feat(build-analysis): build.analysis configuration

When enabled, set timing output format to HTML to pretend
we are persisting timing data for now.

src/cargo/core/compiler/build_config.rs

@@ -115,6 +115,18 @@ impl BuildConfig {
             (None, _) => false,
         };
 
+        let timing_outputs = match (cfg.analysis.as_ref(), gctx.cli_unstable().build_analysis) {
+            // Enable HTML output to pretend we are persisting timing data for now.
+            (Some(analysis), true) if analysis.enabled => vec![TimingOutput::Html],
+            (Some(_), false) => {
+                gctx.shell().warn(
+                    "ignoring 'build.analysis' config, pass `-Zbuild-analysis` to enable it",
+                )?;
+                Vec::new()
+            }
+            _ => Vec::new(),
+        };
+
         Ok(BuildConfig {
             requested_kinds,
             jobs,
@@ -130,7 +142,7 @@ impl BuildConfig {
             rustfix_diagnostic_server: Rc::new(RefCell::new(None)),
             export_dir: None,
             future_incompat_report: false,
-            timing_outputs: Vec::new(),
+            timing_outputs,
             sbom,
             compile_time_deps_only: false,
         })

src/cargo/util/context/mod.rs

@@ -2768,6 +2768,15 @@ pub struct CargoBuildConfig {
     pub warnings: Option<WarningHandling>,
     /// Unstable feature `-Zsbom`.
     pub sbom: Option<bool>,
+    /// Unstable feature `-Zbuild-analysis`.
+    pub analysis: Option<CargoBuildAnalysis>,
+}
+
+/// Metrics collection for build analysis.
+#[derive(Debug, Deserialize, Default)]
+#[serde(rename_all = "kebab-case")]
+pub struct CargoBuildAnalysis {
+    pub enabled: bool,
 }
 
 /// Whether warnings should warn, be allowed, or cause an error.

tests/testsuite/build_analysis.rs

@@ -17,6 +17,7 @@ fn gated() {
         .env("CARGO_BUILD_ANALYSIS_ENABLED", "true")
         .masquerade_as_nightly_cargo(&["build-analysis"])
         .with_stderr_data(str![[r#"
+[WARNING] ignoring 'build.analysis' config, pass `-Zbuild-analysis` to enable it
 [CHECKING] foo v0.0.0 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
@@ -36,6 +37,7 @@ fn simple() {
         .masquerade_as_nightly_cargo(&["build-analysis"])
         .with_stderr_data(str![[r#"
 [CHECKING] foo v0.0.0 ([ROOT]/foo)
+      Timing report saved to [ROOT]/foo/target/cargo-timings/cargo-timing-[..].html
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])