From dcbb4333408e8ca4505215de7700edad728baf31 Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Fri, 22 Jul 2022 23:52:49 -0700
Subject: [PATCH 1/2] Make the `rust-version` error recommend `cargo update -p
 crate@ver --precise ...`

People encountering a dependency with a newer `rust-version` requirement
may not know about `cargo update --precise`, or may consider alternate
approaches that may be harmful (such as pinning with a `=` dependency).

Provide specific guidance in the error message.

If the user is using `cargo install`, suggest `cargo install --locked` instead.
---
 src/cargo/ops/cargo_compile.rs  | 22 +++++++++++++++++++++-
 tests/testsuite/rust_version.rs | 10 ++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/cargo/ops/cargo_compile.rs b/src/cargo/ops/cargo_compile.rs
index 5d273295ae3..2ac85cad48a 100644
--- a/src/cargo/ops/cargo_compile.rs
+++ b/src/cargo/ops/cargo_compile.rs
@@ -661,12 +661,32 @@ pub fn create_bcx<'a, 'cfg>(
                 continue;
             }
 
+            let guidance = if ws.is_ephemeral() {
+                if ws.ignore_lock() {
+                    "Try re-running cargo install with `--locked`".to_string()
+                } else {
+                    String::new()
+                }
+            } else {
+                format!(
+                    "Either upgrade to rustc {} or newer, or use\n\
+                     cargo update -p {}@{} --precise ver\n\
+                     where `ver` is the latest version of `{}` supporting rustc {}",
+                    version,
+                    unit.pkg.name(),
+                    unit.pkg.version(),
+                    unit.pkg.name(),
+                    current_version,
+                )
+            };
+
             anyhow::bail!(
                 "package `{}` cannot be built because it requires rustc {} or newer, \
-                 while the currently active rustc version is {}",
+                 while the currently active rustc version is {}\n{}",
                 unit.pkg,
                 version,
                 current_version,
+                guidance,
             );
         }
     }
diff --git a/tests/testsuite/rust_version.rs b/tests/testsuite/rust_version.rs
index 6f849141ff6..1823cdad98a 100644
--- a/tests/testsuite/rust_version.rs
+++ b/tests/testsuite/rust_version.rs
@@ -124,7 +124,10 @@ fn rust_version_too_high() {
         .with_status(101)
         .with_stderr(
             "error: package `foo v0.0.1 ([..])` cannot be built because it requires \
-             rustc 1.9876.0 or newer, while the currently active rustc version is [..]",
+             rustc 1.9876.0 or newer, while the currently active rustc version is [..]\n\
+             Either upgrade to rustc 1.9876.0 or newer, or use\n\
+             cargo update -p foo@0.0.1 --precise ver\n\
+             where `ver` is the latest version of `foo` supporting rustc [..]",
         )
         .run();
     p.cargo("build --ignore-rust-version").run();
@@ -159,7 +162,10 @@ fn rust_version_dependency_fails() {
              Downloading crates ...\n  \
              Downloaded bar v0.0.1 (registry `[..]`)\n\
              error: package `bar v0.0.1` cannot be built because it requires \
-             rustc 1.2345.0 or newer, while the currently active rustc version is [..]",
+             rustc 1.2345.0 or newer, while the currently active rustc version is [..]\n\
+             Either upgrade to rustc 1.2345.0 or newer, or use\n\
+             cargo update -p bar@0.0.1 --precise ver\n\
+             where `ver` is the latest version of `bar` supporting rustc [..]",
         )
         .run();
     p.cargo("build --ignore-rust-version").run();

From 934e79072ab40891e6e7dacadad0505f6029515c Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Tue, 2 Aug 2022 10:50:46 -0700
Subject: [PATCH 2/2] Only show advice to use `cargo update --precise` for
 non-local packages

Packages in the local workspace can't get updated this way; the user
just needs to point to a different source, or otherwise update the
package themselves.
---
 src/cargo/ops/cargo_compile.rs  | 4 +++-
 tests/testsuite/rust_version.rs | 5 +----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/cargo/ops/cargo_compile.rs b/src/cargo/ops/cargo_compile.rs
index 2ac85cad48a..ced55770ef8 100644
--- a/src/cargo/ops/cargo_compile.rs
+++ b/src/cargo/ops/cargo_compile.rs
@@ -667,7 +667,7 @@ pub fn create_bcx<'a, 'cfg>(
                 } else {
                     String::new()
                 }
-            } else {
+            } else if !unit.is_local() {
                 format!(
                     "Either upgrade to rustc {} or newer, or use\n\
                      cargo update -p {}@{} --precise ver\n\
@@ -678,6 +678,8 @@ pub fn create_bcx<'a, 'cfg>(
                     unit.pkg.name(),
                     current_version,
                 )
+            } else {
+                String::new()
             };
 
             anyhow::bail!(
diff --git a/tests/testsuite/rust_version.rs b/tests/testsuite/rust_version.rs
index 1823cdad98a..68d54190cb0 100644
--- a/tests/testsuite/rust_version.rs
+++ b/tests/testsuite/rust_version.rs
@@ -124,10 +124,7 @@ fn rust_version_too_high() {
         .with_status(101)
         .with_stderr(
             "error: package `foo v0.0.1 ([..])` cannot be built because it requires \
-             rustc 1.9876.0 or newer, while the currently active rustc version is [..]\n\
-             Either upgrade to rustc 1.9876.0 or newer, or use\n\
-             cargo update -p foo@0.0.1 --precise ver\n\
-             where `ver` is the latest version of `foo` supporting rustc [..]",
+             rustc 1.9876.0 or newer, while the currently active rustc version is [..]\n\n",
         )
         .run();
     p.cargo("build --ignore-rust-version").run();