FIR LT: Fix diagnostic location calculation on the last line

it was calculated incorrectly on the last line that do not end
with EOL.
#KT-56649 fixed

compiler/cli/src/org/jetbrains/kotlin/cli/common/fir/FirDiagnosticsCompilerResultsReporter.kt

@@ -166,7 +166,7 @@ private class SequentialFilePositionFinder(file: File) : Closeable {
         fun posInCurrentLine(): KtSourceFilePos? {
             val col = offset - (charsRead - currentLineContent!!.length - 1)/* beginning of line offset */ + 1 /* col is 1-based */
             assert(col > 0)
-            return if (col <= currentLineContent!!.length)
+            return if (col <= currentLineContent!!.length + 1 /* accounting for a report on EOL (e.g. syntax errors) */ )
                 KtSourceFilePos(currentLine, col, if (withLineContents) currentLineContent else null)
             else null
         }
@@ -195,6 +195,8 @@ private class SequentialFilePositionFinder(file: File) : Closeable {
                 bufPos = 0
                 if (bufLength < 0) {
                     endOfStream = true
+                    currentLine++
+                    charsRead++ // assuming virtual EOL at EOF for calculations
                     break
                 }
             } else {

compiler/testData/cli/jvm/firErrorOnLastLine.args

@@ -0,0 +1,6 @@
+$TESTDATA_DIR$/firErrorOnLastLine.kt
+-language-version
+2.0
+-Xuse-fir-lt=true
+-d
+$TEMP_DIR$

compiler/testData/cli/jvm/firErrorOnLastLine.kt

@@ -0,0 +1,2 @@
+val x = this
+val y = this // EOL AFTER THIS LINE!

compiler/testData/cli/jvm/firErrorOnLastLine.out

@@ -0,0 +1,8 @@
+warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
+compiler/testData/cli/jvm/firErrorOnLastLine.kt:1:9: error: 'this' is not defined in this context
+val x = this
+        ^
+compiler/testData/cli/jvm/firErrorOnLastLine.kt:2:9: error: 'this' is not defined in this context
+val y = this // EOL AFTER THIS LINE!
+        ^
+COMPILATION_ERROR

compiler/testData/cli/jvm/firErrorOnLastLineNoEol.args

@@ -0,0 +1,6 @@
+$TESTDATA_DIR$/firErrorOnLastLineNoEol.kt
+-language-version
+2.0
+-Xuse-fir-lt=true
+-d
+$TEMP_DIR$

compiler/testData/cli/jvm/firErrorOnLastLineNoEol.kt

@@ -0,0 +1,2 @@
+val x = this
+val y = this // *NO* EOL AFTER THIS LINE!

compiler/testData/cli/jvm/firErrorOnLastLineNoEol.out

@@ -0,0 +1,8 @@
+warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
+compiler/testData/cli/jvm/firErrorOnLastLineNoEol.kt:1:9: error: 'this' is not defined in this context
+val x = this
+        ^
+compiler/testData/cli/jvm/firErrorOnLastLineNoEol.kt:2:9: error: 'this' is not defined in this context
+val y = this // *NO* EOL AFTER THIS LINE!
+        ^
+COMPILATION_ERROR

compiler/testData/cli/jvm/firSyntaxError.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/firSyntaxError.kt
+-language-version
+2.0
+-d
+$TEMP_DIR$

compiler/testData/cli/jvm/firSyntaxError.kt

@@ -0,0 +1 @@
+fun a() {

compiler/testData/cli/jvm/firSyntaxError.out

@@ -0,0 +1,5 @@
+warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
+compiler/testData/cli/jvm/firSyntaxError.kt:1:10: error: syntax error
+fun a() {
+         ^
+COMPILATION_ERROR

compiler/tests-gen/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -442,6 +442,16 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/firError.args");
         }
 
+        @TestMetadata("firErrorOnLastLine.args")
+        public void testFirErrorOnLastLine() throws Exception {
+            runTest("compiler/testData/cli/jvm/firErrorOnLastLine.args");
+        }
+
+        @TestMetadata("firErrorOnLastLineNoEol.args")
+        public void testFirErrorOnLastLineNoEol() throws Exception {
+            runTest("compiler/testData/cli/jvm/firErrorOnLastLineNoEol.args");
+        }
+
         @TestMetadata("firHello.args")
         public void testFirHello() throws Exception {
             runTest("compiler/testData/cli/jvm/firHello.args");
@@ -492,6 +502,11 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/firStdlibDependency.args");
         }
 
+        @TestMetadata("firSyntaxError.args")
+        public void testFirSyntaxError() throws Exception {
+            runTest("compiler/testData/cli/jvm/firSyntaxError.args");
+        }
+
         @TestMetadata("firVsClassicAnnotation.args")
         public void testFirVsClassicAnnotation() throws Exception {
             runTest("compiler/testData/cli/jvm/firVsClassicAnnotation.args");