Add :max-column-alignment-width option

Add a new :max-column-alignment-width option for column alignment that
selects the anchor by cascade demotion: the largest key for which
every shorter key fits within N spaces. Keys longer than the chosen
anchor are not padded.

Author: sirmspencer

README.md

@@ -316,6 +316,29 @@ In order to load the standard configuration file from Leiningen, add the
    :as everything}                          ;; 27 spaces, falls back to 1 space
   ```
 
+* `:max-column-alignment-width` -
+  a positive integer that limits which keys participate in column
+  alignment. Keys whose end column is at or within N are aligned
+  together; keys that end past column N are not padded and receive a
+  single space before their value. Defaults to nil (no limit).
+  **Experimental.**
+
+  ```clojure
+  ;; Input:
+  {:a 1
+   :abcde 2
+   :abcdefg 3
+   :long-name 4}
+
+  ;; With :align-map-columns? true and :max-column-alignment-width 7:
+  ;; :a and :abcde end at or within column 7 and align together;
+  ;; :abcdefg and :long-name end past column 7 and are not padded
+  {:a     1      ;; ends within column 7, padded to value column
+   :abcde 2      ;; ends at column 7, sets the value column
+   :abcdefg 3    ;; ends past column 7, 1 space
+   :long-name 4} ;; ends past column 7, 1 space
+  ```
+
 * `:blank-lines-separate-alignment?` -
   true if cljfmt should treat blank lines as separators when aligning
   columns. When enabled, alignment groups are separated by blank lines,

cljfmt/src/cljfmt/core.cljc

@@ -383,6 +383,7 @@
    :align-single-column-lines?            false
    :aligned-forms                         default-aligned-forms
    :max-column-alignment-gap              nil
+   :max-column-alignment-width            nil
    :blank-line-forms                      blank-line-forms
    :blank-lines-separate-alignment?       false
    :extra-aligned-forms                   {}
@@ -670,13 +671,16 @@
 (defn- count-spaces [zloc]
   (if (space? zloc) (node-str-length zloc) 0))
 
-(defn- pad-to-position [zloc start-position {max-gap :max-column-alignment-gap}]
-  {:pre [(or (nil? max-gap) (pos-int? max-gap))]}
-  (let [delta (- start-position (margin zloc))]
-    (if max-gap
-      (let [old-gap (count-spaces (z/left* zloc))
-            new-gap (+ old-gap delta)]
-        (pad-node zloc (if (> new-gap max-gap) (- 1 old-gap) delta)))
+(defn- pad-to-position [zloc start-position {max-gap     :max-column-alignment-gap
+                                             align-width :max-column-alignment-width}]
+  {:pre [(or (nil? max-gap) (pos-int? max-gap))
+         (or (nil? align-width) (pos-int? align-width))]}
+  (let [old-gap (count-spaces (z/left* zloc))
+        delta   (- start-position (margin zloc))
+        new-gap (+ old-gap delta)]
+    (if (or (< new-gap 1)
+            (and max-gap (> new-gap max-gap)))
+      (pad-node zloc (- 1 old-gap))
       (pad-node zloc delta))))
 
 (defn- edit-column [zloc column f]
@@ -707,17 +711,23 @@
           (recur (z/right* zloc) 0 acc)
           (recur (z/right* zloc) (inc col) (f zloc col acc)))))))
 
-(defn- column-start-position [zloc col opts]
-  (let [reduce-fn (if (:blank-lines-separate-alignment? opts)
+(defn- column-start-position
+  [zloc col {align-width    :max-column-alignment-width
+             align-singles? :align-single-column-lines?
+             separate?      :blank-lines-separate-alignment?}]
+  (let [reduce-fn (if separate?
                     reduce-column-group
                     reduce-columns)
-        maximizer (fn [zloc c max-pos]
+        collector (fn [zloc c positions]
                     (if (and (= c (dec col))
-                             (or (:align-single-column-lines? opts)
+                             (or align-singles?
                                  (not (single-column-line? zloc))))
-                      (max max-pos (node-end-position zloc))
-                      max-pos))]
-    (inc (reduce-fn zloc maximizer 0))))
+                      (conj positions (node-end-position zloc))
+                      positions))
+        positions (reduce-fn zloc collector [])]
+    (inc (apply max 0 (if align-width
+                        (filter #(<= % (+ (apply min 0 positions) align-width)) positions)
+                        positions)))))
 
 (defn- align-one-column
   [zloc col {:keys [blank-lines-separate-alignment?] :as opts}]

cljfmt/test/cljfmt/core_test.cljc

@@ -3193,6 +3193,47 @@
          {:align-map-columns?       true
           :max-column-alignment-gap 5}))))
 
+(deftest test-max-column-alignment-width
+  (testing "form: anchor demoted until all keys fit within gap"
+    (is (reformats-to?
+         ["(let [a 1"
+          "      abcde 2"
+          "      abcdefg 3"
+          "      long-name 4]"
+          "  [a abcde abcdefg long-name])"]
+         ["(let [a     1"
+          "      abcde 2"
+          "      abcdefg 3"
+          "      long-name 4]"
+          "  [a abcde abcdefg long-name])"]
+         {:align-form-columns?        true
+          :max-column-alignment-width 11})))
+  (testing "map: anchor demoted until all keys fit within gap"
+    (is (reformats-to?
+         ["{:a \"x\""
+          " :abcde \"y\""
+          " :abcdefg \"z\""
+          " :long-key \"w\"}"]
+         ["{:a     \"x\""
+          " :abcde \"y\""
+          " :abcdefg \"z\""
+          " :long-key \"w\"}"]
+         {:align-map-columns?         true
+          :max-column-alignment-width 7})))
+  (testing "composing both flags refines alignment further"
+    (is (reformats-to?
+         ["{:x \"a\""
+          " :abc \"b\""
+          " :abcde \"c\""
+          " :long-key \"d\"}"]
+         ["{:x \"a\""
+          " :abc   \"b\""
+          " :abcde \"c\""
+          " :long-key \"d\"}"]
+         {:align-map-columns?         true
+          :max-column-alignment-width 7
+          :max-column-alignment-gap   3}))))
+
 (deftest test-realign-form
   (is (= "
 {:x   1