#7070 it was attempted to clean up how newlines are emitted to ensure
a trailing blank newline never shows up at the end of the file, but this
acccidentally regressed cases where today we actually do have blank
newlines at the end of lock files. This commit instead restores all the
previous newline handling, and then scopes the "remove trailing
newlines" fix to specifically just the new encoding.

Closes rust-lang#7254

Author: alexcrichton

src/cargo/core/mod.rs

@@ -10,7 +10,7 @@ pub use self::package::{Package, PackageSet};
 pub use self::package_id::PackageId;
 pub use self::package_id_spec::PackageIdSpec;
 pub use self::registry::Registry;
-pub use self::resolver::Resolve;
+pub use self::resolver::{Resolve, ResolveVersion};
 pub use self::shell::{Shell, Verbosity};
 pub use self::source::{GitReference, Source, SourceId, SourceMap};
 pub use self::summary::{FeatureMap, FeatureValue, Summary};

src/cargo/ops/lockfile.rs

@@ -2,7 +2,7 @@ use std::io::prelude::*;
 
 use toml;
 
-use crate::core::{resolver, Resolve, Workspace};
+use crate::core::{resolver, Resolve, ResolveVersion, Workspace};
 use crate::util::errors::{CargoResult, CargoResultExt};
 use crate::util::toml as cargo_toml;
 use crate::util::Filesystem;
@@ -122,10 +122,7 @@ fn resolve_to_string_orig(
     }
 
     let deps = toml["package"].as_array().unwrap();
-    for (i, dep) in deps.iter().enumerate() {
-        if i > 0 {
-            out.push_str("\n");
-        }
+    for dep in deps {
         let dep = dep.as_table().unwrap();
 
         out.push_str("[[package]]\n");
@@ -135,17 +132,31 @@ fn resolve_to_string_orig(
     if let Some(patch) = toml.get("patch") {
         let list = patch["unused"].as_array().unwrap();
         for entry in list {
-            out.push_str("\n[[patch.unused]]\n");
+            out.push_str("[[patch.unused]]\n");
             emit_package(entry.as_table().unwrap(), &mut out);
+            out.push_str("\n");
         }
     }
 
     if let Some(meta) = toml.get("metadata") {
-        out.push_str("\n");
         out.push_str("[metadata]\n");
         out.push_str(&meta.to_string());
     }
 
+    // Historical versions of Cargo in the old format accidentally left trailing
+    // blank newlines at the end of files, so we just leave that as-is. For all
+    // encodings going forward, though, we want to be sure that our encoded lock
+    // file doesn't contain any trailing newlines so trim out the extra if
+    // necessary.
+    match resolve.version() {
+        ResolveVersion::V1 => {}
+        _ => {
+            while out.ends_with("\n\n") {
+                out.pop();
+            }
+        }
+    }
+
     Ok((orig.ok(), out, ws_root))
 }
 
@@ -203,7 +214,8 @@ fn emit_package(dep: &toml::value::Table, out: &mut String) {
 
             out.push_str("]\n");
         }
+        out.push_str("\n");
     } else if dep.contains_key("replace") {
-        out.push_str(&format!("replace = {}\n", &dep["replace"]));
+        out.push_str(&format!("replace = {}\n\n", &dep["replace"]));
     }
 }