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"
          depends on DEP2
          select C

  config B
          bool "B"
          select C

  config C
          bool
          depends on DEP1 && DEP2

[Result]

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

Here, I see some points to be improved.

First, '(A || B)' would make more sense than '(A && B)'.  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, 'A' never causes unmet dependency because 'DEP1' is fixed to
'y', and 'A' correctly depends on 'DEP2'.  It will be better to not
report 'A', but it is impossible to avoid this false positive in the
current expr_simplify_unmet_dep().

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>
---

 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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