From acc3657fb7df2866982eed9cbe1a28493cf5844e Mon Sep 17 00:00:00 2001
From: Norbert Hartl <norbert@hartl.name>
Date: Thu, 17 Sep 2026 22:06:15 +0200
Subject: [PATCH] Let a leaf read from a block

Every runtime value the servers export has no pragma to declare it - the five
of #apptiveGrid, the two of the worker, the 23 of #soil. They all need a leaf
whose value is worked out on the spot, and the tree could already hold one:
the block is the object and evaluating it is the read.

Spelling that out at the call site works but reads like a trick, and there
are some thirty of them to write. CanopyAccessor reading: [ ... ] says what
it is instead.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 .../CanopyAccessorTest.class.st               | 12 ++++++++++
 source/Canopy-Core/CanopyAccessor.class.st    | 11 +++++++++
 .../CanopyMetricsVisitorTest.class.st         | 24 +++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/source/Canopy-Core-Tests/CanopyAccessorTest.class.st b/source/Canopy-Core-Tests/CanopyAccessorTest.class.st
index eba3b93..21b06b4 100644
--- a/source/Canopy-Core-Tests/CanopyAccessorTest.class.st
+++ b/source/Canopy-Core-Tests/CanopyAccessorTest.class.st
@@ -5,6 +5,18 @@ Class {
 	#package : 'Canopy-Core-Tests'
 }
 
+{ #category : 'as yet unclassified' }
+CanopyAccessorTest >> testALeafCanReadFromABlockInsteadOfAComponent [
+	"Runtime values have no pragma to declare them - the block is the object and evaluating it is
+	the read. The value stays live, which is the whole point: it is worked out per scrape."
+	| count leaf |
+	count := 0.
+	leaf := CanopyAccessor reading: [ count ].
+	self assert: leaf value equals: 0.
+	count := 42.
+	self assert: leaf value equals: 42
+]
+
 { #category : 'as yet unclassified' }
 CanopyAccessorTest >> testAcceptCanopySkipsWriteOnlyAccessorsInsteadOfCrashing [
 	"Found 2026-07-21 while sanity-checking format: over the real Canopy systemMetrics
diff --git a/source/Canopy-Core/CanopyAccessor.class.st b/source/Canopy-Core/CanopyAccessor.class.st
index 4a921ae..806026c 100644
--- a/source/Canopy-Core/CanopyAccessor.class.st
+++ b/source/Canopy-Core/CanopyAccessor.class.st
@@ -10,6 +10,17 @@ Class {
 	#package : 'Canopy-Core'
 }
 
+{ #category : 'instance creation' }
+CanopyAccessor class >> reading: aBlock [
+	"A leaf whose value is worked out on the spot instead of being read off a component: the
+	block is the object and evaluating it is the read. That is how a value nobody declared with
+	a pragma gets into the tree - every runtime metric of the servers is built that way."
+	^ self new
+		object: aBlock;
+		readSelector: #value;
+		yourself
+]
+
 { #category : 'visiting' }
 CanopyAccessor >> acceptCanopy: aVisitor [
 	"Write-only accessors (no readSelector) contribute nothing to export/formatting -
diff --git a/source/Canopy-Metrics-Tests/CanopyMetricsVisitorTest.class.st b/source/Canopy-Metrics-Tests/CanopyMetricsVisitorTest.class.st
index 8e5a744..2704a1e 100644
--- a/source/Canopy-Metrics-Tests/CanopyMetricsVisitorTest.class.st
+++ b/source/Canopy-Metrics-Tests/CanopyMetricsVisitorTest.class.st
@@ -141,6 +141,30 @@ CanopyMetricsVisitorTest >> testAFamilyIsWrittenAsHelpTypeAndOneLine [
 	self assert: (lines third substrings last allSatisfy: [ :each | each isDigit ])
 ]
 
+{ #category : 'as yet unclassified' }
+CanopyMetricsVisitorTest >> testABlockBackedMetricExportsLikeAnyOther [
+	"The shape every runtime metric of the servers will take: no pragma anywhere, the block hands
+	back a full holder, and the exported line is indistinguishable from a declared one - inherited
+	label included. All of #apptiveGrid and the 23 #soil values are built like this today."
+	| count root soil |
+	count := 41.
+	root := CanopyBranchNode new.
+	soil := CanopyBranchNode new.
+	root at: #soil put: soil.
+	root labelAt: #stage put: 'production'.
+	soil
+		at: #objectsSerialized
+		put: (CanopyAccessor reading: [ CanopyMetric new
+			type: #counter;
+			description: 'the number of serialized objects';
+			value: count ]).
+	self assert: ((CanopyPrometheusVisitor new format: root) lines last
+		beginsWith: 'soil_objectsSerialized{stage="production"} 41 ').
+	count := 42.
+	self assert: ((CanopyPrometheusVisitor new format: root) lines last
+		beginsWith: 'soil_objectsSerialized{stage="production"} 42 ')
+]
+
 { #category : 'as yet unclassified' }
 CanopyMetricsVisitorTest >> testAMetricWithoutLabelsIsWrittenWithoutBraces [
 	"An empty label set used to come out as name{} 1024, because the check was for nil and the