Introduce smart trimming to fix #37

Author: fatfisz

src/stripIndent/stripIndent.js

@@ -4,7 +4,7 @@ import trimResultTransformer from '../trimResultTransformer';
 
 const stripIndent = createTag(
   stripIndentTransformer(),
-  trimResultTransformer(),
+  trimResultTransformer('smart'),
 );
 
 export default stripIndent;

src/stripIndentTransformer/stripIndentTransformer.test.js

@@ -6,7 +6,7 @@ import { readFromFixture } from '../testUtils';
 test('default behaviour removes the leading indent, but preserves the rest', () => {
   const stripIndent = createTag(
     stripIndentTransformer(),
-    trimResultTransformer(),
+    trimResultTransformer('smart'),
   );
   const expected = readFromFixture(__dirname, 'stripIndent');
   const actual = stripIndent`
@@ -21,7 +21,7 @@ test('default behaviour removes the leading indent, but preserves the rest', ()
 test('type "initial" does not remove indents if there is no need to do so', () => {
   const stripIndent = createTag(
     stripIndentTransformer(),
-    trimResultTransformer(),
+    trimResultTransformer('smart'),
   );
   expect(stripIndent``).toBe('');
   expect(stripIndent`foo`).toBe('foo');
@@ -31,7 +31,7 @@ test('type "initial" does not remove indents if there is no need to do so', () =
 test('removes all indents if type is "all"', () => {
   const stripIndents = createTag(
     stripIndentTransformer('all'),
-    trimResultTransformer(),
+    trimResultTransformer('smart'),
   );
   const expected = readFromFixture(__dirname, 'stripIndents');
   const actual = stripIndents`

src/stripIndents/stripIndents.js

@@ -4,7 +4,7 @@ import trimResultTransformer from '../trimResultTransformer';
 
 const stripIndents = createTag(
   stripIndentTransformer('all'),
-  trimResultTransformer(),
+  trimResultTransformer('smart'),
 );
 
 export default stripIndents;

src/trimResultTransformer/trimResultTransformer.js

@@ -1,4 +1,4 @@
-const supportedSides = ['', 'start', 'left', 'end', 'right'];
+const supportedSides = ['', 'start', 'left', 'end', 'right', 'smart'];
 
 /**
  * TemplateTag transformer that trims whitespace on the end result of a tagged template
@@ -23,6 +23,9 @@ const trimResultTransformer = (side = '') => {
         case 'end':
         case 'right':
           return endResult.replace(/\s*$/, '');
+
+        case 'smart':
+          return endResult.replace(/[^\S\n]+$/gm, '').replace(/^\n/, '');
       }
     },
   };

src/trimResultTransformer/trimResultTransformer.test.js

@@ -36,6 +36,34 @@ test('can be used sequentially', () => {
   expect(trimStart`  bar  `).toBe('bar  ');
 });
 
+describe('smart trimming', () => {
+  const trimSmart = createTag(trimResultTransformer('smart'));
+
+  test('leaves a string without surrounding whitespace as-is', () => {
+    expect(trimSmart`a`).toBe('a');
+  });
+
+  test('performs an end-side trim on a single-line string', () => {
+    expect(trimSmart`  a  `).toBe('  a');
+  });
+
+  test('trims whitespace at the end of each line', () => {
+    expect(trimSmart`a  \n  b  \nc  `).toBe('a\n  b\nc');
+  });
+
+  test("removes the first line if it's empty", () => {
+    expect(trimSmart`  \na`).toBe('a');
+  });
+
+  test('leaves the trailing newline character', () => {
+    expect(trimSmart`a  \n`).toBe('a\n');
+  });
+
+  test("doesn't remove intentional newline characters", () => {
+    expect(trimSmart`a\n  \n`).toBe('a\n\n');
+  });
+});
+
 test('throws an error if invalid side supplied', () => {
   expect(() => {
     trimResultTransformer('up');