Indent inside strings after line-ending backslash

rust-mode-tests.el

@@ -284,8 +284,8 @@ very very very long string
  */"
    ))
 
-(defun test-indent (indented)
-  (let ((deindented (replace-regexp-in-string "^[[:blank:]]*" "      " indented)))
+(defun test-indent (indented &optional deindented)
+  (let ((deindented (or deindented (replace-regexp-in-string "^[[:blank:]]*" "      " indented))))
     (rust-test-manip-code
      deindented
      1
@@ -1207,3 +1207,122 @@ impl Foo for Bar {
 }
 "
    ))
+
+(ert-deftest test-indent-string-with-eol-backslash ()
+  (test-indent
+   "
+pub fn foo() {
+    format!(\"abc \\
+             def\")
+}
+"
+   ))
+
+(ert-deftest test-indent-string-with-eol-backslash-at-start ()
+  (test-indent
+   "
+pub fn foo() {
+    format!(\"\\
+        abc \\
+        def\")
+}
+"
+   ))
+
+(ert-deftest test-indent-string-without-eol-backslash-indent-is-not-touched ()
+  (test-indent
+   "
+pub fn foo() {
+    format!(\"
+abc
+def\");
+}
+
+pub fn foo() {
+    format!(\"la la la
+la
+la la\");
+}
+"
+   ;; Should still indent the code parts but leave the string internals alone:
+   "
+         pub fn foo() {
+    format!(\"
+abc
+def\");
+}
+
+pub fn foo() {
+    format!(\"la la la
+la
+la la\");
+   }
+"
+   ))
+
+(ert-deftest test-indent-string-eol-backslash-mixed-with-literal-eol ()
+  (test-indent
+   "
+fn foo() {
+    println!(\"
+Here is the beginning of the string
+            and here is a line that is arbitrarily indented \\
+            and a continuation of that indented line
+     and another arbitrary indentation
+  still another
+        yet another \\
+        with a line continuing it
+And another line not indented
+\")
+}
+"
+   "
+fn foo() {
+    println!(\"
+Here is the beginning of the string
+            and here is a line that is arbitrarily indented \\
+            and a continuation of that indented line
+     and another arbitrary indentation
+  still another
+        yet another \\
+with a line continuing it
+And another line not indented
+\")
+}
+"))
+
+(ert-deftest test-indent-string-eol-backslash-dont-touch-raw-strings ()
+  (test-indent
+   "
+pub fn foo() {
+    format!(r\"\
+abc\
+         def\");
+}
+
+pub fn foo() {
+    format!(r\"la la la
+    la\
+la la\");
+}
+"
+   ;; Should still indent the code parts but leave the string internals alone:
+   "
+    pub fn foo() {
+    format!(r\"\
+abc\
+         def\");
+}
+
+pub fn foo() {
+          format!(r\"la la la
+    la\
+la la\");
+}
+"
+   ))
+
+(ert-deftest indent-inside-string-first-line ()
+  (test-indent
+   ;; Needs to leave 1 space before "world"
+   "\"hello \\\n world\""))

rust-mode.el

@@ -117,7 +117,7 @@
     ;; be undone via tab.
 
     (when (looking-at (concat "\s*\." rust-re-ident))
-      (previous-logical-line)
+      (forward-line -1)
       (end-of-line)
 
       (let
@@ -164,10 +164,58 @@
                       (when rust-indent-method-chain
                         (rust-align-to-method-chain))
                       (save-excursion
+                        (rust-rewind-irrelevant)
                         (backward-up-list)
                         (rust-rewind-to-beginning-of-current-level-expr)
                         (+ (current-column) rust-indent-offset))))))
              (cond
+              ;; Indent inside a non-raw string only if the the previous line
+              ;; ends with a backslash that is is inside the same string
+              ((nth 3 (syntax-ppss))
+               (let*
+                   ((string-begin-pos (nth 8 (syntax-ppss)))
+                    (end-of-prev-line-pos (when (> (line-number-at-pos) 1)
+                                            (save-excursion
+                                              (forward-line -1)
+                                              (end-of-line)
+                                              (point)))))
+                 (when
+                     (and
+                      ;; If the string begins with an "r" it's a raw string and
+                      ;; we should not change the indentation
+                      (/= ?r (char-after string-begin-pos))
+
+                      ;; If we're on the first line this will be nil and the
+                      ;; rest does not apply
+                      end-of-prev-line-pos
+
+                      ;; The end of the previous line needs to be inside the
+                      ;; current string...
+                      (> end-of-prev-line-pos string-begin-pos)
+
+                      ;; ...and end with a backslash
+                      (= ?\\ (char-before end-of-prev-line-pos)))
+
+                   ;; Indent to the same level as the previous line, or the
+                   ;; start of the string if the previous line starts the string
+                   (if (= (line-number-at-pos end-of-prev-line-pos) (line-number-at-pos string-begin-pos))
+                       ;; The previous line is the start of the string.
+                       ;; If the backslash is the only character after the
+                       ;; string beginning, indent to the next indent
+                       ;; level.  Otherwise align with the start of the string.
+                       (if (> (- end-of-prev-line-pos string-begin-pos) 2)
+                           (save-excursion
+                             (goto-char (+ 1 string-begin-pos))
+                             (current-column))
+                         baseline)
+
+                     ;; The previous line is not the start of the string, so
+                     ;; match its indentation.
+                     (save-excursion
+                       (goto-char end-of-prev-line-pos)
+                       (back-to-indentation)
+                       (current-column))))))
+
               ;; A function return type is indented to the corresponding function arguments
               ((looking-at "->")
                (save-excursion
@@ -223,13 +271,14 @@
                     ;; so add one additional indent level
                     (+ baseline rust-indent-offset))))))))))
 
-    ;; If we're at the beginning of the line (before or at the current
-    ;; indentation), jump with the indentation change.  Otherwise, save the
-    ;; excursion so that adding the indentations will leave us at the
-    ;; equivalent position within the line to where we were before.
-    (if (<= (current-column) (current-indentation))
-        (indent-line-to indent)
-      (save-excursion (indent-line-to indent)))))
+    (when indent
+      ;; If we're at the beginning of the line (before or at the current
+      ;; indentation), jump with the indentation change.  Otherwise, save the
+      ;; excursion so that adding the indentations will leave us at the
+      ;; equivalent position within the line to where we were before.
+      (if (<= (current-column) (current-indentation))
+          (indent-line-to indent)
+        (save-excursion (indent-line-to indent))))))
 
 
 ;; Font-locking definitions and helpers