[clang-format] Fix an assertion failure on -lines=0:n

Also fixed the error message for start line > end line and added test cases.

Fixes #56438.

Differential Revision: https://reviews.llvm.org/D129348

Author: owenca

clang/test/Format/line-ranges.cpp

@@ -9,3 +9,11 @@ int  *  i;
 
 // CHECK: {{^int\ \*i;$}}
 int   *   i;
+
+// RUN: not clang-format -lines=0:1 < %s 2>&1 \
+// RUN:   | FileCheck -strict-whitespace -check-prefix=CHECK0 %s
+// CHECK0: error: start line should be at least 1
+
+// RUN: not clang-format -lines=2:1 < %s 2>&1 \
+// RUN:   | FileCheck -strict-whitespace -check-prefix=CHECK1 %s
+// CHECK1: error: start line should not exceed end line

clang/tools/clang-format/ClangFormat.cpp

@@ -246,8 +246,12 @@ static bool fillRanges(MemoryBuffer *Code,
         errs() << "error: invalid <start line>:<end line> pair\n";
         return true;
       }
+      if (FromLine < 1) {
+        errs() << "error: start line should be at least 1\n";
+        return true;
+      }
       if (FromLine > ToLine) {
-        errs() << "error: start line should be less than end line\n";
+        errs() << "error: start line should not exceed end line\n";
         return true;
       }
       SourceLocation Start = Sources.translateLineCol(ID, FromLine, 1);