flowey: add explicit no_incremental flag for cargo builds by justus-camp-microsoft · Pull Request #3054 · microsoft/openvmm

justus-camp-microsoft · 2026-03-18T21:43:22Z

Flowey needs the ability to set if the build is incremental or not so that the build-reproducible pipeline can set it and not have machine-dependent paths as part of its target directory outputs. This change makes that configuration explicit rather than just plumbing in the environment variable based on CI or not.

This change is part of a few remaining changes needed to get OpenHCL building reproducibly across machines.

justus-camp-microsoft · 2026-03-18T21:43:56Z

flowey/flowey_lib_common/src/run_cargo_build.rs

-                    } else {
-                        // if build locally, use per-package target dirs
-                        // to avoid rebuilding
-                        // TODO: remove this once cargo's caching improves
-                        cmd = cmd
-                            .arg("--target-dir")
-                            .arg(in_folder.join("target").join(&crate_name));


I'm not sure if this should be removed - has cargo's caching gotten better? How would we even validate that?

Copilot

Pull request overview

Adds an explicit no_incremental configuration knob to Flowey’s common cargo-flag plumbing so pipelines (notably the local build-reproducible workflow) can opt out of incremental compilation for more reproducible outputs.

Changes:

Introduce no_incremental into shared pipeline/job params and propagate it into cfg_cargo_common_flags.
Apply no_incremental in run_cargo_build by setting CARGO_INCREMENTAL=0 when requested.
Expose a --no-incremental CLI flag for local pipeline runs and wire it through affected pipelines.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
flowey/flowey_lib_hvlite/src/_jobs/cfg_common.rs	Adds `no_incremental` to shared job params and forwards it to common cargo flags.
flowey/flowey_lib_common/src/cfg_cargo_common_flags.rs	Extends common cargo flags with `no_incremental` and adds a setter request.
flowey/flowey_lib_common/src/run_cargo_build.rs	Consumes `no_incremental` and sets `CARGO_INCREMENTAL=0` when enabled; removes prior local `--target-dir` behavior.
flowey/flowey_lib_common/src/run_cargo_clippy.rs	Updates flags destructuring to tolerate the new field.
flowey/flowey_lib_common/src/run_cargo_doc.rs	Updates flags destructuring to tolerate the new field.
flowey/flowey_hvlite/src/pipelines_shared/cfg_common_params.rs	Adds `--no-incremental` to local CLI args and sets `no_incremental=true` for cloud backends.
flowey/flowey_hvlite/src/pipelines/build_reproducible.rs	Forces local reproducible builds to use `--locked` and `--no-incremental`.
flowey/flowey_hvlite/src/pipelines/vmm_tests.rs	Plumbs `no_incremental` into common params (set to false).
flowey/flowey_hvlite/src/pipelines/restore_packages.rs	Plumbs `no_incremental` into common params (set to false).
flowey/flowey_hvlite/src/pipelines/custom_vmfirmwareigvm_dll.rs	Plumbs `no_incremental` into common params (set to false).
flowey/flowey_hvlite/src/pipelines/build_igvm.rs	Plumbs `no_incremental` into common params (set to false).

flowey/flowey_lib_common/src/run_cargo_clippy.rs

+                    let crate::cfg_cargo_common_flags::Flags {
+                        locked, verbose, ..
+                    } = flags;


flowey/flowey_lib_common/src/run_cargo_doc.rs

+                    let crate::cfg_cargo_common_flags::Flags {
+                        locked, verbose, ..
+                    } = flags;


flowey/flowey_lib_common/src/run_cargo_build.rs

                    rt.sh.change_dir(cargo_work_dir);
                    let mut cmd = flowey::shell_cmd!(rt, "{argv0} {params...}");
-                    if !matches!(rt.backend(), FlowBackend::Local) {
-                        // if running in CI, no need to waste time with incremental
-                        // build artifacts
+                    if no_incremental {
                        with_env.insert("CARGO_INCREMENTAL".to_owned(), "0".to_owned());
-                    } else {
-                        // if build locally, use per-package target dirs
-                        // to avoid rebuilding
-                        // TODO: remove this once cargo's caching improves
-                        cmd = cmd
-                            .arg("--target-dir")
-                            .arg(in_folder.join("target").join(&crate_name));
                    }


github-actions · 2026-03-19T00:44:17Z

At least one Petri test failed.

smalis-msft · 2026-03-19T15:31:29Z

flowey/flowey_lib_common/src/run_cargo_build.rs

                    rt.sh.change_dir(cargo_work_dir);
                    let mut cmd = flowey::shell_cmd!(rt, "{argv0} {params...}");
-                    if !matches!(rt.backend(), FlowBackend::Local) {
-                        // if running in CI, no need to waste time with incremental


Are we losing this CI optimization?

No the behavior is the same, just more explicitly passed in with the no_incremental flag

The only places using this optimization are CI runs and now the Nix build. This technically could have been another backend check but I think it's better to pass it in explicitly and then have higher level nodes orchestrate whether or not it should set it or not.

smalis-msft · 2026-03-19T15:33:15Z

flowey/flowey_lib_common/src/run_cargo_doc.rs


+                    let mut env = HashMap::new();
+                    if no_incremental {
+                        env.insert("CARGO_INCREMENTAL".to_owned(), "0".to_owned());


Where is this used? Also does incremental matter for doc/clippy runs?

It shouldn't matter for docs, I think I did this to make it more consistent but I think a better thing to do here is just destructure it and ignore it. I'll push a change that does that. For clippy I think this was already plumbed so I'm keeping the same behavior there.

Copilot

Pull request overview

Adds an explicit no_incremental configuration knob to Flowey’s shared cargo-flag plumbing so pipelines (notably reproducible builds) can deterministically control whether incremental compilation is disabled, instead of relying on backend/CI heuristics.

Changes:

Introduce no_incremental in the common cfg (cfg_common) and cargo flags node (cfg_cargo_common_flags) and thread it through hvlite pipeline parameter wiring.
Update cargo build and cargo clippy Flowey nodes to set CARGO_INCREMENTAL=0 only when no_incremental is requested.
Add a --no-incremental CLI flag for local runs and default no_incremental: true for cloud params.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
flowey/flowey_lib_hvlite/src/_jobs/cfg_common.rs	Plumbs `no_incremental` from common job params into the shared cargo-flags node.
flowey/flowey_lib_common/src/cfg_cargo_common_flags.rs	Extends the shared `Flags` struct and request API with `no_incremental`.
flowey/flowey_lib_common/src/run_cargo_build.rs	Uses `Flags.no_incremental` to conditionally set `CARGO_INCREMENTAL=0` during builds.
flowey/flowey_lib_common/src/run_cargo_clippy.rs	Uses `Flags.no_incremental` to conditionally set `CARGO_INCREMENTAL=0` during clippy.
flowey/flowey_lib_common/src/run_cargo_doc.rs	Adjusts destructuring for the new flag (currently ignored).
flowey/flowey_hvlite/src/pipelines_shared/cfg_common_params.rs	Adds `--no-incremental` to local CLI args; sets `no_incremental: true` for cloud defaults.
flowey/flowey_hvlite/src/pipelines/build_reproducible.rs	Sets `locked` + `no_incremental` explicitly for the local reproducible build pipeline.
flowey/flowey_hvlite/src/pipelines/build_igvm.rs	Threads `no_incremental` into cfg_common params for this pipeline path.
flowey/flowey_hvlite/src/pipelines/vmm_tests.rs	Adds `no_incremental` field when constructing cfg_common params.
flowey/flowey_hvlite/src/pipelines/restore_packages.rs	Adds `no_incremental` field when constructing cfg_common params.
flowey/flowey_hvlite/src/pipelines/custom_vmfirmwareigvm_dll.rs	Adds `no_incremental` field when constructing cfg_common params.

flowey/flowey_lib_common/src/run_cargo_doc.rs

Copilot · 2026-03-19T21:34:17Z

flowey/flowey_lib_common/src/cfg_cargo_common_flags.rs

 pub struct Flags {
    pub locked: bool,
    pub verbose: bool,
+    pub no_incremental: bool,
 }

 flowey_request! {
    pub enum Request {
        SetLocked(bool),
        SetVerbose(ReadVar<bool>),
+        SetNoIncremental(bool),
        GetFlags(WriteVar<Flags>),
    }


Flags now carries no_incremental, and run_cargo_build/run_cargo_clippy respect it, but other cargo entry points still hardcode CARGO_INCREMENTAL=0 based on backend (e.g., nextest command generation/archive). That makes the behavior inconsistent and undermines making incremental control explicit; consider switching those call sites to use Flags.no_incremental and removing the backend-based override.

This may actually be a good comment, let me grep to make sure this shouldn't be plumbed through in other places that I missed.

github-actions · 2026-03-20T18:41:37Z

At least one Petri test failed.

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justus-camp-microsoft requested a review from a team as a code owner March 18, 2026 21:43

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justus-camp-microsoft commented Mar 18, 2026

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justus-camp-microsoft force-pushed the no_incremental branch 2 times, most recently from a18fad4 to 669ccdc Compare March 18, 2026 22:33

smalis-msft reviewed Mar 19, 2026

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Copilot AI review requested due to automatic review settings March 19, 2026 21:29

justus-camp-microsoft force-pushed the no_incremental branch from 669ccdc to cbbac83 Compare March 19, 2026 21:29

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justus-camp-microsoft force-pushed the no_incremental branch from cbbac83 to bf38951 Compare March 19, 2026 21:51

flowey: add explicit no_incremental flag for cargo builds

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justus-camp-microsoft force-pushed the no_incremental branch from bf38951 to 61b83bf Compare March 20, 2026 17:27

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