Implement substring formatting with fmt

private/refactoring-result.rkt

@@ -27,7 +27,10 @@
 
 (require fancy-app
          fmt
+         guard
+         (only-in racket/list last)
          racket/match
+         racket/string
          rebellion/base/immutable-string
          rebellion/base/range
          rebellion/base/symbol
@@ -42,6 +45,11 @@
          resyntax/private/syntax-replacement)
 
 
+(module+ test
+  (require (submod "..")
+           rackunit))
+
+
 ;@----------------------------------------------------------------------------------------------------
 
 
@@ -104,39 +112,21 @@
 ;; This function is the sole integration point between Resyntax and fmt. It is used by Resyntax to
 ;; format any refactored code initially generated by Resyntax.
 (define (format-refactored-code refactored-source-code #:start start #:end end)
-  ;; TODO: actually use start and end to format only that range once fmt supports it.
-  (define formatted-source-code
-    ;; Appending a newline is needed because fmt strips the trailing newline from files for some
-    ;; reason.
-    (string-append (program-format refactored-source-code) "\n"))
+  (define changed-code-substring (substring refactored-source-code start end))
+  (define initial-columns (string-column-offset refactored-source-code start))
+  (define formatted-code-substring
+    (program-format changed-code-substring #:indent initial-columns))
 
   ;; Formatting can change the total length of the program source code, and we want to tell the
   ;; caller where the new endpoint of the formatted source range is.
   (define formatting-delta
-    (- (string-length formatted-source-code) (string-length refactored-source-code)))
+    (- (string-length formatted-code-substring) (string-length changed-code-substring)))
   (define end-after-formatting (+ end formatting-delta))
 
-  ;; Before handing the reformatted code back to the caller, we double check that fmt didn't touch
-  ;; anything outside the requested range. If it did, raise an exception with an error message that
-  ;; explains the problem and includes the code both before and after formatting.
-  (unless (and (equal? (substring refactored-source-code 0 start)
-                       (substring formatted-source-code 0 start))
-               (equal? (substring refactored-source-code end)
-                       (substring formatted-source-code end-after-formatting)))
-    (raise
-     (exn:fail:refactoring-formatting-out-of-bounds
-      (string-append "format-refactored-code: failed to format refactored code;\n"
-                     " fmt edited other code outside the target source code range\n"
-                     (format "  code before formatting:\n~a\n"
-                             (string-indent refactored-source-code #:amount 3))
-                     (format "  code after formatting:\n~a\n"
-                             (string-indent formatted-source-code #:amount 3))
-                     (format "  target source range: [~a, ~a)" start end))
-      (current-continuation-marks)
-      refactored-source-code
-      formatted-source-code
-      start
-      end)))
+  (define formatted-source-code
+    (string-append (substring refactored-source-code 0 start)
+                   formatted-code-substring
+                   (substring refactored-source-code end)))
 
   (formatted-code-subrange formatted-source-code start end-after-formatting))
 
@@ -217,3 +207,29 @@
                 (sub1 (linemap-position-to-start-of-line map start))
                 (sub1 (linemap-position-to-end-of-line map formatted-end)))))
   (in-lines (open-input-string replacement-text)))
+
+
+(define/guard (string-column-offset str position)
+  (define up-to-position (substring str 0 position))
+  (guard (non-empty-string? up-to-position) #:else 0)
+  (string-length (last (string-split up-to-position "\n" #:trim? #false))))
+
+
+(module+ test
+  (test-case "string-column-offset"
+    (check-equal? (string-column-offset "" 0) 0)
+    (check-equal? (string-column-offset "apple" 0) 0)
+    (check-equal? (string-column-offset "apple" 4) 4)
+    (check-equal? (string-column-offset "apple\nbanana" 0) 0)
+    (check-equal? (string-column-offset "apple\nbanana" 4) 4)
+    (check-equal? (string-column-offset "apple\nbanana" 6) 0)
+    (check-equal? (string-column-offset "apple\nbanana" 8) 2)
+    (check-equal? (string-column-offset "apple\nbanana" 12) 6)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 0) 0)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 4) 4)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 6) 0)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 8) 2)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 12) 6)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 13) 0)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 16) 3)
+    (check-equal? (string-column-offset "apple\nbanana\ngrape" 18) 5)))