Trim function params in TemplateExpander

There is a MacOS integration test that checks that we're trimming before
looking up labels, but it only checks for genrules, which aren't using this
code path yet.

This was changed in 1a8d6b8 and we could see breakages in non-genrule
usage if a release picks up that change but not this.

PiperOrigin-RevId: 173393718

src/main/java/com/google/devtools/build/lib/analysis/stringtemplate/TemplateExpander.java

@@ -90,7 +90,8 @@ private String expand(TemplateContext context, int depth) throws ExpansionExcept
             result.append(value);
           } else {
             String name = var.substring(0, spaceIndex);
-            String param = var.substring(spaceIndex + 1);
+            // Trim the string to remove leading and trailing whitespace.
+            String param = var.substring(spaceIndex + 1).trim();
             String value = context.lookupFunction(name, param);
             result.append(value);
           }

src/test/java/com/google/devtools/build/lib/analysis/stringtemplate/TemplateExpanderTest.java

@@ -200,4 +200,11 @@ public void testDollarDollar() throws Exception {
     assertThat(expand("$${file%:.*8}")).isEqualTo("${file%:.*8}");
     assertThat(expand("$$(basename file)")).isEqualTo("$(basename file)");
   }
+
+  // Regression test: check that the parameter is trimmed before expanding.
+  @Test
+  public void testFunctionExpansionIsTrimmed() throws Exception {
+    context.functions.put("foo", (String p) -> "FOO(" + p + ")");
+    assertThat(expand("$(foo  baz )")).isEqualTo("FOO(baz)");
+  }
 }