Finished states how the time was spent from one minute, names the longest compile by its source file, and states the profile's descriptor on the fast path

Build output design revision 3, decision D4 (section 7.3). Below a minute
Finished states the profile and the total alone. The step record carries,
per compile step, its first input relative to the innermost package root
that holds it, and Finished names the longest step by it
(longest slow: src/main.cpp 1m08s) where it named the object file. The
record's header carries the profile's descriptor, which the fast path reads
alone, so a build with nothing to do states [unoptimized + debuginfo] as a
full build does. One function, profile_descriptor, spells the descriptor
for both, from the plan's manifest that compute_flags reads. The docs, the
CHANGELOG and the design state it; D3 is recorded as no change.

Author: speak-agent

.agents/docs/2026-09-30-build-output-refinement-design.md

@@ -8,11 +8,11 @@ status: landed
 - Status: landed (revision 3). Implemented in #743, released as 2026.9.30.1.
   It refines `2026-09-29-build-progress-display-design.md` (revision 2,
   landed in #742, released as 2026.9.29.5) and replaces the parts listed in
-  section 6. Decision D3 of section 16 was settled after the implementation
-  as no change: the configuration lines stay as they are, and T6 is dropped.
-  Decision D4 is open, so the part of T4 it covers (the 60 s threshold, the
-  profile descriptor on the fast path, and the source file of `longest`) is
-  not implemented; `Finished` keeps revision 2's form there.
+  section 6. Decisions D3 and D4 of section 16 were settled after the first
+  implementation: D3 as no change (the configuration lines stay as they are,
+  and T6 is dropped), and D4 as recommended (section 7.3: the 60 s threshold,
+  the profile descriptor on the fast path, and the source file of `longest`),
+  implemented in the same pull request.
 - Date: 2026-09-30
 - Origin: a report on `mcpp build` in the xlings repository with mcpp
   2026.9.29.5. It raised three questions: why the build prints warnings;
@@ -1358,8 +1358,11 @@ of silence.
   from the consumer's key, since a package reached through `[feature-deps]`
   has no entry in the consumer's `[dependencies]`. A version 1 record is read
   with both empty, and its subject then carries what version 1 wrote there,
-  until the next plan writes version 2. The profile descriptor on the fast
-  path and the source file of `longest` (section 7.3) wait for decision D4.
+  until the next plan writes version 2. Version 2 also carries the profile's
+  descriptor in the header, which the fast path reads alone, and an `S` line
+  per compile step: the step's first input, relative to the innermost package
+  root that holds it, which `Finished` names for the longest step
+  (section 7.3).
 - **Unchanged**: the log reader and its recompaction handling, the
   attribution in the generator, the action-start file, and the heartbeat.
 

CHANGELOG.md

@@ -79,6 +79,13 @@ records one lock entry per identity again.
 - **A build program has a line when it runs or fails**; a reused program has
   one under `--verbose`. The folded `build.mcpp N dependencies` line is gone.
 - **A failure names its package**: `error: build failed in <package>`.
+- **`Finished` states how the time was spent from one minute**, where it did
+  from ten seconds; below a minute it states the profile and the total alone.
+  The longest step, when it took at least a quarter of the build, is named
+  by its source file for a compile (`longest slow: src/main.cpp 1m08s`), not
+  by its object file. A build with nothing to do states the profile's
+  descriptor as a full build does (`Finished dev [unoptimized + debuginfo]
+  in 0.02s`): the step record's header carries it for the fast path.
 - **The status row is aligned with the verbs** (`    Building 612/707 · 0:35`),
   its phases are `Planning`, `Running`, `Building`, `Stopping` and `Checking`,
   and no blank row separates it from the output.

docs/09-commands-by-scenario.md

@@ -243,7 +243,7 @@ $ mcpp build
    Compiling mcpplibs.xpkg v0.0.59
    Compiling xlings v2026.9.29.1 (.)
 
-    Finished dev [unoptimized + debuginfo] in 33.63s · plan 3.06s · programs 0.64s · build 29.94s
+    Finished dev [unoptimized + debuginfo] in 1m08s · plan 16.90s · programs 0.98s · build 50.99s
 ```
 
 - A package's line is written when the first of its steps finishes (a
@@ -264,9 +264,11 @@ $ mcpp build
 - A failed step is reported when it fails: `error: build failed in
   <package>`, then its diagnostics, while ninja waits for the steps still
   running.
-- `Finished` states the whole command's time. A command of ten seconds or
-  more also states how the time was spent, and names the step that took at
-  least a quarter of the build when there is one.
+- `Finished` states the profile and the whole command's time, whether the
+  build had work to do or not. A command of a minute or more also states how
+  the time was spent, and names the step that took at least a quarter of the
+  build when there is one: a compile by its source file, relative to its
+  package, and an action by its label.
 
 On a terminal one status row is drawn below the output and updated in place:
 

docs/zh/09-commands-by-scenario.md

@@ -224,7 +224,7 @@ $ mcpp build
    Compiling mcpplibs.xpkg v0.0.59
    Compiling xlings v2026.9.29.1 (.)
 
-    Finished dev [unoptimized + debuginfo] in 33.63s · plan 3.06s · programs 0.64s · build 29.94s
+    Finished dev [unoptimized + debuginfo] in 1m08s · plan 16.90s · programs 0.98s · build 50.99s
 ```
 
 - **何时写出**：包的第一个步骤完成时（依赖扫描不计），或它的第一个 `check`、`prepare` 动作开始时，写出该包的行；此后这一行不再改变。
@@ -238,7 +238,7 @@ $ mcpp build
 - **来源配色**：在终端上，名字的颜色表示来源。官方索引为青色，其他索引为品红，git 仓库为蓝色，项目自身的包为默认色。
 - **构建程序**：构建程序在运行或失败时有一行，并给出耗时。结果被复用的构建程序只在 `--verbose` 下有行。
 - **失败**：失败的步骤在失败时即报告：先写 `error: build failed in <包>`，再写它的诊断信息；与此同时 ninja 等待仍在运行的步骤。
-- **Finished**：`Finished` 给出整个命令的耗时。命令耗时达到十秒时，还说明时间的构成；若某一步骤占构建时间的四分之一以上，则给出该步骤。
+- **Finished**：`Finished` 给出配置档和整个命令的耗时，构建有无事可做都一样。命令耗时达到一分钟时，还说明时间的构成；若某一步骤占构建时间的四分之一以上，则给出该步骤：编译步骤给出其源文件（相对于所在包），动作给出其标签。
 
 在终端上，输出下方画一行状态行，并原地更新：
 

src/build/execute.cppm

@@ -30,7 +30,7 @@ import mcpp.freestanding.linkline;
 import mcpp.build.graph_shape;    // #407: which mode wrote this build.ninja
 import mcpp.build.backend;
 import mcpp.build.ninja;
-import mcpp.build.flags;       // realises_optimization — one answer for the level (#694)
+import mcpp.build.flags;       // profile_descriptor — one answer for the level (#694)
 import mcpp.build.runtime_validation;
 import mcpp.bmi_cache;
 import mcpp.bmi_cache.maintenance;  // dir_size + human_bytes, for `clean --stale`
@@ -1066,16 +1066,12 @@ export int run_build_plan(BuildContext& ctx, bool verbose, bool no_cache,
     if (!mcpp::diag::flush(ctx.strict)) return 1;
 
     // The descriptor reads the level the compile realised, from the one
-    // function `compute_flags` spells it from (#694). It once read the declared
-    // level while the compile used another, and said `[optimized]` over `-Og`.
-    {
-        const auto& bc = ctx.manifest.buildConfig;
-        std::string descriptor =
-            mcpp::build::realises_optimization(bc) ? "optimized" : "unoptimized";
-        if (bc.debug) descriptor += " + debuginfo";
-        if (bc.lto)   descriptor += " + lto";
-        mcpp::build::progress::finished(ctx.profile, descriptor);
-    }
+    // function `compute_flags` spells it from (#694), and from the plan's
+    // manifest, which `compute_flags` reads. It once read the declared level
+    // while the compile used another, and said `[optimized]` over `-Og`. The
+    // step record's header carries the same value for the fast path.
+    mcpp::build::progress::finished(
+        ctx.profile, mcpp::build::profile_descriptor(ctx.plan.manifest.buildConfig));
     report_freestanding_size(ctx);
     return 0;
 }
@@ -1689,7 +1685,10 @@ export std::optional<int> try_fast_build(const std::filesystem::path& projectRoo
             *validatedBefore))
         return fast_path_declined("build", "ninja relinked an artifact, whose closure the full path validates"); // relinked: full path reconstructs + validates closure
 
-    mcpp::build::progress::finished(want->profile, "");
+    // The descriptor the plan recorded (revision 3, §7.3); empty for a record
+    // written before it was carried.
+    mcpp::build::progress::finished(want->profile,
+                                    mcpp::build::progress::read_descriptor(outputDir));
     return 0;
 }
 
@@ -1799,7 +1798,10 @@ export std::optional<int> try_fast_workspace_build(
         if (!mcpp::build::runtime_validation::artifact_snapshot_unchanged(r.validated))
             return fast_path_declined("workspace", "ninja relinked an artifact, whose closure the full path validates");
     }
-    mcpp::build::progress::finished(profile, "");
+    // The groups share the profile, and so its descriptor.
+    mcpp::build::progress::finished(
+        profile, ready.empty() ? std::string{}
+                               : mcpp::build::progress::read_descriptor(ready.front().outputDir));
     return 0;
 }
 

src/build/flags.cppm

@@ -203,6 +203,13 @@ std::string realised_opt_level(const mcpp::manifest::BuildConfig& bc);
 // Whether `realised_opt_level` names an optimizing level.
 bool realises_optimization(const mcpp::manifest::BuildConfig& bc);
 
+// The profile as `Finished` describes it: `optimized` or `unoptimized` by the
+// realised level, then `+ debuginfo` and `+ lto` when they are on. The full
+// path states it from the plan it built, and the step record's header carries
+// it for the fast path, which has no plan (build output design revision 3,
+// §7.3): both read this one function.
+std::string profile_descriptor(const mcpp::manifest::BuildConfig& bc);
+
 // The sysroot of an ELF link over a graph-supplied C library: an empty
 // directory inside the build directory, so the driver derives no library
 // search from the host (#696). `compute_flags` names it and the backend creates
@@ -606,6 +613,13 @@ bool realises_optimization(const mcpp::manifest::BuildConfig& bc) {
     return realised_opt_level(bc) != "0";
 }
 
+std::string profile_descriptor(const mcpp::manifest::BuildConfig& bc) {
+    std::string d = realises_optimization(bc) ? "optimized" : "unoptimized";
+    if (bc.debug) d += " + debuginfo";
+    if (bc.lto)   d += " + lto";
+    return d;
+}
+
 std::filesystem::path graph_link_sysroot(const std::filesystem::path& outputDir) {
     return outputDir / kGraphLinkSysrootDir;
 }

src/build/ninja_backend.cppm

@@ -1226,7 +1226,12 @@ mcpp::build::progress::Record step_record(const BuildPlan& plan,
     declared.reserve(plan.packages.size());
     for (auto const& p : plan.packages)
         declared.push_back({p.name, p.requested, p.subject, p.cachedUnits, 0, p.detail, p.source});
-    return attribution.record(declared);
+    // A compile's source is stated relative to its package's root, and the
+    // profile's descriptor is the one `Finished` states on the full path, so
+    // that the fast path states it too (build output design revision 3, §7.3).
+    auto record = attribution.record(declared, plan.packageRoots);
+    record.descriptor = profile_descriptor(plan.manifest.buildConfig);
+    return record;
 }
 
 // The aggregate target for everything staged out of the global cache. Named