Update to most recent viable nightly

Previously, if the user had components installed on `nightly` which were
not available for the latest nightly, `rustup update` would not update
the user's nightly at all. With this patch, rustup will try
progressively older nightlies until it finds a nightly that supports all
the components the user has installed for their current nightly.

Fixes rust-lang#1628.
Makes progress towards rust-lang#1501.
Fixes the underlying issue in rust-lang#1676.

Cargo.toml

@@ -22,6 +22,7 @@ no-self-update = []
 
 # Sorted by alphabetic order
 [dependencies]
+chrono = "0.4"
 clap = "2"
 download = { path = "download" }
 error-chain = "0.12"

src/dist/dist.rs

@@ -7,6 +7,7 @@ use crate::dist::temp;
 use crate::errors::*;
 use crate::utils::utils;
 
+use chrono::prelude::*;
 use lazy_static::lazy_static;
 use regex::Regex;
 
@@ -599,6 +600,81 @@ fn update_from_dist_<'a>(
     profile: Option<Profile>,
     prefix: &InstallPrefix,
     force_update: bool,
+) -> Result<Option<String>> {
+    let mut toolchain = toolchain.clone();
+    let mut fetched = String::new();
+    let backtrack = toolchain.channel == "nightly" && toolchain.date.is_none();
+    loop {
+        match try_update_from_dist_(
+            download,
+            update_hash,
+            &toolchain,
+            profile,
+            prefix,
+            force_update,
+            &mut fetched,
+        ) {
+            Ok(v) => break Ok(v),
+            Err(e) => {
+                if !backtrack {
+                    break Err(e);
+                }
+
+                let components =
+                    if let ErrorKind::RequestedComponentsUnavailable(components, ..) = e.kind() {
+                        components
+                    } else {
+                        break Err(e);
+                    };
+
+                (download.notify_handler)(Notification::SkippingNightlyMissingComponent(
+                    components,
+                ));
+
+                // The user asked to update their nightly, but the latest nightly does not have all
+                // the components that the user currently has installed. Let's try the previous
+                // nightly (recursively) until we find a nightly that does.
+                //
+                // NOTE: we don't need to explicitly check for the case where the next nightly to
+                // try is _older_ than the current nightly, since we know that the user's current
+                // nightlys supports the components they have installed, and thus would always
+                // terminate the search.
+                if let Some(ref mut date) = toolchain.date {
+                    // recurse
+                    toolchain.date = Some(
+                        Utc.from_utc_date(
+                            &NaiveDate::parse_from_str(date, "%Y-%m-%d")
+                                .expect("we constructed this date string below"),
+                        )
+                        .pred()
+                        .format("%Y-%m-%d")
+                        .to_string(),
+                    );
+                } else {
+                    // Pick a nightly that is one day older than the latest.
+                    toolchain.date = Some(
+                        Utc.from_utc_date(
+                            &NaiveDate::parse_from_str(&fetched, "%Y-%m-%d")
+                                .expect("manifest carries invalid date"),
+                        )
+                        .pred()
+                        .format("%Y-%m-%d")
+                        .to_string(),
+                    );
+                }
+            }
+        }
+    }
+}
+
+fn try_update_from_dist_<'a>(
+    download: DownloadCfg<'a>,
+    update_hash: Option<&Path>,
+    toolchain: &ToolchainDesc,
+    profile: Option<Profile>,
+    prefix: &InstallPrefix,
+    force_update: bool,
+    fetched: &mut String,
 ) -> Result<Option<String>> {
     let toolchain_str = toolchain.to_string();
     let manifestation = Manifestation::open(prefix.clone(), toolchain.target.clone())?;
@@ -622,6 +698,8 @@ fn update_from_dist_<'a>(
                 remove_components: Vec::new(),
             };
 
+            *fetched = m.date.clone();
+
             return match manifestation.update(
                 &m,
                 changes,

src/dist/notifications.rs

@@ -1,4 +1,5 @@
 use crate::dist::dist::TargetTriple;
+use crate::dist::manifest::Component;
 use crate::dist::temp;
 use crate::errors::*;
 use crate::utils::notify::NotificationLevel;
@@ -29,6 +30,7 @@ pub enum Notification<'a> {
     DownloadingManifest(&'a str),
     DownloadedManifest(&'a str, Option<&'a str>),
     DownloadingLegacyManifest,
+    SkippingNightlyMissingComponent(&'a [Component]),
     ManifestChecksumFailedHack,
     ComponentUnavailable(&'a str, Option<&'a TargetTriple>),
     StrayHash(&'a Path),
@@ -66,6 +68,7 @@ impl<'a> Notification<'a> {
             | ManifestChecksumFailedHack
             | RollingBack
             | DownloadingManifest(_)
+            | SkippingNightlyMissingComponent(_)
             | DownloadedManifest(_, _) => NotificationLevel::Info,
             CantReadUpdateHash(_)
             | ExtensionNotInstalled(_)
@@ -158,6 +161,11 @@ impl<'a> Display for Notification<'a> {
                 "removing stray hash found at '{}' in order to continue",
                 path.display()
             ),
+            SkippingNightlyMissingComponent(components) => write!(
+                f,
+                "skipping nightly which is missing installed component '{}'",
+                components[0].short_name_in_manifest()
+            ),
         }
     }
 }

tests/cli-misc.rs

@@ -756,6 +756,27 @@ fn update_unavailable_rustc() {
     });
 }
 
+#[test]
+fn update_nightly_even_with_incompat() {
+    clitools::setup(Scenario::MissingComponent, &|config| {
+        set_current_dist_date(config, "2019-09-12");
+        expect_ok(config, &["rustup", "default", "nightly"]);
+
+        expect_stdout_ok(config, &["rustc", "--version"], "hash-n-1");
+        expect_ok(config, &["rustup", "component", "add", "rls"]);
+        expect_component_executable(config, "rls");
+
+        // latest nightly is now one that does not have RLS
+        set_current_dist_date(config, "2019-09-14");
+
+        expect_component_executable(config, "rls");
+        // update should bring us to latest nightly that does
+        expect_ok(config, &["rustup", "update", "nightly", "--no-self-update"]);
+        expect_stdout_ok(config, &["rustc", "--version"], "hash-n-2");
+        expect_component_executable(config, "rls");
+    });
+}
+
 #[test]
 fn completion_rustup() {
     setup(&|config| {