Cap lints at warn when cargo installing

src/bin/cargo/commands/install.rs

@@ -1,6 +1,7 @@
 use crate::command_prelude::*;
 
 use cargo::core::{GitReference, SourceId};
+use cargo::core::compiler::LintLevel;
 use cargo::ops;
 use cargo::util::ToUrl;
 
@@ -84,6 +85,9 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
 
     compile_opts.build_config.release = !args.is_present("debug");
 
+    // Cap lints at warn, so crates with deny or forbid clauses can be installed
+    compile_opts.build_config.cap_lints = Some(LintLevel::Warn);
+
     let krates = args
         .values_of("crate")
         .unwrap_or_default()

src/cargo/core/compiler/build_config.rs

@@ -29,6 +29,7 @@ pub struct BuildConfig {
     pub extra_rustc_env: Vec<(String, String)>,
     /// Extra args to inject into rustc commands.
     pub extra_rustc_args: Vec<String>,
+    pub cap_lints: Option<LintLevel>,
     pub rustfix_diagnostic_server: RefCell<Option<RustfixDiagnosticServer>>,
 }
 
@@ -91,6 +92,7 @@ impl BuildConfig {
             cargo_as_rustc_wrapper: false,
             extra_rustc_env: Vec::new(),
             extra_rustc_args: Vec::new(),
+            cap_lints: None,
             rustfix_diagnostic_server: RefCell::new(None),
         })
     }
@@ -211,3 +213,8 @@ impl CompileMode {
         &ALL
     }
 }
+
+#[derive(Debug)]
+pub enum LintLevel {
+    Allow, Warn, Deny, Forbid,
+}

src/cargo/core/compiler/mod.rs

@@ -29,7 +29,7 @@ use crate::util::errors::{CargoResult, CargoResultExt, Internal, ProcessError};
 use crate::util::paths;
 use crate::util::{self, machine_message, process, Freshness, ProcessBuilder};
 use crate::util::{internal, join_paths, profile};
-pub use self::build_config::{BuildConfig, CompileMode, MessageFormat};
+pub use self::build_config::{BuildConfig, CompileMode, LintLevel, MessageFormat};
 pub use self::build_context::{BuildContext, FileFlavor, TargetConfig, TargetInfo};
 use self::build_plan::BuildPlan;
 pub use self::compilation::{Compilation, Doctest};
@@ -717,6 +717,15 @@ fn add_cap_lints(bcx: &BuildContext<'_, '_>, unit: &Unit<'_>, cmd: &mut ProcessB
     // don't fail compilation.
     } else if !unit.pkg.package_id().source_id().is_path() {
         cmd.arg("--cap-lints").arg("warn");
+
+    // If we have a BuildConfig-wide lint cap set, use that.
+    } else if let Some(cap_lints) = &bcx.build_config.cap_lints {
+        cmd.arg("--cap-lints").arg(match cap_lints {
+            LintLevel::Allow => "allow",
+            LintLevel::Warn => "warn",
+            LintLevel::Deny => "deny",
+            LintLevel::Forbid => "forbid",
+        });
     }
 }