Currently, the unmet dependency warnings end up with endlessly long
expressions, most of which are false positives.

Here is test code to demonstrate how it currently works.

[Test Case]

  config DEP1
          def_bool y

  config DEP2
          def_bool n

  config A
          bool "A"
          select E

  config B
          bool "B"
          depends on DEP2
          select E

  config C
          bool "C"
          depends on DEP1 && DEP2
          select E

  config D
          def_bool n
          select E

  config E
          bool
          depends on DEP1 && DEP2

[Result]

  $ make allyesconfig
  scripts/kconfig/conf  --allyesconfig Kconfig
  warning: (A && B && D) selects E which has unmet direct
  dependencies (DEP1 && DEP2)

Here, I see some points to be improved.

First, '(A || B || D)' would make more sense than '(A && B && D)'.
I am not sure if this is intentional, but expr_simplify_unmet_dep()
turns OR expressions into AND, like follows:

        case E_OR:
                return expr_alloc_and(

Second, we see false positives.  'A' is a real unmet dependency.
'B' is false positive because 'DEP1' is fixed to 'y', and 'B' depends
on 'DEP2'.  'C' was correctly dropped by expr_simplify_unmet_dep().
'D' is also false positive because it has no chance to be enabled.
Current expr_simplify_unmet_dep() cannot avoid those false positives.

After all, I decided to use the same helpers as used for printing
reverse dependencies in the help.

With this commit, unreadable warnings in the real world:

$ make ARCH=score allyesconfig
scripts/kconfig/conf  --allyesconfig Kconfig
warning: (HWSPINLOCK_QCOM && AHCI_MTK && STMMAC_PLATFORM && DWMAC_IPQ806X
&& DWMAC_LPC18XX && DWMAC_OXNAS && DWMAC_ROCKCHIP && DWMAC_SOCFPGA && DWMA
C_STI && TI_CPSW && PINCTRL_GEMINI && PINCTRL_OXNAS && PINCTRL_ROCKCHIP &&
 PINCTRL_DOVE && PINCTRL_ARMADA_37XX && PINCTRL_STM32 && S3C2410_WATCHDOG
&& VIDEO_OMAP3 && VIDEO_S5P_FIMC && USB_XHCI_MTK && RTC_DRV_AT91SAM9 && LP
C18XX_DMAMUX && VIDEO_OMAP4 && COMMON_CLK_GEMINI && COMMON_CLK_ASPEED && C
OMMON_CLK_NXP && COMMON_CLK_OXNAS && COMMON_CLK_BOSTON && ATMEL_ST && QCOM
_ADSP_PIL && QCOM_Q6V5_PIL && QCOM_GSBI && ATMEL_EBI && ST_IRQCHIP && RESE
T_IMX7 && PHY_HI6220_USB && PHY_RALINK_USB && PHY_ROCKCHIP_PCIE && PHY_DA8
XX_USB) selects MFD_SYSCON which has unmet direct dependencies (HAS_IOMEM)
warning: (PINCTRL_AT91 && PINCTRL_AT91PIO4 && PINCTRL_OXNAS && PINCTRL_PIS
TACHIO && PINCTRL_PIC32 && PINCTRL_MESON && PINCTRL_NOMADIK && PINCTRL_MTK
 && PINCTRL_MT7622 && GPIO_TB10X) selects OF_GPIO which has unmet direct d
ependencies (GPIOLIB && OF && HAS_IOMEM)
warning: (FAULT_INJECTION_STACKTRACE_FILTER && LATENCYTOP && LOCKDEP) sele
cts FRAME_POINTER which has unmet direct dependencies (DEBUG_KERNEL && (CR
IS || M68K || FRV || UML || SUPERH || BLACKFIN || MN10300 || METAG) || ARC
H_WANT_FRAME_POINTERS)

will be turned into:

$ make ARCH=score allyesconfig
scripts/kconfig/conf  --allyesconfig Kconfig

WARNING:
 Unmet direct dependencies detected for MFD_SYSCON
 Depends on:
    HAS_IOMEM [=n]
 Selected by [y]:
  - PINCTRL_STM32 [=y] && PINCTRL [=y] && (ARCH_STM32 || COMPILE_TEST [=y])
&& OF [=y]
  - RTC_DRV_AT91SAM9 [=y] && RTC_CLASS [=y] && (ARCH_AT91 || COMPILE_TEST
[=y])
  - ATMEL_ST [=y] && GENERIC_CLOCKEVENTS [=y]
  - RESET_IMX7 [=y] && RESET_CONTROLLER [=y]
  - PHY_HI6220_USB [=y] && (ARCH_HISI && ARM64 || COMPILE_TEST [=y])
  - PHY_RALINK_USB [=y] && (RALINK || COMPILE_TEST [=y])
  - PHY_ROCKCHIP_PCIE [=y] && (ARCH_ROCKCHIP && OF [=y] || COMPILE_TEST
[=y])

WARNING:
 Unmet direct dependencies detected for OF_GPIO
 Depends on:
    GPIOLIB [=y] && OF [=y] && HAS_IOMEM [=n]
 Selected by [y]:
  - PINCTRL_MTK [=y] && PINCTRL [=y] && (ARCH_MEDIATEK || COMPILE_TEST
[=y]) && OF [=y]
  - PINCTRL_MT7622 [=y] && PINCTRL [=y] && (ARCH_MEDIATEK || COMPILE_TEST
[=y]) && OF [=y] && (ARM64 || COMPILE_TEST [=y])

WARNING:
 Unmet direct dependencies detected for FRAME_POINTER
 Depends on:
    DEBUG_KERNEL [=y] && (CRIS || M68K || FRV || UML || SUPERH || BLACKFIN
 || MN10300 || METAG) || ARCH_WANT_FRAME_POINTERS [=n]
 Selected by [y]:
  - LATENCYTOP [=y] && DEBUG_KERNEL [=y] && STACKTRACE_SUPPORT [=y] &&
PROC_FS [=y] && !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND &&
!ARC && !X86

Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com>
---

Changes in v2:
  - update test case

 scripts/kconfig/expr.c   | 29 -----------------------------
 scripts/kconfig/expr.h   |  1 -
 scripts/kconfig/symbol.c | 33 +++++++++++++++++++++------------
 3 files changed, 21 insertions(+), 42 deletions(-)

diff --git a/scripts/kconfig/expr.c b/scripts/kconfig/expr.c
index 49376e1..235e179 100644
--- a/scripts/kconfig/expr.c
+++ b/scripts/kconfig/expr.c
@@ -1150,35 +1150,6 @@ expr_get_leftmost_symbol(const struct expr *e)
        return expr_copy(e);
 }
 
-/*
- * Given expression `e1' and `e2', returns the leaf of the longest
- * sub-expression of `e1' not containing 'e2.
- */
-struct expr *expr_simplify_unmet_dep(struct expr *e1, struct expr *e2)
-{
-       struct expr *ret;
-
-       switch (e1->type) {
-       case E_OR:
-               return expr_alloc_and(
-                   expr_simplify_unmet_dep(e1->left.expr, e2),
-                   expr_simplify_unmet_dep(e1->right.expr, e2));
-       case E_AND: {
-               struct expr *e;
-               e = expr_alloc_and(expr_copy(e1), expr_copy(e2));
-               e = expr_eliminate_dups(e);
-               ret = (!expr_eq(e, e1)) ? e1 : NULL;
-               expr_free(e);
-               break;
-               }
-       default:
-               ret = e1;
-               break;
-       }
-
-       return expr_get_leftmost_symbol(ret);
-}
-
 void expr_print(struct expr *e,
                void (*fn)(void *, struct symbol *, const char *),
                void *data, int prevtoken)
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index 8dbf2a4..94a383b 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -305,7 +305,6 @@ struct expr *expr_transform(struct expr *e);
 int expr_contains_symbol(struct expr *dep, struct symbol *sym);
 bool expr_depends_symbol(struct expr *dep, struct symbol *sym);
 struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct 
symbol *sym);
-struct expr *expr_simplify_unmet_dep(struct expr *e1, struct expr *e2);
 
 void expr_fprint(struct expr *e, FILE *out);
 struct gstr; /* forward */
diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
index 0f7eba7..9138b80 100644
--- a/scripts/kconfig/symbol.c
+++ b/scripts/kconfig/symbol.c
@@ -333,6 +333,25 @@ static struct symbol *sym_calc_choice(struct symbol *sym)
        return def_sym;
 }
 
+static void sym_warn_unmet_dependency(struct symbol *sym)
+{
+       struct gstr gs = str_new();
+
+       str_printf(&gs, "\nWARNING:\n");
+       str_printf(&gs, " Unmet direct dependencies detected for %s\n",
+                  sym->name);
+       str_printf(&gs, " Depends on:\n    ");
+       expr_gstr_print(sym->dir_dep.expr, &gs);
+       str_printf(&gs, "\n");
+
+       expr_gstr_print_revdep(sym->rev_dep.expr, &gs, yes,
+                              " Selected by [y]:\n");
+       expr_gstr_print_revdep(sym->rev_dep.expr, &gs, mod,
+                              " Selected by [m]:\n");
+
+       fputs(str_get(&gs), stderr);
+}
+
 void sym_calc_value(struct symbol *sym)
 {
        struct symbol_value newval, oldval;
@@ -414,18 +433,8 @@ void sym_calc_value(struct symbol *sym)
                                }
                        }
                calc_newval:
-                       if (sym->dir_dep.tri == no && sym->rev_dep.tri != no) {
-                               struct expr *e;
-                               e = expr_simplify_unmet_dep(sym->rev_dep.expr,
-                                   sym->dir_dep.expr);
-                               fprintf(stderr, "warning: (");
-                               expr_fprint(e, stderr);
-                               fprintf(stderr, ") selects %s which has unmet 
direct dependencies (",
-                                       sym->name);
-                               expr_fprint(sym->dir_dep.expr, stderr);
-                               fprintf(stderr, ")\n");
-                               expr_free(e);
-                       }
+                       if (sym->dir_dep.tri == no && sym->rev_dep.tri != no)
+                               sym_warn_unmet_dependency(sym);
                        newval.tri = EXPR_OR(newval.tri, sym->rev_dep.tri);
                }
                if (newval.tri == mod &&
-- 
2.7.4

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