feat(task): add affected JSON output

TASK_CACHE_PARITY.md

@@ -73,7 +73,7 @@ outside this tracker.
 - [x] Allow affected selection to feed existing task patterns, dependency expansion, scheduling, and
       caching
 - [x] Show why each project and task was considered affected
-- [ ] Add machine-readable affected-project and affected-task output
+- [x] Add machine-readable affected-project and affected-task output
 
 ## Local cache parity
 

docs/cli/run.md

@@ -55,6 +55,10 @@ Explain why projects and tasks were selected by --affected
 Git head revision for --affected
 Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 
+### `--affected-json`
+
+Output affected projects and tasks as JSON without running tasks
+
 ### `-c --continue-on-error`
 
 Continue running tasks even if one fails

docs/cli/tasks/run.md

@@ -69,6 +69,10 @@ Explain why projects and tasks were selected by --affected
 Git head revision for --affected
 Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 
+### `--affected-json`
+
+Output affected projects and tasks as JSON without running tasks
+
 ### `-c --continue-on-error`
 
 Continue running tasks even if one fails

docs/tasks/monorepo.md

@@ -374,6 +374,9 @@ mise run --affected build
 # Inspect the selection while preserving normal dry-run behavior
 mise run --affected --affected-explain --dry-run build
 
+# Emit the selection as JSON without running tasks
+mise run --affected --affected-json build
+
 # Compare explicit revisions
 mise run --affected --affected-base origin/main --affected-head HEAD test
 ```
@@ -384,6 +387,10 @@ It also lists the task-pattern matches associated with those projects. Normal ta
 expanded afterward, so a selected task can still run a required prerequisite from an unchanged
 project.
 
+`--affected-json` emits the same pre-expansion selection without running tasks. Its stable JSON
+object contains the base and head revisions, affected projects with their roots and reasons, and
+task-pattern matches with their associated project IDs.
+
 The revision defaults are `HEAD~1` and `HEAD` locally. `MISE_AFFECTED_BASE` and
 `MISE_AFFECTED_HEAD` override them. GitHub Actions and GitLab merge-request metadata provide CI
 defaults when those variables are not set; explicit CLI options take highest precedence.

e2e/tasks/test_task_affected

@@ -68,6 +68,43 @@ git commit -qm initial
 echo changed >>crates/core/src/lib.rs
 git add .
 git commit -qm core-change
+assert_json "mise run --affected --affected-json build" '{
+  "base": "HEAD~1",
+  "head": "HEAD",
+  "projects": [
+    {
+      "id": "cargo:app",
+      "root": "crates/app",
+      "reasons": [
+        {
+          "type": "dependent",
+          "dependency": "cargo:core"
+        }
+      ]
+    },
+    {
+      "id": "cargo:core",
+      "root": "crates/core",
+      "reasons": [
+        {
+          "type": "changed-path",
+          "path": "crates/core/src/lib.rs"
+        }
+      ]
+    }
+  ],
+  "tasks": [
+    {
+      "name": "//crates/app:build",
+      "projects": ["cargo:app"]
+    },
+    {
+      "name": "//crates/core:build",
+      "projects": ["cargo:core"]
+    }
+  ]
+}'
+assert "test ! -e affected.log"
 output=$(mise run --affected --affected-explain --jobs 1 build)
 assert_contains "echo \"$output\"" "Affected projects (HEAD~1...HEAD):"
 assert_contains "echo \"$output\"" "changed path: crates/core/src/lib.rs"

man/man1/mise.1

@@ -3039,6 +3039,9 @@ Explain why projects and tasks were selected by \-\-affected
 Git head revision for \-\-affected
 Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 .TP
+\fB\-\-affected\-json\fR
+Output affected projects and tasks as JSON without running tasks
+.TP
 \fB\-c, \-\-continue\-on\-error\fR
 Continue running tasks even if one fails
 .TP
@@ -3848,6 +3851,9 @@ Explain why projects and tasks were selected by \-\-affected
 Git head revision for \-\-affected
 Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 .TP
+\fB\-\-affected\-json\fR
+Output affected projects and tasks as JSON without running tasks
+.TP
 \fB\-c, \-\-continue\-on\-error\fR
 Continue running tasks even if one fails
 .TP

mise.usage.kdl

@@ -3059,6 +3059,7 @@ Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 """# {
         arg <REV>
     }
+    flag --affected-json help="Output affected projects and tasks as JSON without running tasks"
     flag "-c --continue-on-error" help="Continue running tasks even if one fails"
     flag "-C --cd" help="Change to this directory before executing the command" {
         arg <CD>
@@ -3908,6 +3909,7 @@ Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
 """# {
             arg <REV>
         }
+        flag --affected-json help="Output affected projects and tasks as JSON without running tasks"
         flag "-c --continue-on-error" help="Continue running tasks even if one fails"
         flag "-C --cd" help="Change to this directory before executing the command" {
             arg <CD>

src/cli/bootstrap.rs

@@ -903,6 +903,7 @@ impl Bootstrap {
             affected_base: None,
             affected_head: None,
             affected_explain: false,
+            affected_json: false,
             cd: None,
             continue_on_error: false,
             dry_run: self.dry_run,

src/cli/mod.rs

@@ -779,6 +779,7 @@ impl Cli {
                         affected_base: None,
                         affected_head: None,
                         affected_explain: false,
+                        affected_json: false,
                         cd: self.cd,
                         continue_on_error: self.continue_on_error,
                         dry_run: self.dry_run,

src/cli/run.rs

@@ -25,6 +25,7 @@ use clap::{CommandFactory, ValueHint};
 use eyre::{Result, bail, eyre};
 use futures_util::FutureExt;
 use itertools::Itertools;
+use serde::Serialize;
 use std::panic::AssertUnwindSafe;
 use tokio::sync::Mutex;
 
@@ -84,14 +85,28 @@ pub struct Run {
     pub affected_base: Option<String>,
 
     /// Explain why projects and tasks were selected by --affected
-    #[clap(long, requires = "affected", verbatim_doc_comment)]
+    #[clap(
+        long,
+        requires = "affected",
+        conflicts_with = "affected_json",
+        verbatim_doc_comment
+    )]
     pub affected_explain: bool,
 
     /// Git head revision for --affected
     /// Defaults to MISE_AFFECTED_HEAD, CI metadata, or HEAD
     #[clap(long, requires = "affected", value_name = "REV", verbatim_doc_comment)]
     pub affected_head: Option<String>,
 
+    /// Output affected projects and tasks as JSON without running tasks
+    #[clap(
+        long,
+        requires = "affected",
+        conflicts_with = "affected_explain",
+        verbatim_doc_comment
+    )]
+    pub affected_json: bool,
+
     /// Continue running tasks even if one fails
     #[clap(long, short = 'c', verbatim_doc_comment)]
     pub continue_on_error: bool,
@@ -293,6 +308,7 @@ async fn get_affected_task_list(
     base: Option<&str>,
     head: Option<&str>,
     explain: bool,
+    json: bool,
 ) -> Result<Vec<Task>> {
     Settings::get().ensure_experimental("affected tasks")?;
     let workspace_root = config
@@ -365,12 +381,84 @@ async fn get_affected_task_list(
                 .map(crate::file::desymlink_path)
                 .is_some_and(|root| affected_roots.contains(&root))
     });
-    if explain {
+    if json {
+        display_affected_json(&revisions, &workspace_root, &graph, &affected, &tasks)?;
+    } else if explain {
         display_affected_explanation(&revisions, &workspace_root, &graph, &affected, &tasks)?;
     }
     Ok(tasks)
 }
 
+#[derive(Serialize)]
+struct AffectedSelectionOutput<'a> {
+    base: &'a str,
+    head: &'a str,
+    projects: Vec<AffectedProjectOutput<'a>>,
+    tasks: Vec<AffectedTaskOutput<'a>>,
+}
+
+#[derive(Serialize)]
+struct AffectedProjectOutput<'a> {
+    id: &'a crate::task::workspace::ProjectId,
+    root: &'a std::path::Path,
+    reasons: &'a BTreeSet<crate::task::workspace::AffectedProjectReason>,
+}
+
+#[derive(Serialize)]
+struct AffectedTaskOutput<'a> {
+    name: &'a str,
+    projects: Vec<&'a crate::task::workspace::ProjectId>,
+}
+
+fn display_affected_json(
+    revisions: &crate::task::workspace::git::WorkspaceGitRevisions,
+    workspace_root: &std::path::Path,
+    graph: &crate::task::workspace::WorkspaceProjectGraph,
+    affected: &crate::task::workspace::AffectedProjects,
+    tasks: &[Task],
+) -> Result<()> {
+    let mut projects_by_root = BTreeMap::<PathBuf, Vec<_>>::new();
+    let projects = affected
+        .projects()
+        .map(|(id, reasons)| {
+            let project = graph.get(id).expect("affected project exists in graph");
+            projects_by_root
+                .entry(crate::file::desymlink_path(
+                    &workspace_root.join(&project.root),
+                ))
+                .or_default()
+                .push(id);
+            AffectedProjectOutput {
+                id,
+                root: &project.root,
+                reasons,
+            }
+        })
+        .collect();
+    let mut tasks = tasks
+        .iter()
+        .map(|task| AffectedTaskOutput {
+            name: &task.display_name,
+            projects: task
+                .config_root
+                .as_deref()
+                .map(crate::file::desymlink_path)
+                .and_then(|root| projects_by_root.get(&root))
+                .cloned()
+                .unwrap_or_default(),
+        })
+        .collect::<Vec<_>>();
+    tasks.sort_by(|left, right| left.name.cmp(right.name));
+    let output = AffectedSelectionOutput {
+        base: &revisions.base,
+        head: &revisions.head,
+        projects,
+        tasks,
+    };
+    miseprintln!("{}", serde_json::to_string_pretty(&output)?);
+    Ok(())
+}
+
 fn display_affected_explanation(
     revisions: &crate::task::workspace::git::WorkspaceGitRevisions,
     workspace_root: &std::path::Path,
@@ -532,11 +620,15 @@ impl Run {
                 self.affected_base.as_deref(),
                 self.affected_head.as_deref(),
                 self.affected_explain,
+                self.affected_json,
             )
             .await?
         } else {
             get_task_lists(&config, &args, true, self.skip_deps).await?
         };
+        if self.affected_json {
+            return Ok(());
+        }
 
         // Args after -- go directly to tasks (no prefix). They are also
         // recorded on `trailing_args` so the task renderer can detect