replace with z and remove z when optimal

docs/03-plugins/convert-path-data.mdx

@@ -18,6 +18,9 @@ svgo:
     lineShorthands:
       description: If to convert regular lines to an explicit horizontal or vertical line where possible.
       default: true
+    convertToZ:
+      description: If to convert lines that go to the start to a `z` command.
+      default: true
     curveSmoothShorthands:
       description: If to convert curves to smooth curves where possible.
       default: true
@@ -55,6 +58,7 @@ This plugin uses multiple techniques to either reduce the number of instructions
 
 * Convert between relative or absolute coordinates, whichever is shortest.
 * Convert between commands. For example, a bézier curve that behaves like a straight line might as well use a line instruction.
+* Remove commands (when applicable). For example, a command that moves to the current position can be removed.
 * Trim redundant delimiters and leading zeros.
 * Round numeric values using conventional rounding rules.
 

plugins/convertPathData.js

@@ -46,6 +46,7 @@ let arcTolerance;
  *   },
  *   straightCurves: boolean,
  *   lineShorthands: boolean,
+ *   convertToZ: boolean,
  *   curveSmoothShorthands: boolean,
  *   floatPrecision: number | false,
  *   transformPrecision: number,
@@ -95,6 +96,7 @@ exports.fn = (root, params) => {
     },
     straightCurves = true,
     lineShorthands = true,
+    convertToZ = true,
     curveSmoothShorthands = true,
     floatPrecision = 3,
     transformPrecision = 5,
@@ -116,6 +118,7 @@ exports.fn = (root, params) => {
     makeArcs,
     straightCurves,
     lineShorthands,
+    convertToZ,
     curveSmoothShorthands,
     floatPrecision,
     transformPrecision,
@@ -167,6 +170,14 @@ exports.fn = (root, params) => {
             (computedStyle['stroke-linecap'].type === 'dynamic' ||
               computedStyle['stroke-linecap'].value !== 'butt');
           const maybeHasStrokeAndLinecap = maybeHasStroke && maybeHasLinecap;
+          // TODO: when stroke is used, prefer z more
+          // Z is the same as going home at 90 and 0 degrees, but not at other degrees
+          const isSafeToUseZ = maybeHasStroke
+            ? computedStyle['stroke-linecap']?.type === 'static' &&
+              computedStyle['stroke-linecap'].value === 'round' &&
+              computedStyle['stroke-linejoin']?.type === 'static' &&
+              computedStyle['stroke-linejoin'].value === 'round'
+            : true;
 
           var data = path2js(node);
 
@@ -175,6 +186,7 @@ exports.fn = (root, params) => {
             convertToRelative(data);
 
             data = filters(data, newParams, {
+              isSafeToUseZ,
               maybeHasStrokeAndLinecap,
               hasMarkerMid,
             });
@@ -371,10 +383,14 @@ const convertToRelative = (pathData) => {
  * @type {(
  *   path: PathDataItem[],
  *   params: InternalParams,
- *   aux: { maybeHasStrokeAndLinecap: boolean, hasMarkerMid: boolean }
+ *   aux: { isSafeToUseZ: boolean, maybeHasStrokeAndLinecap: boolean, hasMarkerMid: boolean }
  * ) => PathDataItem[]}
  */
-function filters(path, params, { maybeHasStrokeAndLinecap, hasMarkerMid }) {
+function filters(
+  path,
+  params,
+  { isSafeToUseZ, maybeHasStrokeAndLinecap, hasMarkerMid }
+) {
   var stringify = data2Path.bind(null, params),
     relSubpoint = [0, 0],
     pathBase = [0, 0],
@@ -664,6 +680,20 @@ function filters(path, params, { maybeHasStrokeAndLinecap, hasMarkerMid }) {
         }
       }
 
+      // convert going home to z
+      // m 0 0 h 5 v 5 l -5 -5 -> m 0 0 h 5 v 5 z
+      if (
+        params.convertToZ &&
+        (isSafeToUseZ || next?.command === 'Z' || next?.command === 'z') &&
+        (command === 'l' || command === 'h' || command === 'v')
+      ) {
+        // @ts-ignore
+        if (pathBase[0] === item.coords[0] && pathBase[1] === item.coords[1]) {
+          command = 'z';
+          data = [];
+        }
+      }
+
       // collapse repeated commands
       // h 20 h 30 -> h 50
       if (
@@ -806,6 +836,16 @@ function filters(path, params, { maybeHasStrokeAndLinecap, hasMarkerMid }) {
       if (prev.command === 'Z' || prev.command === 'z') return false;
       prev = item;
     }
+    if (
+      (command === 'Z' || command === 'z') &&
+      params.removeUseless &&
+      isSafeToUseZ &&
+      // @ts-ignore
+      item.base[0] === item.coords[0] &&
+      // @ts-ignore
+      item.base[1] === item.coords[1]
+    )
+      return false;
 
     return true;
   });

plugins/plugins-types.ts

@@ -42,6 +42,7 @@ type DefaultPlugins = {
     };
     straightCurves?: boolean;
     lineShorthands?: boolean;
+    convertToZ?: boolean;
     curveSmoothShorthands?: boolean;
     floatPrecision?: number | false;
     transformPrecision?: number;
@@ -138,7 +139,7 @@ type DefaultPlugins = {
   moveElemsAttrsToGroup: void;
   moveGroupAttrsToElems: void;
   removeComments: {
-    preservePatterns: Array<RegExp|string> | false
+    preservePatterns: Array<RegExp | string> | false;
   };
   removeDesc: {
     removeAny?: boolean;