fix: add adaptive font sizing for complex treemaps

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

.changeset/legal-apples-wink.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Ensure treemap labels render correctly in large nested diagrams

cypress/integration/rendering/treemap.spec.ts

@@ -468,4 +468,65 @@ classDef highlight fill:#f39c12,color:#000,stroke:#e67e22,stroke-width:2px;
     );
   });
   */
+
+  it('14: should render labels in complex treemap with many nested blocks', () => {
+    imgSnapshotTest(
+      `treemap-beta
+    "🔴 High Activity (Top 50%)":::redContainer
+        "packages/app (1115)": 15:::redleaf
+        "packages/app/src (844)": 12:::redleaf
+        "packages/app/src/lib (707)": 11:::redleaf
+        "packages/app/src/routes (353)": 7:::redleaf
+        "packages/app/tests (277)": 6:::redleaf
+        "packages/app/tests/e2e (245)": 6:::redleaf
+        "packages/app/tests/common (48)": 4:::redleaf
+        "packages/llm-prompts (29)": 3:::redleaf
+        "packages/emails (26)": 3:::redleaf
+        "packages/app/tests/api (23)": 3:::redleaf
+        "packages/emails/src (18)": 3:::redleaf
+        "packages/emails/src/emails (17)": 3:::redleaf
+        "packages/app/static (15)": 3:::redleaf
+        "packages/llm-prompts/diagram-chat (15)": 3:::redleaf
+        "packages/app/prisma (11)": 3:::redleaf
+        "packages/app/prisma/migrations (11)": 3:::redleaf
+        "packages/llm-prompts/shared (9)": 3:::redleaf
+        "packages/app/static/icons (8)": 3:::redleaf
+        "packages/emails/src/components (8)": 3:::redleaf
+        "packages/app-observability (8)": 3:::redleaf
+        "packages/mermaid-pre-render-server (8)": 3:::redleaf
+    "🟠 Medium Activity (35%)":::orangeContainer
+        "packages/app/tests/mobile (6)": 3:::orangeleaf
+        "packages/llm-prompts/diagram-chat/tests (6)": 3:::orangeleaf
+        "packages/eslint-plugin (6)": 3:::orangeleaf
+        "packages/eslint-plugin/src (5)": 3:::orangeleaf
+        "packages/eslint-plugin/src/rules (5)": 3:::orangeleaf
+        "packages/app/static/img (4)": 3:::orangeleaf
+        "packages/llm-prompts/tests (4)": 3:::orangeleaf
+        "packages/llm-prompts/common (3)": 3:::orangeleaf
+        "packages/mermaid-pre-render-server/tests (3)": 3:::orangeleaf
+        "packages/mermaid-pre-render-server/tests/e2e (3)": 3:::orangeleaf
+        "packages/app/tests/seed (2)": 3:::orangeleaf
+        "packages/llm-prompts/shared/patches (2)": 3:::orangeleaf
+        "packages/mermaid-pre-render-server/src (2)": 3:::orangeleaf
+        "packages/app/scripts (1)": 3:::orangeleaf
+    "🟡 Low Activity (15%)":::yellowContainer
+        "packages/llm-prompts/regenerate-diagram (1)": 3:::yellowleaf
+        "packages/llm-prompts/repair-diagram (1)": 3:::yellowleaf
+        "packages/app-buildship (1)": 3:::yellowleaf
+        "packages/app-buildship/src (1)": 3:::yellowleaf
+        "packages/app-buildship/src/cleanupAssets (1)": 3:::yellowleaf
+        "packages/icons (1)": 3:::yellowleaf
+
+classDef root fill:#F5BA71
+classDef redContainer fill:#F54927
+classDef orangeContainer fill:#DE8118
+classDef yellowContainer fill:#F5E514
+
+classDef redleaf fill:#F54927,stroke:none,color:#FFFFFF
+classDef orangeleaf fill:#DE8118,stroke:none,color:#FFFFFF
+classDef yellowleaf fill:#F5E514,stroke:none,color:#333333
+      `,
+      {}
+    );
+  });
 });

packages/mermaid/src/diagrams/treemap/renderer.ts

@@ -224,6 +224,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
     .attr('dominant-baseline', 'middle')
     .text((d) => (d.depth === 0 ? '' : d.data.name)) // Skip label for root section
     .attr('font-weight', 'bold')
+    .attr('clip-path', (_d, i) => `url(#clip-section-${id}-${i})`) // Apply clip-path to prevent overflow
     .attr('style', (d) => {
       // Hide the label for the root section
       if (d.depth === 0) {
@@ -309,6 +310,17 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
 
   // Draw the leaf nodes
   const leafNodes = treemapData.leaves();
+
+  const isComplexTreemap = leafNodes.length > 20;
+
+  const baseLabelFontSize = isComplexTreemap ? 16 : 38;
+  const baseValueFontSize = isComplexTreemap ? 14 : 28;
+  const minLabelFontSize = isComplexTreemap ? 4 : 8;
+  const minValueFontSize = isComplexTreemap ? 4 : 6;
+  const labelPadding = isComplexTreemap ? 2 : 4;
+  const minDisplayThreshold = isComplexTreemap ? 8 : 10;
+  const spacingBetweenLabelAndValue = isComplexTreemap ? 1 : 2;
+
   const cell = g
     .selectAll('.treemapLeafGroup')
     .data(leafNodes)
@@ -359,7 +371,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
     // .style('fill', (d) => colorScaleLabel(d.data.name))
     .attr('style', (d) => {
       const labelStyles =
-        'text-anchor: middle; dominant-baseline: middle; font-size: 38px;fill:' +
+        `text-anchor: middle; dominant-baseline: middle; font-size: ${baseLabelFontSize}px;fill:` +
         colorScaleLabel(d.data.name) +
         ';';
       const styles = styles2String({ cssCompiledStyles: d.data.cssCompiledStyles } as Node);
@@ -374,21 +386,16 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
     const nodeHeight = d.y1 - d.y0;
     const textNode = self.node()!;
 
-    const padding = 4;
-    const availableWidth = nodeWidth - 2 * padding;
-    const availableHeight = nodeHeight - 2 * padding;
+    const availableWidth = nodeWidth - 2 * labelPadding;
+    const availableHeight = nodeHeight - 2 * labelPadding;
 
-    if (availableWidth < 10 || availableHeight < 10) {
+    if (availableWidth < minDisplayThreshold || availableHeight < minDisplayThreshold) {
       self.style('display', 'none');
       return;
     }
 
     let currentLabelFontSize = parseInt(self.style('font-size'), 10);
-    const minLabelFontSize = 8;
-    const originalValueRelFontSize = 28; // Original font size of value, for max cap
     const valueScaleFactor = 0.6; // Value font size as a factor of label font size
-    const minValueFontSize = 6;
-    const spacingBetweenLabelAndValue = 2;
 
     // 1. Adjust label font size to fit width
     while (
@@ -402,7 +409,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
     // 2. Adjust both label and prospective value font size to fit combined height
     let prospectiveValueFontSize = Math.max(
       minValueFontSize,
-      Math.min(originalValueRelFontSize, Math.round(currentLabelFontSize * valueScaleFactor))
+      Math.min(baseValueFontSize, Math.round(currentLabelFontSize * valueScaleFactor))
     );
     let combinedHeight =
       currentLabelFontSize + spacingBetweenLabelAndValue + prospectiveValueFontSize;
@@ -411,7 +418,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
       currentLabelFontSize--;
       prospectiveValueFontSize = Math.max(
         minValueFontSize,
-        Math.min(originalValueRelFontSize, Math.round(currentLabelFontSize * valueScaleFactor))
+        Math.min(baseValueFontSize, Math.round(currentLabelFontSize * valueScaleFactor))
       );
       if (
         prospectiveValueFontSize < minValueFontSize &&
@@ -432,13 +439,18 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
     self.style('font-size', `${currentLabelFontSize}px`);
 
     // 3. Final visibility check for the label
-    if (
-      textNode.getComputedTextLength() > availableWidth ||
-      currentLabelFontSize < minLabelFontSize ||
-      availableHeight < currentLabelFontSize
-    ) {
-      self.style('display', 'none');
-      // If label is hidden, value will be hidden by its own .each() loop
+    if (isComplexTreemap) {
+      if (currentLabelFontSize < minLabelFontSize || availableHeight < minLabelFontSize) {
+        self.style('display', 'none');
+      }
+    } else {
+      if (
+        textNode.getComputedTextLength() > availableWidth ||
+        currentLabelFontSize < minLabelFontSize ||
+        availableHeight < currentLabelFontSize
+      ) {
+        self.style('display', 'none');
+      }
     }
   });
 
@@ -454,7 +466,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
       })
       .attr('style', (d) => {
         const labelStyles =
-          'text-anchor: middle; dominant-baseline: hanging; font-size: 28px;fill:' +
+          `text-anchor: middle; dominant-baseline: hanging; font-size: ${baseValueFontSize}px;fill:` +
           colorScaleLabel(d.data.name) +
           ';';
         const styles = styles2String({ cssCompiledStyles: d.data.cssCompiledStyles } as Node);
@@ -481,14 +493,11 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
       }
 
       const finalLabelFontSize = parseFloat(labelElement.style('font-size'));
-      const originalValueFontSize = 28; // From initial style setting
       const valueScaleFactor = 0.6;
-      const minValueFontSize = 6;
-      const spacingBetweenLabelAndValue = 2;
 
       const actualValueFontSize = Math.max(
         minValueFontSize,
-        Math.min(originalValueFontSize, Math.round(finalLabelFontSize * valueScaleFactor))
+        Math.min(baseValueFontSize, Math.round(finalLabelFontSize * valueScaleFactor))
       );
       valueTextElement.style('font-size', `${actualValueFontSize}px`);
 
@@ -500,7 +509,7 @@ const draw: DrawDefinition = (_text, id, _version, diagram: Diagram) => {
       const nodeTotalHeight = d.y1 - d.y0;
       const cellBottomPadding = 4;
       const maxValueBottomY = nodeTotalHeight - cellBottomPadding;
-      const availableWidthForValue = nodeWidth - 2 * 4; // padding for value text
+      const availableWidthForValue = nodeWidth - 2 * labelPadding;
 
       if (
         valueTextElement.node()!.getComputedTextLength() > availableWidthForValue ||